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Remove GEQO and Rtree FAQ items.
This commit is contained in:
Bruce Momjian
parent
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commit
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115
doc/FAQ
115
doc/FAQ
@ -1,7 +1,7 @@
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Frequently Asked Questions (FAQ) for PostgreSQL
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Last updated: Sat Jan 29 23:06:02 EST 2005
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Last updated: Sat Jan 29 23:15:42 EST 2005
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Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
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@ -58,33 +58,31 @@
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typical text file?
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4.6) Why are my queries slow? Why don't they use my indexes?
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4.7) How do I see how the query optimizer is evaluating my query?
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4.8) What is an R-tree index?
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4.9) What is the Genetic Query Optimizer?
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4.10) 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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4.11) In a query, how do I detect if a field is NULL?
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4.12) What is the difference between the various character types?
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4.13.0) How do I create a serial/auto-incrementing field?
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4.13.1) How do I get the value of a SERIAL insert?
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4.13.2) Doesn't currval() lead to a race condition with other users?
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4.13.3) Why aren't my sequence numbers reused on transaction abort?
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4.8) How do I perform regular expression searches and case-insensitive
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regular expression searches? How do I use an index for
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case-insensitive searches?
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4.9) In a query, how do I detect if a field is NULL?
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4.10) What is the difference between the various character types?
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4.11.0) How do I create a serial/auto-incrementing field?
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4.11.1) How do I get the value of a SERIAL insert?
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4.11.2) Doesn't currval() lead to a race condition with other users?
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4.11.3) Why aren't my sequence numbers reused on transaction abort?
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Why are there gaps in the numbering of my sequence/SERIAL column?
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4.14) What is an OID? What is a TID?
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4.15) What is the meaning of some of the terms used in PostgreSQL?
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4.16) Why do I get the error "ERROR: Memory exhausted in
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4.12) What is an OID? What is a TID?
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4.13) What is the meaning of some of the terms used in PostgreSQL?
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4.14) Why do I get the error "ERROR: Memory exhausted in
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AllocSetAlloc()"?
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4.17) How do I tell what PostgreSQL version I am running?
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4.18) Why does my large-object operations get "invalid large obj
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4.15) How do I tell what PostgreSQL version I am running?
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4.16) Why does my large-object operations get "invalid large obj
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descriptor"?
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4.19) How do I create a column that will default to the current time?
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4.20) Why are my subqueries using IN so slow?
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4.21) How do I perform an outer join?
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4.22) How do I perform queries using multiple databases?
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4.23) How do I return multiple rows or columns from a function?
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4.24) Why can't I reliably create/drop temporary tables in PL/PgSQL
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4.17) How do I create a column that will default to the current time?
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4.18) Why are my subqueries using IN so slow?
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4.19) How do I perform an outer join?
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4.20) How do I perform queries using multiple databases?
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4.21) How do I return multiple rows or columns from a function?
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4.22) Why can't I reliably create/drop temporary tables in PL/PgSQL
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functions?
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4.25) What encryption options are available?
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4.23) What encryption options are available?
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Extending PostgreSQL
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@ -742,36 +740,7 @@ LIKE
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See the EXPLAIN manual page.
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4.8) 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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single dimension. R-trees can handle multi-dimensional data. For
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example, if an R-tree index can be built on an attribute of type
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point, the system can more efficiently answer queries such as "select
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all points within a bounding rectangle."
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The canonical paper that describes the original R-tree design is:
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Guttman, A. "R-trees: A Dynamic Index Structure for Spatial
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Searching." Proceedings of the 1984 ACM SIGMOD Int'l Conf on Mgmt of
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Data, 45-57.
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You can also find this paper in Stonebraker's "Readings in Database
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Systems".
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Built-in R-trees can handle polygons and boxes. In theory, R-trees can
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be extended to handle higher number of dimensions. In practice,
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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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4.9) 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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4.10) How do I perform regular expression searches and case-insensitive
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4.8) 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 +757,11 @@ LIKE
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functional index, it will be used:
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CREATE INDEX tabindex ON tab (lower(col));
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4.11) In a query, how do I detect if a field is NULL?
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4.9) In a query, how do I detect if a field is NULL?
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You test the column with IS NULL and IS NOT NULL.
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4.12) What is the difference between the various character types?
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4.10) 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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@ -820,7 +789,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
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particularly values that include NULL bytes. All the types described
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here have similar performance characteristics.
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4.13.1) How do I create a serial/auto-incrementing field?
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4.11.1) How do I create a serial/auto-incrementing field?
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PostgreSQL supports a SERIAL data type. It auto-creates a sequence.
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For example, this:
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@ -841,11 +810,11 @@ BYTEA bytea variable-length byte array (null-byte safe)
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However, if you need to dump and reload the database, you need to use
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pg_dump's -o option or COPY WITH OIDS option to preserve the OIDs.
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4.13.2) How do I get the value of a SERIAL insert?
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4.11.2) How do I get the value of a SERIAL insert?
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One approach is 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 4.13.1, an example in a
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explicitly. Using the example table in 4.11.1, an example in a
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pseudo-language would look like this:
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new_id = execute("SELECT nextval('person_id_seq')");
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execute("INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal')");
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@ -867,19 +836,19 @@ BYTEA bytea variable-length byte array (null-byte safe)
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billion. In Perl, using DBI with the DBD::Pg module, the oid value is
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made available via $sth->{pg_oid_status} after $sth->execute().
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4.13.3) Doesn't currval() lead to a race condition with other users?
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4.11.3) Doesn't currval() lead to a race condition with other 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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4.13.4) Why aren't my sequence numbers reused on transaction abort? Why are
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4.11.4) Why aren't my sequence numbers reused on transaction abort? Why are
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there gaps in the numbering of my sequence/SERIAL column?
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To improve concurrency, sequence values are given out to running
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transactions as needed and are not locked until the transaction
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completes. This causes gaps in numbering from aborted transactions.
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4.14) What is an OID? What is a TID?
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4.12) What is an OID? What is a TID?
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Every row that is created in PostgreSQL gets a unique OID unless
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created WITHOUT OIDS. OIDs are autotomatically assigned unique 4-byte
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@ -896,7 +865,7 @@ BYTEA bytea variable-length byte array (null-byte 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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4.15) What is the meaning of some of the terms used in PostgreSQL?
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4.13) 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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@ -914,7 +883,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
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http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary
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/glossary.html
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4.16) Why do I get the error "ERROR: Memory exhausted in AllocSetAlloc()"?
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4.14) Why do I get the error "ERROR: Memory exhausted in AllocSetAlloc()"?
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You probably have run out of virtual memory on your system, or your
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kernel has a low limit for certain resources. Try this before starting
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@ -929,11 +898,11 @@ BYTEA bytea variable-length byte array (null-byte 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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4.17) How do I tell what PostgreSQL version I am running?
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4.15) How do I tell what PostgreSQL version I am running?
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From psql, type SELECT version();
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4.18) Why does my large-object operations get "invalid large obj
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4.16) Why does my large-object operations get "invalid large obj
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descriptor"?
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You need to put BEGIN WORK and COMMIT around any use of a large object
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@ -948,12 +917,12 @@ BYTEA bytea variable-length byte array (null-byte 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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4.19) How do I create a column that will default to the current time?
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4.17) 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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4.20) Why are my subqueries using IN so slow?
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4.18) Why are my subqueries using IN so slow?
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In versions prior to 7.4, subqueries were joined to outer queries by
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sequentially scanning the result of the subquery for each row of the
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@ -974,7 +943,7 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
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In version 7.4 and later, IN actually uses the same sophisticated join
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techniques as normal queries, and is prefered to using EXISTS.
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4.21) How do I perform an outer join?
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4.19) How do I perform an outer join?
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PostgreSQL supports outer joins using the SQL standard syntax. Here
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are two examples:
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@ -1004,7 +973,7 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
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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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4.22) How do I perform queries using multiple databases?
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4.20) How do I perform queries using multiple databases?
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There is no way to query a database other than the current one.
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Because PostgreSQL loads database-specific system catalogs, it is
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@ -1014,12 +983,12 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
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course, a client can make simultaneous connections to different
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databases and merge the results on the client side.
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4.23) How do I return multiple rows or columns from a function?
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4.21) How do I return multiple rows or columns from a function?
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In 7.3, you can easily return multiple rows or columns from a
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function, http://techdocs.postgresql.org/guides/SetReturningFunctions.
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4.24) Why can't I reliably create/drop temporary tables in PL/PgSQL
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4.22) Why can't I reliably create/drop temporary tables in PL/PgSQL
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functions?
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PL/PgSQL caches function contents, and an unfortunate side effect is
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@ -1030,7 +999,7 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
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table access in PL/PgSQL. This will cause the query to be reparsed
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every time.
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4.25) What encryption options are available?
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4.23) What encryption options are available?
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* contrib/pgcrypto contains many encryption functions for use in SQL
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queries.
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@ -10,7 +10,7 @@
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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: Sat Jan 29 23:06:02 EST 2005</P>
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<P>Last updated: Sat Jan 29 23:15:42 EST 2005</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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@ -86,46 +86,44 @@
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use my indexes?<BR>
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<A href="#4.7">4.7</A>) How do I see how the query optimizer is
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evaluating my query?<BR>
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<A href="#4.8">4.8</A>) What is an R-tree index?<BR>
|
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<A href="#4.9">4.9</A>) What is the Genetic Query Optimizer?<BR>
|
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<A href="#4.10">4.10</A>) How do I perform regular expression
|
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<A href="#4.8">4.8</A>) How do I perform regular expression
|
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searches and case-insensitive regular expression searches? How do I
|
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use an index for case-insensitive searches?<BR>
|
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<A href="#4.11">4.11</A>) In a query, how do I detect if a field
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<A href="#4.9">4.9</A>) In a query, how do I detect if a field
|
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is <SMALL>NULL</SMALL>?<BR>
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<A href="#4.12">4.12</A>) What is the difference between the
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<A href="#4.10">4.10</A>) What is the difference between the
|
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various character types?<BR>
|
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<A href="#4.13.0">4.13.0</A>) How do I create a
|
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<A href="#4.11.0">4.11.0</A>) How do I create a
|
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serial/auto-incrementing field?<BR>
|
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<A href="#4.13.1">4.13.1</A>) How do I get the value of a
|
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<A href="#4.11.1">4.11.1</A>) How do I get the value of a
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<SMALL>SERIAL</SMALL> insert?<BR>
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<A href="#4.13.2">4.13.2</A>) Doesn't <I>currval()</I>
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<A href="#4.11.2">4.11.2</A>) Doesn't <I>currval()</I>
|
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lead to a race condition with other users?<BR>
|
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<A href="#4.13.3">4.13.3</A>) Why aren't my sequence numbers
|
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<A href="#4.11.3">4.11.3</A>) Why aren't my sequence numbers
|
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reused on transaction abort? Why are there gaps in the numbering of
|
||||
my sequence/SERIAL column?<BR>
|
||||
<A href="#4.14">4.14</A>) What is an <SMALL>OID</SMALL>? What is a
|
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<A href="#4.12">4.12</A>) What is an <SMALL>OID</SMALL>? What is a
|
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<SMALL>TID</SMALL>?<BR>
|
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<A href="#4.15">4.15</A>) What is the meaning of some of the terms
|
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<A href="#4.13">4.13</A>) What is the meaning of some of the terms
|
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used in PostgreSQL?<BR>
|
||||
<A href="#4.16">4.16</A>) Why do I get the error <I>"ERROR: Memory
|
||||
<A href="#4.14">4.14</A>) Why do I get the error <I>"ERROR: Memory
|
||||
exhausted in AllocSetAlloc()"</I>?<BR>
|
||||
<A href="#4.17">4.17</A>) How do I tell what PostgreSQL version I
|
||||
<A href="#4.15">4.15</A>) How do I tell what PostgreSQL version I
|
||||
am running?<BR>
|
||||
<A href="#4.18">4.18</A>) Why does my large-object operations get
|
||||
<A href="#4.16">4.16</A>) Why does my large-object operations get
|
||||
<I>"invalid large obj descriptor"</I>?<BR>
|
||||
<A href="#4.19">4.19</A>) How do I create a column that will
|
||||
<A href="#4.17">4.17</A>) How do I create a column that will
|
||||
default to the current time?<BR>
|
||||
<A href="#4.20">4.20</A>) Why are my subqueries using
|
||||
<A href="#4.18">4.18</A>) Why are my subqueries using
|
||||
<CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
|
||||
<A href="#4.21">4.21</A>) How do I perform an outer join?<BR>
|
||||
<A href="#4.22">4.22</A>) How do I perform queries using multiple
|
||||
<A href="#4.19">4.19</A>) How do I perform an outer join?<BR>
|
||||
<A href="#4.20">4.20</A>) How do I perform queries using multiple
|
||||
databases?<BR>
|
||||
<A href="#4.23">4.23</A>) How do I return multiple rows or columns
|
||||
<A href="#4.21">4.21</A>) How do I return multiple rows or columns
|
||||
from a function?<BR>
|
||||
<A href="#4.24">4.24</A>) Why can't I reliably create/drop
|
||||
<A href="#4.22">4.22</A>) Why can't I reliably create/drop
|
||||
temporary tables in PL/PgSQL functions?<BR>
|
||||
<A href="#4.25">4.25</A>) What encryption options are available?<BR>
|
||||
<A href="#4.23">4.23</A>) What encryption options are available?<BR>
|
||||
|
||||
|
||||
<H2 align="center">Extending PostgreSQL</H2>
|
||||
@ -915,40 +913,7 @@
|
||||
|
||||
<P>See the <SMALL>EXPLAIN</SMALL> manual page.</P>
|
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|
||||
<H4><A name="4.8">4.8</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
|
||||
searches in a single dimension. R-trees can handle
|
||||
multi-dimensional data. For example, if an R-tree index can be
|
||||
built on an attribute of type <I>point</I>, the system can more
|
||||
efficiently answer queries such as "select all points within a
|
||||
bounding rectangle."</P>
|
||||
|
||||
<P>The canonical paper that describes the original R-tree design
|
||||
is:</P>
|
||||
|
||||
<P>Guttman, A. "R-trees: A Dynamic Index Structure for Spatial
|
||||
Searching." Proceedings of the 1984 ACM SIGMOD Int'l Conf on Mgmt
|
||||
of Data, 45-57.</P>
|
||||
|
||||
<P>You can also find this paper in Stonebraker's "Readings in
|
||||
Database Systems".</P>
|
||||
|
||||
<P>Built-in R-trees can handle polygons and boxes. In theory,
|
||||
R-trees can be extended to handle higher number of dimensions. In
|
||||
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="4.9">4.9</A>) What is the Genetic Query
|
||||
Optimizer?</H4>
|
||||
|
||||
<P>The <SMALL>GEQO</SMALL> module speeds query optimization when
|
||||
joining many tables by means of a Genetic Algorithm (GA). It allows
|
||||
the handling of large join queries through nonexhaustive
|
||||
search.</P>
|
||||
|
||||
<H4><A name="4.10">4.10</A>) How do I perform regular expression
|
||||
<H4><A name="4.8">4.8</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>
|
||||
|
||||
@ -971,13 +936,13 @@
|
||||
CREATE INDEX tabindex ON tab (lower(col));
|
||||
</PRE>
|
||||
|
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<H4><A name="4.11">4.11</A>) In a query, how do I detect if a field
|
||||
<H4><A name="4.9">4.9</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> and <SMALL>IS
|
||||
NOT NULL</SMALL>.</P>
|
||||
|
||||
<H4><A name="4.12">4.12</A>) What is the difference between the
|
||||
<H4><A name="4.10">4.10</A>) What is the difference between the
|
||||
various character types?</H4>
|
||||
<PRE>
|
||||
Type Internal Name Notes
|
||||
@ -1009,7 +974,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
particularly values that include <SMALL>NULL</SMALL> bytes. All the
|
||||
types described here have similar performance characteristics.</P>
|
||||
|
||||
<H4><A name="4.13.1">4.13.1</A>) How do I create a
|
||||
<H4><A name="4.11.1">4.11.1</A>) How do I create a
|
||||
serial/auto-incrementing field?</H4>
|
||||
|
||||
<P>PostgreSQL supports a <SMALL>SERIAL</SMALL> data type. It
|
||||
@ -1037,13 +1002,13 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
you need to use <I>pg_dump</I>'s <I>-o</I> option or <SMALL>COPY
|
||||
WITH OIDS</SMALL> option to preserve the <SMALL>OID</SMALL>s.
|
||||
|
||||
<H4><A name="4.13.2">4.13.2</A>) How do I get the value of a
|
||||
<H4><A name="4.11.2">4.11.2</A>) How do I get the value of a
|
||||
<SMALL>SERIAL</SMALL> insert?</H4>
|
||||
|
||||
<P>One approach is 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="#4.13.1">4.13.1</A>, an example in a
|
||||
example table in <A href="#4.11.1">4.11.1</A>, an example in a
|
||||
pseudo-language would look like this:</P>
|
||||
<PRE>
|
||||
new_id = execute("SELECT nextval('person_id_seq')");
|
||||
@ -1066,7 +1031,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
new_id = execute("SELECT currval('person_id_seq')");
|
||||
</PRE>
|
||||
|
||||
<P>Finally, you could use the <A href="#4.14"><SMALL>OID</SMALL></A>
|
||||
<P>Finally, you could use the <A href="#4.12"><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,
|
||||
and the oid value will wrap around when it reaches 4 billion.
|
||||
@ -1074,13 +1039,13 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
available via <I>$sth->{pg_oid_status}</I> after
|
||||
<I>$sth->execute()</I>.</P>
|
||||
|
||||
<H4><A name="4.13.3">4.13.3</A>) Doesn't <I>currval()</I>
|
||||
<H4><A name="4.11.3">4.11.3</A>) Doesn't <I>currval()</I>
|
||||
lead to a race condition with other users?</H4>
|
||||
|
||||
<P>No. <I>currval()</I> returns the current value assigned by your
|
||||
backend, not by all users.</P>
|
||||
|
||||
<H4><A name="4.13.4">4.13.4</A>) Why aren't my sequence numbers
|
||||
<H4><A name="4.11.4">4.11.4</A>) Why aren't my sequence numbers
|
||||
reused on transaction abort? Why are there gaps in the numbering of
|
||||
my sequence/SERIAL column?</H4>
|
||||
|
||||
@ -1089,7 +1054,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
completes. This causes gaps in numbering from aborted
|
||||
transactions.</P>
|
||||
|
||||
<H4><A name="4.14">4.14</A>) What is an <SMALL>OID</SMALL>? What is
|
||||
<H4><A name="4.12">4.12</A>) What is an <SMALL>OID</SMALL>? What is
|
||||
a <SMALL>TID</SMALL>?</H4>
|
||||
|
||||
<P>Every row that is created in PostgreSQL gets a unique
|
||||
@ -1112,7 +1077,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
are modified or reloaded. They are used by index entries to point
|
||||
to physical rows.</P>
|
||||
|
||||
<H4><A name="4.15">4.15</A>) What is the meaning of some of the
|
||||
<H4><A name="4.13">4.13</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
|
||||
@ -1141,7 +1106,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
<P>A list of general database terms can be found at: <A href=
|
||||
"http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary/glossary.html">http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary/glossary.html</A></P>
|
||||
|
||||
<H4><A name="4.16">4.16</A>) Why do I get the error <I>"ERROR:
|
||||
<H4><A name="4.14">4.14</A>) Why do I get the error <I>"ERROR:
|
||||
Memory exhausted in AllocSetAlloc()"</I>?</H4>
|
||||
|
||||
<P>You probably have run out of virtual memory on your system,
|
||||
@ -1160,12 +1125,12 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
backend is returning too much data, try it before starting the
|
||||
client.
|
||||
|
||||
<H4><A name="4.17">4.17</A>) How do I tell what PostgreSQL version
|
||||
<H4><A name="4.15">4.15</A>) How do I tell what PostgreSQL version
|
||||
I am running?</H4>
|
||||
|
||||
<P>From <I>psql</I>, type <CODE>SELECT version();</CODE></P>
|
||||
|
||||
<H4><A name="4.18">4.18</A>) Why does my large-object operations
|
||||
<H4><A name="4.16">4.16</A>) Why does my large-object operations
|
||||
get <I>"invalid large obj descriptor"</I>?</H4>
|
||||
|
||||
<P>You need to put <CODE>BEGIN WORK</CODE> and <CODE>COMMIT</CODE>
|
||||
@ -1181,7 +1146,7 @@ BYTEA bytea variable-length byte array (null-byte 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="4.19">4.19</A>) How do I create a column that will
|
||||
<H4><A name="4.17">4.17</A>) How do I create a column that will
|
||||
default to the current time?</H4>
|
||||
|
||||
<P>Use <I>CURRENT_TIMESTAMP</I>:</P>
|
||||
@ -1190,7 +1155,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
</CODE>
|
||||
</PRE>
|
||||
|
||||
<H4><A name="4.20">4.20</A>) Why are my subqueries using
|
||||
<H4><A name="4.18">4.18</A>) Why are my subqueries using
|
||||
<CODE><SMALL>IN</SMALL></CODE> so slow?</H4>
|
||||
|
||||
<P>In versions prior to 7.4, subqueries were joined to outer queries
|
||||
@ -1214,7 +1179,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
sophisticated join techniques as normal queries, and is prefered
|
||||
to using <CODE>EXISTS</CODE>.
|
||||
|
||||
<H4><A name="4.21">4.21</A>) How do I perform an outer join?</H4>
|
||||
<H4><A name="4.19">4.19</A>) How do I perform an outer join?</H4>
|
||||
|
||||
<P>PostgreSQL supports outer joins using the SQL standard syntax.
|
||||
Here are two examples:</P>
|
||||
@ -1254,7 +1219,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
ORDER BY col1
|
||||
</PRE>
|
||||
|
||||
<H4><A name="4.22">4.22</A>) How do I perform queries using
|
||||
<H4><A name="4.20">4.20</A>) How do I perform queries using
|
||||
multiple databases?</H4>
|
||||
|
||||
<P>There is no way to query a database other than the current one.
|
||||
@ -1266,7 +1231,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
connections to different databases and merge the results on the
|
||||
client side.</P>
|
||||
|
||||
<H4><A name="4.23">4.23</A>) How do I return multiple rows or
|
||||
<H4><A name="4.21">4.21</A>) How do I return multiple rows or
|
||||
columns from a function?</H4>
|
||||
|
||||
<P>In 7.3, you can easily return multiple rows or columns from a
|
||||
@ -1274,7 +1239,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
<a href="http://techdocs.postgresql.org/guides/SetReturningFunctions">
|
||||
http://techdocs.postgresql.org/guides/SetReturningFunctions</a>.
|
||||
|
||||
<H4><A name="4.24">4.24</A>) Why can't I reliably create/drop
|
||||
<H4><A name="4.22">4.22</A>) Why can't I reliably create/drop
|
||||
temporary tables in PL/PgSQL functions?</H4>
|
||||
<P>PL/PgSQL caches function contents, and an unfortunate side effect
|
||||
is that if a PL/PgSQL function accesses a temporary table, and that
|
||||
@ -1284,7 +1249,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
|
||||
<SMALL>EXECUTE</SMALL> for temporary table access in PL/PgSQL. This
|
||||
will cause the query to be reparsed every time.</P>
|
||||
|
||||
<H4><A name="4.25">4.25</A>) What encryption options are available?
|
||||
<H4><A name="4.23">4.23</A>) What encryption options are available?
|
||||
</H4>
|
||||
<UL>
|
||||
<LI><I>contrib/pgcrypto</I> contains many encryption functions for
|
||||
|
||||
Loading…
Reference in New Issue
Block a user