Last updated: Sat Jan 29 23:25:05 EST 2005
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
The most recent version of this document can be viewed at http://www.postgresql.org/files/documentation/faqs/FAQ.html.
Platform-specific questions are answered at http://www.postgresql.org/docs/faq/.
PostgreSQL is pronounced Post-Gres-Q-L.
PostgreSQL is an enhancement of the POSTGRES database management system (and is still sometimes reffered to as simply "Postgres"), a next-generation DBMS research prototype. While PostgreSQL retains the powerful data model and rich data types of POSTGRES, it replaces the PostQuel query language with an extended subset of SQL. PostgreSQL is free and the complete source is available.
PostgreSQL development is performed by a team of developers who all subscribe to the PostgreSQL development mailing list. The current coordinator is Marc G. Fournier (scrappy@PostgreSQL.org). (See section 1.6 on how to join). This team is now responsible for all development of PostgreSQL. It is a community project and is not controlled by any company. To get involved, see the developer's FAQ at http://www.postgresql.org/files/documentation/faqs/FAQ_DEV.html
The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many others have contributed to the porting, testing, debugging, and enhancement of the code. The original Postgres code, from which PostgreSQL is derived, was the effort of many graduate students, undergraduate students, and staff programmers working under the direction of Professor Michael Stonebraker at the University of California, Berkeley.
The original name of the software at Berkeley was Postgres. When SQL functionality was added in 1995, its name was changed to Postgres95. The name was changed at the end of 1996 to PostgreSQL.
PostgreSQL is subject to the following COPYRIGHT:
PostgreSQL Data Base Management System
Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group Portions Copyright (c) 1994-6 Regents of the University of California
Permission to use, copy, modify, and distribute this software and its documentation for any purpose, without fee, and without a written agreement is hereby granted, provided that the above copyright notice and this paragraph and the following two paragraphs appear in all copies.
IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
The above is the BSD license, the classic open-source license. It has no restrictions on how the source code may be used. We like it and have no intention of changing it.
In general, any modern Unix-compatible platform should be able to run PostgreSQL. The platforms that had received explicit testing at the time of release are listed in the installation instructions.
Starting with version 8.0, PostgreSQL now runs natively on Microsoft Windows NT-based operating systems like Win2000, WinXP, and Win2003. A prepackaged installer is available at http://pgfoundry.org/projects/pginstaller. MSDOS-based versions of Windows (Win95, Win98, WinMe) can run PostgreSQL using Cygwin.
There is also a Novell Netware 6 port at http://forge.novell.com, and an OS/2 (eComStation) version at http://hobbes.nmsu.edu/cgi-bin/h-search?sh=1&button=Search&key=postgreSQL&stype=all&sort=type&dir=%2F.
The primary anonymous ftp site for PostgreSQL is ftp://ftp.PostgreSQL.org/pub. For mirror sites, see our main web site.
The main mailing list is: pgsql-general@PostgreSQL.org. It is available for discussion of matters pertaining to PostgreSQL. To subscribe, send mail with the following lines in the body (not the subject line):
subscribe
end
to pgsql-general-request@PostgreSQL.org.
There is also a digest list available. To subscribe to this list, send email to: pgsql-general-digest-request@PostgreSQL.org with a body of:
subscribe
end
Digests are sent out to members of this list whenever the main list
has received around 30k of messages.
The bugs mailing list is available. To subscribe to this list, send email to pgsql-bugs-request@PostgreSQL.org with a body of:
subscribe
end
There is also a developers discussion mailing list available. To
subscribe to this list, send email to pgsql-hackers-request@PostgreSQL.org
with a body of:
subscribe
end
Additional mailing lists and information about PostgreSQL can be found via the PostgreSQL WWW home page at:
http://www.PostgreSQL.org
The major IRC channel is #postgresql on Freenode
(irc.freenode.net). To connect you can use the Unix
command irc -c '#postgresql' "$USER" irc.freenode.net
or use any of the other popular IRC clients. A Spanish one also exists
on the same network, (#postgresql-es), and a French one,
(#postgresqlfr). There is also a PostgreSQL channel on EFNet.
A list of commercial support companies is available at http://techdocs.postgresql.org/companies.php.
The latest release of PostgreSQL is version 8.0.0.
We plan to have major releases every six to eight months.
Several manuals, manual pages, and some small test examples are included in the distribution. See the /doc directory. You can also browse the manuals online at http://www.PostgreSQL.org/docs.
There are two PostgreSQL books available online at http://www.PostgreSQL.org/docs/awbook.html and http://www.commandprompt.com/ppbook/. There is a list of PostgreSQL books available for purchase at http://techdocs.PostgreSQL.org/techdocs/bookreviews.php. There is also a collection of PostgreSQL technical articles at http://techdocs.PostgreSQL.org/.
The command line client program psql has some \d commands to show information about types, operators, functions, aggregates, etc. - use \? to display the available commands.
Our web site contains even more documentation.
PostgreSQL supports an extended subset of SQL-92. See our TODO list for known bugs, missing features, and future plans.
The PostgreSQL book at http://www.PostgreSQL.org/docs/awbook.html teaches SQL. There is another PostgreSQL book at http://www.commandprompt.com/ppbook. There is a nice tutorial at http://www.intermedia.net/support/sql/sqltut.shtm, at http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM, and at http://sqlcourse.com.
Another one is "Teach Yourself SQL in 21 Days, Second Edition" at http://members.tripod.com/er4ebus/sql/index.htm
Many of our users like The Practical SQL Handbook, Bowman, Judith S., et al., Addison-Wesley. Others like The Complete Reference SQL, Groff et al., McGraw-Hill.
First, download the latest source and read the PostgreSQL Developers documentation on our web site, or in the distribution. Second, subscribe to the pgsql-hackers and pgsql-patches mailing lists. Third, submit high quality patches to pgsql-patches.
There are about a dozen people who have commit privileges to the PostgreSQL CVS archive. They each have submitted so many high-quality patches that it was impossible for the existing committers to keep up, and we had confidence that patches they committed were of high quality.
Visit the PostgreSQL bug form at http://www.postgresql.org/support/submitbug.
Also check out our ftp site ftp://ftp.PostgreSQL.org/pub to see if there is a more recent PostgreSQL version or patches.
There are several ways of measuring software: features, performance, reliability, support, and price.
PostgreSQL has had a first-class infrastructure since we started in 1996. This is all thanks to Marc Fournier, who has created and managed this infrastructure over the years.
Quality infrastructure is very important to an open-source project. It prevents disruptions that can greatly delay forward movement of the project.
Of course, this infrastructure is not cheap. There are a variety of monthly and one-time expenses that are required to keep it going. If you or your company has money it can donate to help fund this effort, please go to http://store.pgsql.com/shopping/ and make a donation.
Although the web page mentions PostgreSQL, Inc, the "contributions" item is solely to support the PostgreSQL project and does not fund any specific company. If you prefer, you can also send a check to the contact address.
Also, if you have a success story about PostgreSQL, please email it to our advocacy list at pgsql-advocacy@postgresql.org.
The PostgreSQL install includes only the C and embedded C interfaces. All other interfaces are independent projects that are downloaded separately; being separate allows them to have their own release schedule and development teams.
Some programming languages like PHP include an interface to PostgreSQL. Interfaces for languages like Perl, TCL, Python, and many others are available at http://gborg.postgresql.org in the Drivers/Interfaces section and via Internet search.
A nice introduction to Database-backed Web pages can be seen at: http://www.webreview.com
For Web integration, PHP is an excellent interface. It is at http://www.php.net.
For complex cases, many use the Perl interface and CGI.pm or mod_perl.
Yes, there are several graphical interfaces to PostgreSQL available. These include PgAccess http://www.pgaccess.org), pgAdmin III (http://www.pgadmin.org, RHDB Admin (http://sources.redhat.com/rhdb/ ), TORA (http://www.globecom.net/tora/, partly commercial), and Rekall ( http://www.rekallrevealed.org/). There is also PhpPgAdmin ( http://phppgadmin.sourceforge.net/ ), a web-based interface to PostgreSQL.
See http://techdocs.postgresql.org/guides/GUITools for a more detailed list.
Specify the --prefix option when running configure.
By default, PostgreSQL only allows connections from the local machine using Unix domain sockets or TCP/IP connections. Other machines will not be able to connect unless you modify listen_addresses in the postgresql.conf and enable host-based authentication by modifying the file $PGDATA/pg_hba.conf accordingly.
Certainly, indexes can speed up queries. The EXPLAIN ANALYZE command allows you to see how PostgreSQL is interpreting your query, and which indexes are being used.
If you are doing many INSERTs, consider doing them in a large batch using the COPY command. This is much faster than individual INSERTS. Second, statements not in a BEGIN WORK/COMMIT transaction block are considered to be in their own transaction. Consider performing several statements in a single transaction block. This reduces the transaction overhead. Also, consider dropping and recreating indexes when making large data changes.
There are several tuning options in the Administration Guide/Server Run-time Environment/Run-time Configuration. You can disable fsync() by using fsync option. This will prevent fsync()s from flushing to disk after every transaction.
You can use the shared_buffers option to increase the number of shared memory buffers used by the backend processes. If you make this parameter too high, the postmaster may not start because you have exceeded your kernel's limit on shared memory space. Each buffer is 8K and the default is 1000 buffers.
You can also use the sort_mem (from PostgreSQL 8.0: work_mem) options to increase the maximum amount of memory used by the backend processes for each temporary sort. The default is 1024 (i.e. 1MB).
You can also use the CLUSTER command to group data in tables to match an index. See the CLUSTER manual page for more details.
PostgreSQL has several features that report status information that can be valuable for debugging purposes.
First, by running configure with the --enable-cassert option, many assert()s monitor the progress of the backend and halt the program when something unexpected occurs.
Both postmaster and postgres have several debug options available. First, whenever you start postmaster, make sure you send the standard output and error to a log file, like:
cd /usr/local/pgsql
./bin/postmaster >server.log 2>&1 &
This will put a server.log file in the top-level PostgreSQL directory. This file contains useful information about problems or errors encountered by the server. Postmaster has a -d option that allows even more detailed information to be reported. The -d option takes a number that specifies the debug level. Be warned that high debug level values generate large log files.
If postmaster is not running, you can actually run the postgres backend from the command line, and type your SQL statement directly. This is recommended only for debugging purposes. Note that a newline terminates the query, not a semicolon. If you have compiled with debugging symbols, you can use a debugger to see what is happening. Because the backend was not started from postmaster, it is not running in an identical environment and locking/backend interaction problems may not be duplicated.
If postmaster is running, start psql in one
window, then find the PID of the postgres
process used by psql using SELECT pg_backend_pid().
Use a debugger to attach to the postgres PID.
You can set breakpoints in the debugger and issue queries from
psql. If you are debugging postgres startup, you can
set PGOPTIONS="-W n", then start psql. This will cause startup
to delay for n seconds so you can attach to the process with
the debugger, set any breakpoints, and continue through the startup
sequence.
There are several log_* server configuration variables
that enable printing of process statistics which can be very useful
for debugging and performance measurements.
You can also compile with profiling to see what functions are taking execution time. The backend profile files will be deposited in the pgsql/data/base/dbname directory. The client profile file will be put in the client's current directory. Linux requires a compile with -DLINUX_PROFILE for proper profiling.
You need to increase postmaster's limit on how many concurrent backend processes it can start.
The default limit is 32 processes. You can increase it by restarting postmaster with a suitable -N value or modifying postgresql.conf.
Note that if you make -N larger than 32, you must also increase -B beyond its default of 64; -B must be at least twice -N, and probably should be more than that for best performance. For large numbers of backend processes, you are also likely to find that you need to increase various Unix kernel configuration parameters. Things to check include the maximum size of shared memory blocks, SHMMAX; the maximum number of semaphores, SEMMNS and SEMMNI; the maximum number of processes, NPROC; the maximum number of processes per user, MAXUPRC; and the maximum number of open files, NFILE and NINODE. The reason that PostgreSQL has a limit on the number of allowed backend processes is so your system won't run out of resources.
This directory contains temporary files generated by the query executor. For example, if a sort needs to be done to satisfy an ORDER BY and the sort requires more space than the backend's -S parameter allows, then temporary files are created here to hold the extra data.
The temporary files are usually deleted automatically, but might remain if a backend crashes during a sort. A stop and restart of the postmaster will remove files from those directories.
The PostgreSQL team makes only small changes between minor releases, so upgrading from 7.2 to 7.2.1 does not require a dump and restore. However, major releases (e.g. from 7.2 to 7.3) often change the internal format of system tables and data files. These changes are often complex, so we don't maintain backward compatability for data files. A dump outputs data in a generic format that can then be loaded in using the new internal format.
In releases where the on-disk format does not change, the pg_upgrade script can be used to upgrade without a dump/restore. The release notes mention whether pg_upgrade is available for the release.
Because PC hardware is mostly compatible, people tend to believe that all PC hardware is of equal quality. It is not. ECC RAM, SCSI, and quality motherboards are more reliable and have better performance than less expensive hardware. PostgreSQL will run on almost any hardware, but if reliability and performance are important it is wise to research your hardware options thoroughly. Our email lists can be used to discuss hardware options and tradeoffs.
See the FETCH manual page, or use SELECT ... LIMIT....
The entire query may have to be evaluated, even if you only want the first few rows. Consider using a query that has an ORDER BY. If there is an index that matches the ORDER BY, PostgreSQL may be able to evaluate only the first few records requested, or the entire query may have to be evaluated until the desired rows have been generated.
To SELECT a random row, use:
SELECT col
FROM tab
ORDER BY random()
LIMIT 1;
Use the \dt command to see tables in psql. For a complete list of commands inside psql you can use \?. Alternatively you can read the source code for psql in file pgsql/src/bin/psql/describe.c, it contains SQL commands that generate the output for psql's backslash commands. You can also start psql with the -E option so it will print out the queries it uses to execute the commands you give. PostgreSQL also provides an SQL compliant INFORMATION SCHEMA interface you can query to get information about the database.
There are also system tables beginning with pg_ that describe these too. Use psql -l will list all databases.
Also try the file pgsql/src/tutorial/syscat.source. It illustrates many of the SELECTs needed to get information from the database system tables.
DROP COLUMN functionality was added in release 7.3 with ALTER TABLE DROP COLUMN. In earlier versions, you can do this:
BEGIN;
LOCK TABLE old_table;
SELECT ... -- select all columns but the one you want to remove
INTO TABLE new_table
FROM old_table;
DROP TABLE old_table;
ALTER TABLE new_table RENAME TO old_table;
COMMIT;
Changing the data type of a column can be done easily in 8.0 and later with ALTER TABLE ALTER COLUMN TYPE.
In earlier releases, do this:
BEGIN;
ALTER TABLE tab ADD COLUMN new_col new_data_type;
UPDATE tab SET new_col = CAST(old_col AS new_data_type);
ALTER TABLE tab DROP COLUMN old_col;
COMMIT;
You might then want to do VACUUM FULL tab to reclaim the disk space used by the expired rows.
These are the limits:
Maximum size for a database? unlimited (32 TB databases exist)
Maximum size for a table? 32 TB
Maximum size for a row? 1.6TB
Maximum size for a field? 1 GB
Maximum number of rows in a table? unlimited
Maximum number of columns in a table? 250-1600 depending on column types
Maximum number of indexes on a table? unlimited
Of course, these are not actually unlimited, but limited to
available disk space and memory/swap space. Performance may suffer
when these values get unusually large.
The maximum table size of 32 TB does not require large file support from the operating system. Large tables are stored as multiple 1 GB files so file system size limits are not important.
The maximum table size and maximum number of columns can be quadrupled by increasing the default block size to 32k.
A PostgreSQL database may require up to five times the disk space to store data from a text file.
As an example, consider a file of 100,000 lines with an integer and text description on each line. Suppose the text string avergages twenty bytes in length. The flat file would be 2.8 MB. The size of the PostgreSQL database file containing this data can be estimated as 6.4 MB:
32 bytes: each row header (approximate)
24 bytes: one int field and one text field
+ 4 bytes: pointer on page to tuple
----------------------------------------
60 bytes per row
The data page size in PostgreSQL is 8192 bytes (8 KB), so:
8192 bytes per page
------------------- = 136 rows per database page (rounded down)
60 bytes per row
100000 data rows
-------------------- = 735 database pages (rounded up)
128 rows per page
735 database pages * 8192 bytes per page = 6,021,120 bytes (6 MB)
Indexes do not require as much overhead, but do contain the data that is being indexed, so they can be large also.
NULLs are stored as bitmaps, so they use very little space.
Indexes are not automatically used by every query. Indexes are only used if the table is larger than a minimum size, and the query selects only a small percentage of the rows in the table. This is because the random disk access caused by an index scan can be slower than a straight read through the table, or sequential scan.
To determine if an index should be used, PostgreSQL must have statistics about the table. These statistics are collected using VACUUM ANALYZE, or simply ANALYZE. Using statistics, the optimizer knows how many rows are in the table, and can better determine if indexes should be used. Statistics are also valuable in determining optimal join order and join methods. Statistics collection should be performed periodically as the contents of the table change.
Indexes are normally not used for ORDER BY or to perform joins. A sequential scan followed by an explicit sort is usually faster than an index scan of a large table.
However, LIMIT combined with ORDER BY often will use an index because only a small portion of the table is returned. In fact, though MAX() and MIN() don't use indexes, it is possible to retrieve such values using an index with ORDER BY and LIMIT:
SELECT col
FROM tab
ORDER BY col [ DESC ]
LIMIT 1;
If you believe the optimizer is incorrect in choosing a
sequential scan, use SET enable_seqscan TO 'off' and
run tests to see if an index scan is indeed faster.
When using wild-card operators such as LIKE or ~, indexes can only be used in certain circumstances:
text_pattern_ops index for such cases that work only
for LIKE indexing.
In pre-8.0 releases, indexes often can not be used unless the data types exactly match the index's column types. This is particularly true of int2, int8, and numeric column indexes.
See the EXPLAIN manual page.
The ~ operator does regular expression matching, and ~* does case-insensitive regular expression matching. The case-insensitive variant of LIKE is called ILIKE.
Case-insensitive equality comparisons are normally expressed as:
SELECT *
FROM tab
WHERE lower(col) = 'abc';
This will not use an standard index. However, if you create a
functional index, it will be used:
CREATE INDEX tabindex ON tab (lower(col));
You test the column with IS NULL and IS NOT NULL.
Type Internal Name Notes -------------------------------------------------- VARCHAR(n) varchar size specifies maximum length, no padding CHAR(n) bpchar blank padded to the specified fixed length TEXT text no specific upper limit on length BYTEA bytea variable-length byte array (null-byte safe) "char" char one character
You will see the internal name when examining system catalogs and in some error messages.
The first four types above are "varlena" types (i.e., the first four bytes on disk are the length, followed by the data). Thus the actual space used is slightly greater than the declared size. However, these data types are also subject to compression or being stored out-of-line by TOAST, so the space on disk might also be less than expected.
VARCHAR(n) is best when storing variable-length strings and it limits how long a string can be. TEXT is for strings of unlimited length, with a maximum of one gigabyte.CHAR(n) is for storing strings that are all the same length. CHAR(n) pads with blanks to the specified length, while VARCHAR(n) only stores the characters supplied. BYTEA is for storing binary data, particularly values that include NULL bytes. All the types described here have similar performance characteristics.
PostgreSQL supports a SERIAL data type. It auto-creates a sequence. For example, this:
CREATE TABLE person (
id SERIAL,
name TEXT
);
is automatically translated into this:
CREATE SEQUENCE person_id_seq;
CREATE TABLE person (
id INT4 NOT NULL DEFAULT nextval('person_id_seq'),
name TEXT
);
See the create_sequence manual page for more information
about sequences. You can also use each row's OID field as a
unique value. However, if you need to dump and reload the database,
you need to use pg_dump's -o option or COPY
WITH OIDS option to preserve the OIDs.
One approach is to retrieve the next SERIAL value from the sequence object with the nextval() function before inserting and then insert it explicitly. Using the example table in 4.11.1, an example in a pseudo-language would look like this:
new_id = execute("SELECT nextval('person_id_seq')");
execute("INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal')");
You would then also have the new value stored in
new_id for use in other queries (e.g., as a foreign
key to the person table). Note that the name of the
automatically created SEQUENCE object will be named
<table>_<serialcolumn>_seq, where
table and serialcolumn are the names of your table
and your SERIAL column, respectively.
Alternatively, you could retrieve the assigned SERIAL value with the currval() function after it was inserted by default, e.g.,
execute("INSERT INTO person (name) VALUES ('Blaise Pascal')");
new_id = execute("SELECT currval('person_id_seq')");
Finally, you could use the OID returned from the INSERT 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. In Perl, using DBI with the DBD::Pg module, the oid value is made available via $sth->{pg_oid_status} after $sth->execute().
No. currval() returns the current value assigned by your backend, not by all users.
To improve concurrency, sequence values are given out to running transactions as needed and are not locked until the transaction completes. This causes gaps in numbering from aborted transactions.
Every row that is created in PostgreSQL gets a unique OID unless created WITHOUT OIDS. OIDs are autotomatically assigned unique 4-byte integers that are unique across the entire installation. However, they overflow at 4 billion, and then the OIDs start being duplicated. PostgreSQL uses OIDs to link its internal system tables together.
To uniquely number columns in user tables, it is best to use SERIAL rather than OIDs because SERIAL sequences are unique only within a single table. and are therefore less likely to overflow. SERIAL8 is available for storing eight-byte sequence values.
TIDs are used to identify specific physical rows with block and offset values. TIDs change after rows are modified or reloaded. They are used by index entries to point to physical rows.
Some of the source code and older documentation use terms that have more common usage. Here are some:
A list of general database terms can be found at: http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary/glossary.html
You probably have run out of virtual memory on your system, or your kernel has a low limit for certain resources. Try this before starting postmaster:
ulimit -d 262144
limit datasize 256m
Depending on your shell, only one of these may succeed, but it will
set your process data segment limit much higher and perhaps allow
the query to complete. This command applies to the current process,
and all subprocesses created after the command is run. If you are
having a problem with the SQL client because the
backend is returning too much data, try it before starting the
client.
From psql, type SELECT version();
You need to put BEGIN WORK and COMMIT
around any use of a large object handle, that is, surrounding
lo_open ... lo_close.
Currently PostgreSQL enforces the rule by closing large object handles at transaction commit. So the first attempt to do anything with the handle will draw invalid large obj descriptor. So code that used to work (at least most of the time) will now generate that error message if you fail to use a transaction.
If you are using a client interface like ODBC you
may need to set auto-commit off.
Use CURRENT_TIMESTAMP:
CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
PostgreSQL supports outer joins using the SQL standard syntax. Here are two examples:
SELECT *
FROM t1 LEFT OUTER JOIN t2 ON (t1.col = t2.col);
or
SELECT *
FROM t1 LEFT OUTER JOIN t2 USING (col);
These identical queries join t1.col to t2.col, and also return any unjoined rows in t1 (those with no match in t2). A RIGHT join would add unjoined rows of t2. A FULL join would return the matched rows plus all unjoined rows from t1 and t2. The word OUTER is optional and is assumed in LEFT, RIGHT, and FULL joins. Ordinary joins are called INNER joins.
In previous releases, outer joins can be simulated using
UNION and NOT IN. For example, when
joining tab1 and tab2, the following query does an
outer join of the two tables:
SELECT tab1.col1, tab2.col2
FROM tab1, tab2
WHERE tab1.col1 = tab2.col1
UNION ALL
SELECT tab1.col1, NULL
FROM tab1
WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2)
ORDER BY col1
There is no way to query a database other than the current one. Because PostgreSQL loads database-specific system catalogs, it is uncertain how a cross-database query should even behave.
contrib/dblink allows cross-database queries using function calls. Of course, a client can make simultaneous connections to different databases and merge the results on the client side.
In 7.3, you can easily return multiple rows or columns from a function, http://techdocs.postgresql.org/guides/SetReturningFunctions.
PL/PgSQL caches function contents, and an unfortunate side effect is that if a PL/PgSQL function accesses a temporary table, and that table is later dropped and recreated, and the function called again, the function will fail because the cached function contents still point to the old temporary table. The solution is to use EXECUTE for temporary table access in PL/PgSQL. This will cause the query to be reparsed every time.
The problem could be a number of things. Try testing your user-defined function in a stand-alone test program first.
Send your extensions to the pgsql-hackers mailing list, and they will eventually end up in the contrib/ subdirectory.
In versions of PostgreSQL beginning with 7.3, table-returning functions are fully supported in C, PL/PgSQL, and SQL. See the Programmer's Guide for more information. An example of a table-returning function defined in C can be found in contrib/tablefunc.
The Makefiles do not have the proper dependencies for include files. You have to do a make clean and then another make. If you are using GCC you can use the --enable-depend option of configure to have the compiler compute the dependencies automatically.