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Bruce Momjian
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doc/FAQ
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@ -67,14 +67,14 @@
4.6) What is the maximum size for a row, table, database? 4.6) What is the maximum size for a row, table, database?
4.7) How much database disk space is required to store data from a 4.7) How much database disk space is required to store data from a
typical text file? typical text file?
4.8) How do I find out what indices or operations are defined in the 4.8) How do I find out what tables or indexes are defined in the
database? database?
4.9) My queries are slow or don't make use of the indexes. Why? 4.9) My queries are slow or don't make use of the indexes. Why?
4.10) How do I see how the query optimizer is evaluating my query? 4.10) How do I see how the query optimizer is evaluating my query?
4.11) What is an R-tree index? 4.11) What is an R-tree index?
4.12) What is Genetic Query Optimization? 4.12) What is the Genetic Query Optimizer?
4.13) How do I do regular expression searches and case-insensitive 4.13) How do I perform regular expression searches and
regular expression searches? case-insensitive regular expression searches?
4.14) In a query, how do I detect if a field is NULL? 4.14) In a query, how do I detect if a field is NULL?
4.15) What is the difference between the various character types? 4.15) What is the difference between the various character types?
4.16.1) How do I create a serial/auto-incrementing field? 4.16.1) How do I create a serial/auto-incrementing field?
@ -90,7 +90,7 @@
Why? Why?
4.22) How do I create a column that will default to the current time? 4.22) How do I create a column that will default to the current time?
4.23) Why are my subqueries using IN so slow? 4.23) Why are my subqueries using IN so slow?
4.24) How do I do an outer join? 4.24) How do I perform an outer join?
Extending PostgreSQL Extending PostgreSQL
@ -677,8 +677,7 @@ Maximum number of indexes on a table? unlimited
Indexes do not require as much overhead, but do contain the data that Indexes do not require as much overhead, but do contain the data that
is being indexed, so they can be large also. is being indexed, so they can be large also.
4.8) How do I find out what indices or operations are defined in the 4.8) How do I find out what tables or indexes are defined in the database?
database?
psql has a variety of backslash commands to show such information. Use psql has a variety of backslash commands to show such information. Use
\? to see them. \? to see them.
@ -739,21 +738,19 @@ Maximum number of indexes on a table? unlimited
extending R-trees requires a bit of work and we don't currently have extending R-trees requires a bit of work and we don't currently have
any documentation on how to do it. any documentation on how to do it.
4.12) What is Genetic Query Optimization? 4.12) What is the Genetic Query Optimizer?
The GEQO module speeds query optimization when joining many tables by The GEQO module speeds query optimization when joining many tables by
means of a Genetic Algorithm (GA). It allows the handling of large means of a Genetic Algorithm (GA). It allows the handling of large
join queries through nonexhaustive search. join queries through nonexhaustive search.
4.13) How do I do regular expression searches and case-insensitive regular 4.13) How do I perform regular expression searches and case-insensitive
expression searches? regular expression searches?
The ~ operator does regular expression matching, and ~* does The ~ operator does regular expression matching, and ~* does
case-insensitive regular expression matching. There is no case-insensitive regular expression matching. The case-insensitive
case-insensitive variant of the LIKE operator, but you can get the variant of LIKE is called ILIKE.
effect of case-insensitive LIKE with this:
WHERE lower(textfield) LIKE lower(pattern)
4.14) In a query, how do I detect if a field is NULL? 4.14) In a query, how do I detect if a field is NULL?
You test the column with IS NULLIS NOT NULL. You test the column with IS NULLIS NOT NULL.
@ -893,13 +890,9 @@ BYTEA bytea variable-length byte array (null-safe)
Depending on your shell, only one of these may succeed, but it will Depending on your shell, only one of these may succeed, but it will
set your process data segment limit much higher and perhaps allow the set your process data segment limit much higher and perhaps allow the
query to complete. This command applies to the current process, and query to complete. This command applies to the current process, and
all subprocessesHTML & CSS specifications are available from all subprocesses created after the command is run. If you are having a
http://www.w3.org/ To learn more about Tidy see problem with the SQL client because the backend is returning too much
http://www.w3.org/People/Raggett/tidy/ Please send bug reports to Dave data, try it before starting the client.
Raggett care of Lobby your company to join W3C, see
http://www.w3.org/Consortium created after the command is run. If you
are having a problem with the SQL client because the backend is
returning too much data, try it before starting the client.
4.20) How do I tell what PostgreSQL version I am running? 4.20) How do I tell what PostgreSQL version I am running?
@ -940,7 +933,7 @@ SELECT *
We hope to fix this limitation in a future release. We hope to fix this limitation in a future release.
4.24) How do I do an outer join? 4.24) How do I perform an outer join?
PostgreSQL 7.1 and later supports outer joins using the SQL standard PostgreSQL 7.1 and later supports outer joins using the SQL standard
syntax. Here are two examples: syntax. Here are two examples:

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doc/src/FAQ/FAQ.html
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@ -103,15 +103,15 @@
database?<BR> database?<BR>
<A href="#4.7">4.7</A>) How much database disk space is required <A href="#4.7">4.7</A>) How much database disk space is required
to store data from a typical text file?<BR> to store data from a typical text file?<BR>
<A href="#4.8">4.8</A>) How do I find out what indices or <A href="#4.8">4.8</A>) How do I find out what tables or
operations are defined in the database?<BR> indexes are defined in the database?<BR>
<A href="#4.9">4.9</A>) My queries are slow or don't make use of <A href="#4.9">4.9</A>) My queries are slow or don't make use of
the indexes. Why?<BR> the indexes. Why?<BR>
<A href="#4.10">4.10</A>) How do I see how the query optimizer is <A href="#4.10">4.10</A>) How do I see how the query optimizer is
evaluating my query?<BR> evaluating my query?<BR>
<A href="#4.11">4.11</A>) What is an R-tree index?<BR> <A href="#4.11">4.11</A>) What is an R-tree index?<BR>
<A href="#4.12">4.12</A>) What is Genetic Query Optimization?<BR> <A href="#4.12">4.12</A>) What is the Genetic Query Optimizer?<BR>
<A href="#4.13">4.13</A>) How do I do regular expression searches <A href="#4.13">4.13</A>) How do I perform regular expression searches
and case-insensitive regular expression searches?<BR> and case-insensitive regular expression searches?<BR>
<A href="#4.14">4.14</A>) In a query, how do I detect if a field <A href="#4.14">4.14</A>) In a query, how do I detect if a field
is <SMALL>NULL</SMALL>?<BR> is <SMALL>NULL</SMALL>?<BR>
@ -137,7 +137,7 @@
default to the current time?<BR> default to the current time?<BR>
<A href="#4.23">4.23</A>) Why are my subqueries using <A href="#4.23">4.23</A>) Why are my subqueries using
<CODE><SMALL>IN</SMALL></CODE> so slow?<BR> <CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
<A href="#4.24">4.24</A>) How do I do an <I>outer</I> join?<BR> <A href="#4.24">4.24</A>) How do I perform an <I>outer</I> join?<BR>
<CENTER> <CENTER>
@ -873,8 +873,8 @@ Maximum number of indexes on a table? unlimited
<P>Indexes do not require as much overhead, but do contain the data <P>Indexes do not require as much overhead, but do contain the data
that is being indexed, so they can be large also.</P> that is being indexed, so they can be large also.</P>
<H4><A name="4.8">4.8</A>) How do I find out what indices or <H4><A name="4.8">4.8</A>) How do I find out what tables or
operations are defined in the database?</H4> indexes are defined in the database?</H4>
<P><I>psql</I> has a variety of backslash commands to show such <P><I>psql</I> has a variety of backslash commands to show such
information. Use \? to see them.</P> information. Use \? to see them.</P>
@ -943,25 +943,21 @@ Maximum number of indexes on a table? unlimited
practice, extending R-trees requires a bit of work and we don't practice, extending R-trees requires a bit of work and we don't
currently have any documentation on how to do it.</P> currently have any documentation on how to do it.</P>
<H4><A name="4.12">4.12</A>) What is Genetic Query <H4><A name="4.12">4.12</A>) What is the Genetic Query
Optimization?</H4> Optimizer?</H4>
<P>The <SMALL>GEQO</SMALL> module speeds query optimization when <P>The <SMALL>GEQO</SMALL> module speeds query optimization when
joining many tables by means of a Genetic Algorithm (GA). It allows joining many tables by means of a Genetic Algorithm (GA). It allows
the handling of large join queries through nonexhaustive the handling of large join queries through nonexhaustive
search.</P> search.</P>
<H4><A name="4.13">4.13</A>) How do I do regular expression <H4><A name="4.13">4.13</A>) How do I perform regular expression
searches and case-insensitive regular expression searches?</H4> searches and case-insensitive regular expression searches?</H4>
<P>The <I>~</I> operator does regular expression matching, and <P>The <I>~</I> operator does regular expression matching, and
<I>~*</I> does case-insensitive regular expression matching. There <I>~*</I> does case-insensitive regular expression matching. The
is no case-insensitive variant of the <SMALL>LIKE</SMALL> operator, case-insensitive variant of <SMALL>LIKE</SMALL>
but you can get the effect of case-insensitive <SMALL>LIKE</SMALL> is called <SMALL>ILIKE</SMALL>.</P>
with this:</P>
<PRE>
WHERE lower(textfield) LIKE lower(pattern)
</PRE>
<H4><A name="4.14">4.14</A>) In a query, how do I detect if a field <H4><A name="4.14">4.14</A>) In a query, how do I detect if a field
is <SMALL>NULL</SMALL>?</H4> is <SMALL>NULL</SMALL>?</H4>
@ -1147,11 +1143,7 @@ BYTEA bytea variable-length byte array (null-safe)
Depending on your shell, only one of these may succeed, but it will Depending on your shell, only one of these may succeed, but it will
set your process data segment limit much higher and perhaps allow set your process data segment limit much higher and perhaps allow
the query to complete. This command applies to the current process, the query to complete. This command applies to the current process,
and all subprocessesHTML & CSS specifications are available from http://www.w3.org/ and all subprocesses created after the command is run. If you are
To learn more about Tidy see http://www.w3.org/People/Raggett/tidy/
Please send bug reports to Dave Raggett care of <html-tidy@w3.org>
Lobby your company to join W3C, see http://www.w3.org/Consortium
created after the command is run. If you are
having a problem with the <SMALL>SQL</SMALL> client because the having a problem with the <SMALL>SQL</SMALL> client because the
backend is returning too much data, try it before starting the backend is returning too much data, try it before starting the
client. client.
@ -1212,7 +1204,7 @@ Lobby your company to join W3C, see http://www.w3.org/Consortium
</PRE> </PRE>
We hope to fix this limitation in a future release. We hope to fix this limitation in a future release.
<H4><A name="4.24">4.24</A>) How do I do an <I>outer</I> join?<BR> <H4><A name="4.24">4.24</A>) How do I perform an <I>outer</I> join?<BR>
</H4> </H4>
<P>PostgreSQL 7.1 and later supports outer joins using the SQL <P>PostgreSQL 7.1 and later supports outer joins using the SQL