Frequently Asked Questions (FAQ) for PostgreSQL
- Last updated: Mon Jan 31 21:31:39 EST 2005
+ Last updated: Mon Jan 31 21:35:15 EST 2005
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
4.16) How do I create a column that will default to the current time?
Use CURRENT_TIMESTAMP:
- CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
+ CREATE TABLE test (x int, modtime TIMESTAMP DEFAULT CURRENT_TIMESTAMP );
4.17) How do I perform an outer join?
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
-
4.18) How do I perform queries using multiple databases?
There is no way to query a database other than the current one.
alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
- <P>Last updated: Mon Jan 31 21:31:39 EST 2005</P>
+ <P>Last updated: Mon Jan 31 21:35:15 EST 2005</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)
<P>Use <I>CURRENT_TIMESTAMP</I>:</P>
<PRE>
- CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
+ CREATE TABLE test (x int, modtime TIMESTAMP DEFAULT CURRENT_TIMESTAMP );
</PRE>
<H4><A name="4.17">4.17</A>) How do I perform an outer join?</H4>
<SMALL>RIGHT</SMALL>, and <SMALL>FULL</SMALL> joins. Ordinary joins
are called <SMALL>INNER</SMALL> joins.</P>
- <P>In previous releases, outer joins can be simulated using
- <SMALL>UNION</SMALL> and <SMALL>NOT IN</SMALL>. For example, when
- joining <I>tab1</I> and <I>tab2</I>, the following query does an
- <I>outer</I> join of the two tables:<BR>
- <BR>
- </P>
-<PRE>
- 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
-</PRE>
-
<H4><A name="4.18">4.18</A>) How do I perform queries using
multiple databases?</H4>