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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: Mon Jan 31 20:35:58 EST 2005</P> |
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<P>Last updated: Mon Jan 31 20:41:21 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>) |
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@ -74,8 +74,7 @@ |
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<A href="#4.2">4.2</A>) How do I find out what tables, indexes, |
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databases, and users are defined? How do I see the queries used |
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by <I>psql</I> to display them?<BR> |
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<A href="#4.3">4.3</A>) How do you remove a column from a |
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table, or change its data type?<BR> |
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<A href="#4.3">4.3</A>) How do you change a column's data type?<BR> |
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<A href="#4.4">4.4</A>) What is the maximum size for a row, a |
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table, and a database?<BR> |
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<A href="#4.5">4.5</A>) How much database disk space is required |
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@ -645,28 +644,15 @@ |
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database.</P> |
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<P>There are also system tables beginning with <I>pg_</I> that describe |
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these too. Use <I>psql -l</I> will list all databases.</P> |
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these too.</P> |
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<P>Use <I>psql -l</I> will list all databases.</P> |
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<P>Also try the file <I>pgsql/src/tutorial/syscat.source</I>. It |
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illustrates many of the <SMALL>SELECT</SMALL>s needed to get |
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information from the database system tables.</P> |
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<H4><A name="4.3">4.3</A>) How do you remove a column from a |
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table, or change its data type?</H4> |
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<P><SMALL>DROP COLUMN</SMALL> functionality was added in release 7.3 |
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with <SMALL>ALTER TABLE DROP COLUMN</SMALL>. In earlier versions, |
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you can do this:</P> |
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<PRE> |
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BEGIN; |
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LOCK TABLE old_table; |
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SELECT ... -- select all columns but the one you want to remove |
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INTO TABLE new_table |
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FROM old_table; |
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DROP TABLE old_table; |
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ALTER TABLE new_table RENAME TO old_table; |
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COMMIT; |
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</PRE> |
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<H4><A name="4.3">4.3</A>) How do you change a column's data type?</H4> |
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<P>Changing the data type of a column can be done easily in 8.0 |
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and later with <SMALL>ALTER TABLE ALTER COLUMN TYPE</SMALL>. |
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