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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 May 30 09:11:03 EDT 2005</P> |
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<P>Last updated: Wed Aug 10 15:29:42 EDT 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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@ -26,7 +26,7 @@ |
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<HR> |
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<H2 align="center">General Questions</H2> |
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<A href="#1.1">1.1</A>) What is PostgreSQL? How is it pronounced?<BR> |
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<A href="#1.1">1.1</A>) What is PostgreSQL? How is it pronounced?<BR> |
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<A href="#1.2">1.2</A>) What is the copyright of PostgreSQL?<BR> |
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<A href="#1.3">1.3</A>) What platforms does PostgreSQL support?<BR> |
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<A href="#1.4">1.4</A>) Where can I get PostgreSQL?<BR> |
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@ -116,7 +116,9 @@ |
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does not exist" errors when accessing temporary tables in PL/PgSQL |
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functions?<BR> |
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<A href="#4.20">4.20</A>) What replication solutions are available?<BR> |
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<A href="#4.21">4.21</A>) Why are my table and column names not |
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recognized in my query?<BR> |
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<HR> |
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@ -124,8 +126,10 @@ |
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<H3><A name="1.1">1.1</A>) What is PostgreSQL? How is it pronounced?</H3> |
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<P>PostgreSQL is pronounced <I>Post-Gres-Q-L</I>, also called just |
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<I>Postgres</I>.</P> |
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<P>PostgreSQL is pronounced <I>Post-Gres-Q-L</I>, and is also sometimes |
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referred to as just <I>Postgres</I>. An audio file is available in |
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<a href="http://www.postgresql.org/files/postgresql.mp3">MP3 format</a> for |
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those would like to hear the pronunciation.</P> |
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<P>PostgreSQL is an object-relational database system that has the |
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features of traditional commercial database systems with |
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@ -613,6 +617,12 @@ table?</TD><TD>unlimited</TD></TR> |
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<P>The maximum table size and maximum number of columns can be |
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quadrupled by increasing the default block size to 32k.</P> |
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<P>One limitation is that indexes can not be created on columns |
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longer than about 2,000 characters. Fortunately, such indexes are |
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rarely needed. Uniqueness is best guaranteed using another column |
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that is an MD5 hash of the long column, and full text indexing |
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allows for searching of words within the column.</P> |
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<H3><A name="4.5">4.5</A>) How much database disk space is required |
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to store data from a typical text file?</H3> |
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@ -740,7 +750,12 @@ table?</TD><TD>unlimited</TD></TR> |
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<PRE> |
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CREATE INDEX tabindex ON tab (lower(col)); |
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</PRE> |
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<P>If the above index is created as <SMALL>UNIQUE</SMALL>, though |
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the column can store upper and lowercase characters, it can not have |
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identical values that differ only in case. To force a particular |
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case to be stored in the column, use a <SMALL>CHECK</SMALL> |
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constraint or a trigger.</P> |
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<H3><A name="4.9">4.9</A>) In a query, how do I detect if a field |
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is <SMALL>NULL</SMALL>? How can I sort on whether a field is <SMALL> |
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NULL</SMALL> or not?</H3> |
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@ -1000,5 +1015,22 @@ length</TD></TR> |
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<P>There are also commercial and hardware-based replication solutions |
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available supporting a variety of replication models.</P> |
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<H3><A name="4.20">4.20</A>) Why are my table and column names not |
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recognized in my query?</H3> |
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<P>The most common cause is the use of double-quotes around table or |
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column names during table creation. When double-quotes are used, |
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table and column names (called identifiers) are stored <a |
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href="http://www.postgresql.org/docs/8.0/static/sql-syntax.html#SQL- |
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SYNTAX-IDENTIFIERS">case-sensitive</a>, meaning you must use |
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double-quotes when referencing the names in a query. Some interfaces, |
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like pgAdmin, automatically double-quote identifiers during table |
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creation. So, for identifiers to be recognized, you must either: |
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<UL> |
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<LI>Avoid double-quoting identifiers when creating tables</LI> |
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<LI>Use only lowercase characters in identifiers</LI> |
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<LI>Double-quote identifiers when referencing them in queries</LI> |
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</UL> |
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</BODY> |
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</HTML> |
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Bruce Momjian
20 years ago