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Frequently Asked Questions (FAQ) for PostgreSQL
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Last updated: Wed Dec 5 00:41:12 EST 2001
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Last updated: Fri Jan 4 00:44:42 EST 2002
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Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
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@ -58,42 +58,39 @@
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Operational Questions
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4.1) Why is the system confused about commas, decimal points, and date
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formats.
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4.2) What is the exact difference between binary cursors and normal
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cursors?
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4.3) How do I SELECT only the first few rows of a query?
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4.4) How do I get a list of tables or other things I can see in psql?
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4.5) How do you remove a column from a table?
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4.6) What is the maximum size for a row, table, database?
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4.7) How much database disk space is required to store data from a
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4.1) What is the difference between binary cursors and normal cursors?
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4.2) How do I SELECT only the first few rows of a query?
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4.3) How do I get a list of tables or other things I can see in psql?
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4.4) How do you remove a column from a table?
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4.5) What is the maximum size for a row, table, database?
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4.6) How much database disk space is required to store data from a
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typical text file?
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4.8) How do I find out what tables or indexes are defined in the
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4.7) How do I find out what tables or indexes are defined in the
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database?
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4.9) My queries are slow or don't make use of the indexes. Why?
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4.10) How do I see how the query optimizer is evaluating my query?
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4.11) What is an R-tree index?
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4.12) What is the Genetic Query Optimizer?
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4.13) How do I perform regular expression searches and
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4.8) My queries are slow or don't make use of the indexes. Why?
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4.9) How do I see how the query optimizer is evaluating my query?
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4.10) What is an R-tree index?
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4.11) What is the Genetic Query Optimizer?
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4.12) How do I perform regular expression searches and
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case-insensitive regular expression searches? How do I use an index
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for case-insensitive searches?
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4.14) In a query, how do I detect if a field is NULL?
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4.15) What is the difference between the various character types?
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4.16.1) How do I create a serial/auto-incrementing field?
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4.16.2) How do I get the value of a SERIAL insert?
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4.16.3) Don't currval() and nextval() lead to a race condition with
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4.13) In a query, how do I detect if a field is NULL?
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4.14) What is the difference between the various character types?
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4.15.1) How do I create a serial/auto-incrementing field?
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4.15.2) How do I get the value of a SERIAL insert?
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4.15.3) Don't currval() and nextval() lead to a race condition with
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other users?
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4.17) What is an OID? What is a TID?
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4.18) What is the meaning of some of the terms used in PostgreSQL?
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4.19) Why do I get the error "ERROR: Memory exhausted in
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4.16) What is an OID? What is a TID?
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4.17) What is the meaning of some of the terms used in PostgreSQL?
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4.18) Why do I get the error "ERROR: Memory exhausted in
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AllocSetAlloc()?"
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4.20) How do I tell what PostgreSQL version I am running?
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4.21) My large-object operations get invalid large obj descriptor.
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4.19) How do I tell what PostgreSQL version I am running?
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4.20) My large-object operations get invalid large obj descriptor.
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Why?
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4.22) How do I create a column that will default to the current time?
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4.23) Why are my subqueries using IN so slow?
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4.24) How do I perform an outer join?
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4.25) How do I perform queries using multiple databases?
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4.21) How do I create a column that will default to the current time?
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4.22) Why are my subqueries using IN so slow?
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4.23) How do I perform an outer join?
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4.24) How do I perform queries using multiple databases?
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Extending PostgreSQL
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@ -611,19 +608,11 @@
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Operational Questions
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4.1) Why is system confused about commas, decimal points, and date formats.
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Check your locale configuration. PostgreSQL uses the locale setting of
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the user that ran the postmaster process. There are postgres and psql
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SET commands to control the date format. Set those accordingly for
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your operating environment.
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4.2) What is the exact difference between binary cursors and normal
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cursors?
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4.1) What is the difference between binary cursors and normal cursors?
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See the DECLARE manual page for a description.
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4.3) How do I SELECT only the first few rows of a query?
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4.2) How do I SELECT only the first few rows of a query?
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See the FETCH manual page, or use SELECT ... LIMIT....
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@ -633,7 +622,7 @@
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only the first few records requested, or the entire query may have to
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be evaluated until the desired rows have been generated.
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4.4) How do I get a list of tables or other things I can see in psql?
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4.3) How do I get a list of tables or other things I can see in psql?
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You can read the source code for psql in file
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pgsql/src/bin/psql/describe.c. It contains SQL commands that generate
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@ -641,7 +630,7 @@
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the -E option so it will print out the queries it uses to execute the
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commands you give.
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4.5) How do you remove a column from a table?
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4.4) How do you remove a column from a table?
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We do not support ALTER TABLE DROP COLUMN, but do this:
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SELECT ... -- select all columns but the one you want to remove
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@ -650,7 +639,7 @@
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DROP TABLE old_table;
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ALTER TABLE new_table RENAME TO old_table;
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4.6) What is the maximum size for a row, table, database?
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4.5) What is the maximum size for a row, table, database?
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These are the limits:
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Maximum size for a database? unlimited (60GB databases exist)
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@ -672,7 +661,7 @@
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The maximum table size and maximum number of columns can be increased
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if the default block size is increased to 32k.
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4.7) How much database disk space is required to store data from a typical
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4.6) How much database disk space is required to store data from a typical
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text file?
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A PostgreSQL database may need six-and-a-half times the disk space
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@ -702,7 +691,7 @@
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Indexes do not require as much overhead, but do contain the data that
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is being indexed, so they can be large also.
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4.8) How do I find out what tables or indexes are defined in the database?
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4.7) How do I find out what tables or indexes are defined in the database?
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psql has a variety of backslash commands to show such information. Use
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\? to see them.
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@ -711,7 +700,7 @@
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many of the SELECTs needed to get information from the database system
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tables.
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4.9) My queries are slow or don't make use of the indexes. Why?
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4.8) My queries are slow or don't make use of the indexes. Why?
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PostgreSQL does not automatically maintain statistics. VACUUM must be
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run to update the statistics. After statistics are updated, the
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@ -736,11 +725,11 @@
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string. So, to use indices, LIKE searches should not begin with %, and
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~(regular expression searches) should start with ^.
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4.10) How do I see how the query optimizer is evaluating my query?
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4.9) How do I see how the query optimizer is evaluating my query?
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See the EXPLAIN manual page.
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4.11) What is an R-tree index?
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4.10) What is an R-tree index?
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An R-tree index is used for indexing spatial data. A hash index can't
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handle range searches. A B-tree index only handles range searches in a
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@ -763,13 +752,13 @@
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extending R-trees requires a bit of work and we don't currently have
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any documentation on how to do it.
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4.12) What is the Genetic Query Optimizer?
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4.11) What is the Genetic Query Optimizer?
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The GEQO module speeds query optimization when joining many tables by
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means of a Genetic Algorithm (GA). It allows the handling of large
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join queries through nonexhaustive search.
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4.13) How do I perform regular expression searches and case-insensitive
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4.12) How do I perform regular expression searches and case-insensitive
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regular expression searches? How do I use an index for case-insensitive
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searches?
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@ -788,11 +777,11 @@
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CREATE INDEX tabindex on tab (lower(col));
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4.14) In a query, how do I detect if a field is NULL?
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4.13) In a query, how do I detect if a field is NULL?
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You test the column with IS NULLIS NOT NULL.
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4.15) What is the difference between the various character types?
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4.14) What is the difference between the various character types?
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Type Internal Name Notes
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--------------------------------------------------
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@ -817,7 +806,7 @@ BYTEA bytea variable-length byte array (null-safe)
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maximum 1 gigabyte. BYTEA is for storing binary data, particularly
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values that include NULL bytes.
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4.16.1) How do I create a serial/auto-incrementing field?
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4.15.1) How do I create a serial/auto-incrementing field?
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PostgreSQL supports a SERIAL data type. It auto-creates a sequence and
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index on the column. For example, this:
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@ -841,11 +830,11 @@ BYTEA bytea variable-length byte array (null-safe)
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Numbering Rows.
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4.16.2) How do I get the value of a SERIAL insert?
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4.15.2) How do I get the value of a SERIAL insert?
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One approach is to to retrieve the next SERIAL value from the sequence
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object with the nextval() function before inserting and then insert it
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explicitly. Using the example table in 4.16.1, that might look like
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explicitly. Using the example table in 4.15.1, that might look like
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this in Perl:
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new_id = output of "SELECT nextval('person_id_seq')"
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INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal');
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@ -867,13 +856,13 @@ BYTEA bytea variable-length byte array (null-safe)
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oid value is made available via $sth->{pg_oid_status} after
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$sth->execute().
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4.16.3) Don't currval() and nextval() lead to a race condition with other
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4.15.3) Don't currval() and nextval() lead to a race condition with other
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users?
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No. Currval() returns the current value assigned by your backend, not
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by all users.
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4.17) What is an OID? What is a TID?
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4.16) What is an OID? What is a TID?
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OIDs are PostgreSQL's answer to unique row ids. Every row that is
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created in PostgreSQL gets a unique OID. All OIDs generated during
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@ -906,7 +895,7 @@ BYTEA bytea variable-length byte array (null-safe)
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values. Tids change after rows are modified or reloaded. They are used
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by index entries to point to physical rows.
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4.18) What is the meaning of some of the terms used in PostgreSQL?
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4.17) What is the meaning of some of the terms used in PostgreSQL?
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Some of the source code and older documentation use terms that have
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more common usage. Here are some:
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@ -923,7 +912,7 @@ BYTEA bytea variable-length byte array (null-safe)
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A list of general database terms can be found at:
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http://www.comptechnews.com/~reaster/dbdesign.html
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4.19) Why do I get the error "ERROR: Memory exhausted in AllocSetAlloc()?"
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4.18) Why do I get the error "ERROR: Memory exhausted in AllocSetAlloc()?"
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If you are running a version older than 7.1, an upgrade may fix the
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problem. Also it is possible you have run out of virtual memory on
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@ -939,11 +928,11 @@ BYTEA bytea variable-length byte array (null-safe)
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problem with the SQL client because the backend is returning too much
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data, try it before starting the client.
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4.20) How do I tell what PostgreSQL version I am running?
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4.19) How do I tell what PostgreSQL version I am running?
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From psql, type select version();
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4.21) My large-object operations get invalid large obj descriptor. Why?
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4.20) My large-object operations get invalid large obj descriptor. Why?
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You need to put BEGIN WORK and COMMIT around any use of a large object
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handle, that is, surrounding lo_open ... lo_close.
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@ -957,12 +946,12 @@ BYTEA bytea variable-length byte array (null-safe)
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If you are using a client interface like ODBC you may need to set
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auto-commit off.
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4.22) How do I create a column that will default to the current time?
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4.21) How do I create a column that will default to the current time?
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Use CURRENT_TIMESTAMP:
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CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
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4.23) Why are my subqueries using IN so slow?
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4.22) Why are my subqueries using IN so slow?
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Currently, we join subqueries to outer queries by sequentially
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scanning the result of the subquery for each row of the outer query. A
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@ -978,7 +967,7 @@ SELECT *
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We hope to fix this limitation in a future release.
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4.24) How do I perform an outer join?
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4.23) How do I perform an outer join?
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PostgreSQL 7.1 and later supports outer joins using the SQL standard
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syntax. Here are two examples:
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@ -1008,7 +997,7 @@ SELECT *
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WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2)
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ORDER BY col1
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4.25) How do I perform queries using multiple databases?
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4.24) How do I perform queries using multiple databases?
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There is no way to query any database except the current one. Because
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PostgreSQL loads database-specific system catalogs, it is uncertain
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@ -11,7 +11,7 @@
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alink="#0000FF">
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<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
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<P>Last updated: Wed Dec 5 00:41:12 EST 2001</P>
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<P>Last updated: Fri Jan 4 00:44:42 EST 2002</P>
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<P>Current maintainer: Bruce Momjian (<A href=
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"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
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@ -89,57 +89,55 @@
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<CENTER>
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<H2>Operational Questions</H2>
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</CENTER>
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<A href="#4.1">4.1</A>) Why is the system confused about commas,
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decimal points, and date formats.<BR>
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<A href="#4.2">4.2</A>) What is the exact difference between
|
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<A href="#4.1">4.1</A>) What is the difference between
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binary cursors and normal cursors?<BR>
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<A href="#4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the
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<A href="#4.2">4.2</A>) How do I <SMALL>SELECT</SMALL> only the
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first few rows of a query?<BR>
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<A href="#4.4">4.4</A>) How do I get a list of tables or other
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<A href="#4.3">4.3</A>) How do I get a list of tables or other
|
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things I can see in <I>psql?</I><BR>
|
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<A href="#4.5">4.5</A>) How do you remove a column from a
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<A href="#4.4">4.4</A>) How do you remove a column from a
|
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table?<BR>
|
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<A href="#4.6">4.6</A>) What is the maximum size for a row, table,
|
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<A href="#4.5">4.5</A>) What is the maximum size for a row, table,
|
||||
database?<BR>
|
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<A href="#4.7">4.7</A>) How much database disk space is required
|
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<A href="#4.6">4.6</A>) How much database disk space is required
|
||||
to store data from a typical text file?<BR>
|
||||
<A href="#4.8">4.8</A>) How do I find out what tables or indexes
|
||||
<A href="#4.7">4.7</A>) How do I find out what tables or indexes
|
||||
are defined in the database?<BR>
|
||||
<A href="#4.9">4.9</A>) My queries are slow or don't make use of
|
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<A href="#4.8">4.8</A>) My queries are slow or don't make use of
|
||||
the indexes. Why?<BR>
|
||||
<A href="#4.10">4.10</A>) How do I see how the query optimizer is
|
||||
<A href="#4.9">4.9</A>) How do I see how the query optimizer is
|
||||
evaluating my query?<BR>
|
||||
<A href="#4.11">4.11</A>) What is an R-tree index?<BR>
|
||||
<A href="#4.12">4.12</A>) What is the Genetic Query Optimizer?<BR>
|
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<A href="#4.13">4.13</A>) How do I perform regular expression
|
||||
<A href="#4.10">4.10</A>) What is an R-tree index?<BR>
|
||||
<A href="#4.11">4.11</A>) What is the Genetic Query Optimizer?<BR>
|
||||
<A href="#4.12">4.12</A>) How do I perform regular expression
|
||||
searches and case-insensitive regular expression searches? How do I
|
||||
use an index for case-insensitive searches?<BR>
|
||||
<A href="#4.14">4.14</A>) In a query, how do I detect if a field
|
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<A href="#4.13">4.13</A>) In a query, how do I detect if a field
|
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is <SMALL>NULL</SMALL>?<BR>
|
||||
<A href="#4.15">4.15</A>) What is the difference between the
|
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<A href="#4.14">4.14</A>) What is the difference between the
|
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various character types?<BR>
|
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<A href="#4.16.1">4.16.1</A>) How do I create a
|
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<A href="#4.15.1">4.15.1</A>) How do I create a
|
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serial/auto-incrementing field?<BR>
|
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<A href="#4.16.2">4.16.2</A>) How do I get the value of a
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<A href="#4.15.2">4.15.2</A>) How do I get the value of a
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<SMALL>SERIAL</SMALL> insert?<BR>
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<A href="#4.16.3">4.16.3</A>) Don't <I>currval()</I> and
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<A href="#4.15.3">4.15.3</A>) Don't <I>currval()</I> and
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<I>nextval()</I> lead to a race condition with other users?<BR>
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<A href="#4.17">4.17</A>) What is an <SMALL>OID</SMALL>? What is a
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<A href="#4.16">4.16</A>) What is an <SMALL>OID</SMALL>? What is a
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<SMALL>TID</SMALL>?<BR>
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<A href="#4.18">4.18</A>) What is the meaning of some of the terms
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<A href="#4.17">4.17</A>) What is the meaning of some of the terms
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used in PostgreSQL?<BR>
|
||||
<A href="#4.19">4.19</A>) Why do I get the error <I>"ERROR:
|
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<A href="#4.18">4.18</A>) Why do I get the error <I>"ERROR:
|
||||
Memory exhausted in AllocSetAlloc()?"</I><BR>
|
||||
<A href="#4.20">4.20</A>) How do I tell what PostgreSQL version I
|
||||
<A href="#4.19">4.19</A>) How do I tell what PostgreSQL version I
|
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am running? <BR>
|
||||
<A href="#4.21">4.21</A>) My large-object operations get
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<A href="#4.20">4.20</A>) My large-object operations get
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<I>invalid large obj descriptor.</I> Why?<BR>
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<A href="#4.22">4.22</A>) How do I create a column that will
|
||||
<A href="#4.21">4.21</A>) How do I create a column that will
|
||||
default to the current time?<BR>
|
||||
<A href="#4.23">4.23</A>) Why are my subqueries using
|
||||
<A href="#4.22">4.22</A>) Why are my subqueries using
|
||||
<CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
|
||||
<A href="#4.24">4.24</A>) How do I perform an outer join?<BR>
|
||||
<A href="#4.25">4.25</A>) How do I perform queries using multiple databases?<BR>
|
||||
<A href="#4.23">4.23</A>) How do I perform an outer join?<BR>
|
||||
<A href="#4.24">4.24</A>) How do I perform queries using multiple databases?<BR>
|
||||
|
||||
|
||||
<CENTER>
|
||||
@ -788,22 +786,13 @@
|
||||
<H2>Operational Questions</H2>
|
||||
</CENTER>
|
||||
|
||||
<H4><A name="4.1">4.1</A>) Why is system confused about commas,
|
||||
decimal points, and date formats.</H4>
|
||||
|
||||
<P>Check your locale configuration. PostgreSQL uses the locale
|
||||
setting of the user that ran the <I>postmaster</I> process. There
|
||||
are postgres and psql <SMALL>SET</SMALL> commands to control the
|
||||
date format. Set those accordingly for your operating
|
||||
environment.</P>
|
||||
|
||||
<H4><A name="4.2">4.2</A>) What is the exact difference between
|
||||
<H4><A name="4.1">4.1</A>) What is the difference between
|
||||
binary cursors and normal cursors?</H4>
|
||||
|
||||
<P>See the <SMALL>DECLARE</SMALL> manual page for a
|
||||
description.</P>
|
||||
|
||||
<H4><A name="4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the
|
||||
<H4><A name="4.2">4.2</A>) How do I <SMALL>SELECT</SMALL> only the
|
||||
first few rows of a query?</H4>
|
||||
|
||||
<P>See the <SMALL>FETCH</SMALL> manual page, or use
|
||||
@ -816,7 +805,7 @@
|
||||
records requested, or the entire query may have to be evaluated
|
||||
until the desired rows have been generated.</P>
|
||||
|
||||
<H4><A name="4.4">4.4</A>) How do I get a list of tables or other
|
||||
<H4><A name="4.3">4.3</A>) How do I get a list of tables or other
|
||||
things I can see in <I>psql?</I><BR>
|
||||
</H4>
|
||||
|
||||
@ -827,7 +816,7 @@
|
||||
<I>-E</I> option so it will print out the queries it uses to
|
||||
execute the commands you give.</P>
|
||||
|
||||
<H4><A name="4.5">4.5</A>) How do you remove a column from a
|
||||
<H4><A name="4.4">4.4</A>) How do you remove a column from a
|
||||
table?</H4>
|
||||
|
||||
<P>We do not support <SMALL>ALTER TABLE DROP COLUMN,</SMALL> but do
|
||||
@ -840,7 +829,7 @@
|
||||
ALTER TABLE new_table RENAME TO old_table;
|
||||
</PRE>
|
||||
|
||||
<H4><A name="4.6">4.6</A>) What is the maximum size for a row,
|
||||
<H4><A name="4.5">4.5</A>) What is the maximum size for a row,
|
||||
table, database?</H4>
|
||||
|
||||
<P>These are the limits:</P>
|
||||
@ -864,7 +853,7 @@
|
||||
<P>The maximum table size and maximum number of columns can be
|
||||
increased if the default block size is increased to 32k.</P>
|
||||
|
||||
<H4><A name="4.7">4.7</A>) How much database disk space is required
|
||||
<H4><A name="4.6">4.6</A>) How much database disk space is required
|
||||
to store data from a typical text file?<BR>
|
||||
</H4>
|
||||
|
||||
@ -897,7 +886,7 @@
|
||||
<P>Indexes do not require as much overhead, but do contain the data
|
||||
that is being indexed, so they can be large also.</P>
|
||||
|
||||
<H4><A name="4.8">4.8</A>) How do I find out what tables or indexes
|
||||
<H4><A name="4.7">4.7</A>) How do I find out what tables or indexes
|
||||
are defined in the database?</H4>
|
||||
|
||||
<P><I>psql</I> has a variety of backslash commands to show such
|
||||
@ -907,7 +896,7 @@
|
||||
illustrates many of the <SMALL>SELECT</SMALL>s needed to get
|
||||
information from the database system tables.</P>
|
||||
|
||||
<H4><A name="4.9">4.9</A>) My queries are slow or don't make use of
|
||||
<H4><A name="4.8">4.8</A>) My queries are slow or don't make use of
|
||||
the indexes. Why?</H4>
|
||||
|
||||
<P>PostgreSQL does not automatically maintain statistics.
|
||||
@ -937,12 +926,12 @@
|
||||
<I>~</I>(regular expression searches) should start with
|
||||
<I>^.</I></P>
|
||||
|
||||
<H4><A name="4.10">4.10</A>) How do I see how the query optimizer
|
||||
<H4><A name="4.9">4.9</A>) How do I see how the query optimizer
|
||||
is evaluating my query?</H4>
|
||||
|
||||
<P>See the <SMALL>EXPLAIN</SMALL> manual page.</P>
|
||||
|
||||
<H4><A name="4.11">4.11</A>) What is an R-tree index?</H4>
|
||||
<H4><A name="4.10">4.10</A>) What is an R-tree index?</H4>
|
||||
|
||||
<P>An R-tree index is used for indexing spatial data. A hash index
|
||||
can't handle range searches. A B-tree index only handles range
|
||||
@ -967,7 +956,7 @@
|
||||
practice, extending R-trees requires a bit of work and we don't
|
||||
currently have any documentation on how to do it.</P>
|
||||
|
||||
<H4><A name="4.12">4.12</A>) What is the Genetic Query
|
||||
<H4><A name="4.11">4.11</A>) What is the Genetic Query
|
||||
Optimizer?</H4>
|
||||
|
||||
<P>The <SMALL>GEQO</SMALL> module speeds query optimization when
|
||||
@ -975,7 +964,7 @@
|
||||
the handling of large join queries through nonexhaustive
|
||||
search.</P>
|
||||
|
||||
<H4><A name="4.13">4.13</A>) How do I perform regular expression
|
||||
<H4><A name="4.12">4.12</A>) How do I perform regular expression
|
||||
searches and case-insensitive regular expression searches? How do I
|
||||
use an index for case-insensitive searches?</H4>
|
||||
|
||||
@ -999,12 +988,12 @@
|
||||
CREATE INDEX tabindex on tab (lower(col));
|
||||
</PRE>
|
||||
|
||||
<H4><A name="4.14">4.14</A>) In a query, how do I detect if a field
|
||||
<H4><A name="4.13">4.13</A>) In a query, how do I detect if a field
|
||||
is <SMALL>NULL</SMALL>?</H4>
|
||||
|
||||
<P>You test the column with <SMALL>IS NULL</SMALL>IS NOT NULL.</P>
|
||||
|
||||
<H4><A name="4.15">4.15</A>) What is the difference between the
|
||||
<H4><A name="4.14">4.14</A>) What is the difference between the
|
||||
various character types?</H4>
|
||||
<PRE>
|
||||
Type Internal Name Notes
|
||||
@ -1034,7 +1023,7 @@ BYTEA bytea variable-length byte array (null-safe)
|
||||
binary data, particularly values that include <SMALL>NULL</SMALL>
|
||||
bytes.</P>
|
||||
|
||||
<H4><A name="4.16.1">4.16.1</A>) How do I create a
|
||||
<H4><A name="4.15.1">4.15.1</A>) How do I create a
|
||||
serial/auto-incrementing field?</H4>
|
||||
|
||||
<P>PostgreSQL supports a <SMALL>SERIAL</SMALL> data type. It
|
||||
@ -1064,13 +1053,13 @@ BYTEA bytea variable-length byte array (null-safe)
|
||||
<P><A href="http://www.PostgreSQL.org/docs/aw_pgsql_book">Numbering
|
||||
Rows.</A></P>
|
||||
|
||||
<H4><A name="4.16.2">4.16.2</A>) How do I get the value of a
|
||||
<H4><A name="4.15.2">4.15.2</A>) How do I get the value of a
|
||||
<SMALL>SERIAL</SMALL> insert?</H4>
|
||||
|
||||
<P>One approach is to to retrieve the next <SMALL>SERIAL</SMALL>
|
||||
value from the sequence object with the <I>nextval()</I> function
|
||||
<I>before</I> inserting and then insert it explicitly. Using the
|
||||
example table in <A href="#4.16.1">4.16.1</A>, that might look like
|
||||
example table in <A href="#4.15.1">4.15.1</A>, that might look like
|
||||
this in Perl:</P>
|
||||
<PRE>
|
||||
new_id = output of "SELECT nextval('person_id_seq')"
|
||||
@ -1091,20 +1080,20 @@ BYTEA bytea variable-length byte array (null-safe)
|
||||
INSERT INTO person (name) VALUES ('Blaise Pascal');
|
||||
new_id = output of "SELECT currval('person_id_seq')";
|
||||
</PRE>
|
||||
Finally, you could use the <A href="#4.17"><SMALL>OID</SMALL></A>
|
||||
Finally, you could use the <A href="#4.16"><SMALL>OID</SMALL></A>
|
||||
returned from the <SMALL>INSERT</SMALL> statement to look up the
|
||||
default value, though this is probably the least portable approach.
|
||||
In Perl, using DBI with Edmund Mergl's DBD::Pg module, the oid
|
||||
value is made available via <I>$sth->{pg_oid_status} after
|
||||
$sth->execute().</I>
|
||||
|
||||
<H4><A name="4.16.3">4.16.3</A>) Don't <I>currval()</I> and
|
||||
<H4><A name="4.15.3">4.15.3</A>) Don't <I>currval()</I> and
|
||||
<I>nextval()</I> lead to a race condition with other users?</H4>
|
||||
|
||||
<P>No. Currval() returns the current value assigned by your
|
||||
backend, not by all users.</P>
|
||||
|
||||
<H4><A name="4.17">4.17</A>) What is an <SMALL>OID</SMALL>? What is
|
||||
<H4><A name="4.16">4.16</A>) What is an <SMALL>OID</SMALL>? What is
|
||||
a <SMALL>TID</SMALL>?</H4>
|
||||
|
||||
<P><SMALL>OID</SMALL>s are PostgreSQL's answer to unique row ids.
|
||||
@ -1149,7 +1138,7 @@ BYTEA bytea variable-length byte array (null-safe)
|
||||
or reloaded. They are used by index entries to point to physical
|
||||
rows.</P>
|
||||
|
||||
<H4><A name="4.18">4.18</A>) What is the meaning of some of the
|
||||
<H4><A name="4.17">4.17</A>) What is the meaning of some of the
|
||||
terms used in PostgreSQL?</H4>
|
||||
|
||||
<P>Some of the source code and older documentation use terms that
|
||||
@ -1178,7 +1167,7 @@ BYTEA bytea variable-length byte array (null-safe)
|
||||
<P>A list of general database terms can be found at: <A href=
|
||||
"http://www.comptechnews.com/~reaster/dbdesign.html">http://www.comptechnews.com/~reaster/dbdesign.html</A></P>
|
||||
|
||||
<H4><A name="4.19">4.19</A>) Why do I get the error <I>"ERROR:
|
||||
<H4><A name="4.18">4.18</A>) Why do I get the error <I>"ERROR:
|
||||
Memory exhausted in AllocSetAlloc()?"</I><BR>
|
||||
</H4>
|
||||
|
||||
@ -1198,13 +1187,13 @@ BYTEA bytea variable-length byte array (null-safe)
|
||||
backend is returning too much data, try it before starting the
|
||||
client.
|
||||
|
||||
<H4><A name="4.20">4.20</A>) How do I tell what PostgreSQL version
|
||||
<H4><A name="4.19">4.19</A>) How do I tell what PostgreSQL version
|
||||
I am running?<BR>
|
||||
</H4>
|
||||
|
||||
<P>From <I>psql,</I> type <CODE>select version();</CODE></P>
|
||||
|
||||
<H4><A name="4.21">4.21</A>) My large-object operations get
|
||||
<H4><A name="4.20">4.20</A>) My large-object operations get
|
||||
<I>invalid large obj descriptor.</I> Why?<BR>
|
||||
</H4>
|
||||
|
||||
@ -1221,7 +1210,7 @@ BYTEA bytea variable-length byte array (null-safe)
|
||||
<P>If you are using a client interface like <SMALL>ODBC</SMALL> you
|
||||
may need to set <CODE>auto-commit off.</CODE></P>
|
||||
|
||||
<H4><A name="4.22">4.22</A>) How do I create a column that will
|
||||
<H4><A name="4.21">4.21</A>) How do I create a column that will
|
||||
default to the current time?<BR>
|
||||
</H4>
|
||||
|
||||
@ -1231,7 +1220,7 @@ BYTEA bytea variable-length byte array (null-safe)
|
||||
</CODE>
|
||||
</PRE>
|
||||
|
||||
<H4><A name="4.23">4.23</A>) Why are my subqueries using
|
||||
<H4><A name="4.22">4.22</A>) Why are my subqueries using
|
||||
<CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
|
||||
</H4>
|
||||
|
||||
@ -1254,7 +1243,7 @@ BYTEA bytea variable-length byte array (null-safe)
|
||||
</PRE>
|
||||
We hope to fix this limitation in a future release.
|
||||
|
||||
<H4><A name="4.24">4.24</A>) How do I perform an outer join?<BR>
|
||||
<H4><A name="4.23">4.23</A>) How do I perform an outer join?<BR>
|
||||
</H4>
|
||||
|
||||
<P>PostgreSQL 7.1 and later supports outer joins using the SQL
|
||||
@ -1295,7 +1284,7 @@ BYTEA bytea variable-length byte array (null-safe)
|
||||
ORDER BY col1
|
||||
</PRE>
|
||||
|
||||
<H4><A href="#4.25">4.25</A>) How do I perform queries
|
||||
<H4><A href="#4.24">4.24</A>) How do I perform queries
|
||||
using multiple databases?</H4>
|
||||
|
||||
<P>There is no way to query any database except the current one.
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user