102102 Why?
103103 4.22) How do I create a column that will default to the current time?
104104 4.23) Why are my subqueries using IN so slow?
105+ 4.24) How do I do an outer join?
105106
106107 Extending PostgreSQL
107108
334335
335336 Features
336337 PostgreSQL has most features present in large commercial
337- DBMS's, like transactions, subselects, triggers, views,and
338- sophisticated locking. We have some features they don't have,
339- like user-defined types, inheritance, rules, and multi-version
340- concurrency control to reduce lock contention. We don't have
341- foreign key referential integrity or outer joins, but are
338+ DBMS's, like transactions, subselects, triggers, views,foreign
339+ key referential integrity, and sophisticated locking. We have
340+ some features they don't have, like user-defined types,
341+ inheritance, rules, and multi-version concurrency control to
342+ reduce lock contention. We don't have outer joins, but are
342343 working on them for our next release.
343344
344345 Performance
395396
396397 2.1) Are there ODBC drivers for PostgreSQL?
397398
398- There are two ODBC drivers available,PostODBC and OpenLink ODBC.
399+ There are two ODBC drivers available,PsqlODBC and OpenLink ODBC.
399400
400- PostODBC is included in the distribution. More information about it
401- can be gotten from:http ://www.insightdist.com/psqlodbc
401+ PsqlODBC is included in the distribution. More information about it
402+ can be gotten from:ftp ://ftp.postgresql.org/pub/odbc/index.html
402403
403404 OpenLink ODBC can be gotten from http://www.openlinksw.com. It works
404405 with their standard ODBC client software so you'll have PostgreSQL
409410 commercial-quality support, but a freeware version will always be
410411 available. Questions to postgres95@openlink.co.uk.
411412
413+ See also the ODBC chapter of the Programmer's Guide.
414+
412415 2.2) What tools are available for hooking PostgreSQL to Web pages?
413416
414417 A nice introduction to Database-backed Web pages can be seen at:
@@ -971,12 +974,9 @@ BYTEA bytea variable-length array of bytes
971974
972975 4.22) How do I create a column that will default to the current time?
973976
974- This way always works :
977+ Use now() :
975978 CREATE TABLE test (x int, modtime timestamp default now() );
976979
977- In releases 7.0 and later, you may use:
978- create table test (x int, modtime timestamp default 'now');
979-
980980 4.23) Why are my subqueries using IN so slow?
981981
982982 Currently, we join subqueries to outer queries by sequential scanning
@@ -992,6 +992,21 @@ BYTEA bytea variable-length array of bytes
992992 WHERE EXISTS (SELECT col2 FROM TAB2 WHERE col1 = col2)
993993
994994 We hope to fix this limitation in a future release.
995+
996+ 4.24) How do I do an outer join?
997+
998+ PostgreSQL does not support outer joins in the current release. They
999+ can be simulated using UNION and NOT IN. For example, when joining
1000+ tab1 and tab2, the following query does an outer join of the two
1001+ tables:
1002+ SELECT tab1.col1, tab2.col2
1003+ FROM tab1, tab2
1004+ WHERE tab1.col1 = tab2.col1
1005+ UNION ALL
1006+ SELECT tab1.col1, NULL
1007+ FROM tab1
1008+ WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2)
1009+ ORDER BY tab1.col1
9951010 _________________________________________________________________
9961011
9971012 Extending PostgreSQL