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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 > )
@@ -26,7 +26,7 @@ <H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
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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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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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-
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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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+
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< HR >
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< H2 align ="center "> General Questions</ H2 >
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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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< 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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+
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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 @@ <H3><A name="4.8">4.8</A>) How do I perform regular expression
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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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-
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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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+
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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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< 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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+
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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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</ HTML >
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