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
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?
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?
4.11) What is an R-tree index?
- 4.12) What is Genetic Query Optimization?
- 4.13) How do I do regular expression searches and case-insensitive
- regular expression searches?
+ 4.12) What is the Genetic Query Optimizer?
+ 4.13) How do I perform regular expression searches and
+ case-insensitive regular expression searches?
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?
4.16.1) How do I create a serial/auto-incrementing field?
Why?
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?
- 4.24) How do I do an outer join?
+ 4.24) How do I perform an outer join?
Extending PostgreSQL
Indexes do not require as much overhead, but do contain the data that
is being indexed, so they can be large also.
- 4.8) How do I find out what indices or operations are defined in the
- database?
+ 4.8) How do I find out what tables or indexes are defined in the database?
psql has a variety of backslash commands to show such information. Use
\? to see them.
extending R-trees requires a bit of work and we don't currently have
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
means of a Genetic Algorithm (GA). It allows the handling of large
join queries through nonexhaustive search.
- 4.13) How do I do regular expression searches and case-insensitive regular
- expression searches?
+ 4.13) How do I perform regular expression searches and case-insensitive
+ regular expression searches?
The ~ operator does regular expression matching, and ~* does
- case-insensitive regular expression matching. There is no
- case-insensitive variant of the LIKE operator, but you can get the
- effect of case-insensitive LIKE with this:
- WHERE lower(textfield) LIKE lower(pattern)
-
+ case-insensitive regular expression matching. The case-insensitive
+ variant of LIKE is called ILIKE.
+
4.14) In a query, how do I detect if a field is NULL?
You test the column with IS NULLIS NOT NULL.
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
query to complete. This command applies to the current process, and
- all subprocessesHTML & CSS specifications are available from
- http://www.w3.org/ To learn more about Tidy see
- http://www.w3.org/People/Raggett/tidy/ Please send bug reports to Dave
- 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.
+ all subprocesses 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?
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
syntax. Here are two examples:
database?<BR>
<A href="#4.7">4.7</A>) How much database disk space is required
to store data from a typical text file?<BR>
- <A href="#4.8">4.8</A>) How do I find out what indices or
- operations are defined in the database?<BR>
+ <A href="#4.8">4.8</A>) How do I find out what tables or
+ indexes are defined in the database?<BR>
<A href="#4.9">4.9</A>) My queries are slow or don't make use of
the indexes. Why?<BR>
<A href="#4.10">4.10</A>) How do I see how the query optimizer is
evaluating my query?<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="#4.13">4.13</A>) How do I do regular expression searches
+ <A href="#4.12">4.12</A>) What is the Genetic Query Optimizer?<BR>
+ <A href="#4.13">4.13</A>) How do I perform regular expression searches
and case-insensitive regular expression searches?<BR>
<A href="#4.14">4.14</A>) In a query, how do I detect if a field
is <SMALL>NULL</SMALL>?<BR>
default to the current time?<BR>
<A href="#4.23">4.23</A>) Why are my subqueries using
<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>
<P>Indexes do not require as much overhead, but do contain the data
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
- operations are defined in the database?</H4>
+ <H4><A name="4.8">4.8</A>) How do I find out what tables or
+ indexes are defined in the database?</H4>
<P><I>psql</I> has a variety of backslash commands to show such
information. Use \? to see them.</P>
practice, extending R-trees requires a bit of work and we don't
currently have any documentation on how to do it.</P>
- <H4><A name="4.12">4.12</A>) What is Genetic Query
- Optimization?</H4>
+ <H4><A name="4.12">4.12</A>) What is the Genetic Query
+ Optimizer?</H4>
<P>The <SMALL>GEQO</SMALL> module speeds query optimization when
joining many tables by means of a Genetic Algorithm (GA). It allows
the handling of large join queries through nonexhaustive
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>
<P>The <I>~</I> operator does regular expression matching, and
- <I>~*</I> does case-insensitive regular expression matching. There
- is no case-insensitive variant of the <SMALL>LIKE</SMALL> operator,
- but you can get the effect of case-insensitive <SMALL>LIKE</SMALL>
- with this:</P>
-<PRE>
- WHERE lower(textfield) LIKE lower(pattern)
-</PRE>
+ <I>~*</I> does case-insensitive regular expression matching. The
+ case-insensitive variant of <SMALL>LIKE</SMALL>
+ is called <SMALL>ILIKE</SMALL>.</P>
<H4><A name="4.14">4.14</A>) In a query, how do I detect if a field
is <SMALL>NULL</SMALL>?</H4>
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 query to complete. This command applies to the current process,
- and all subprocessesHTML & CSS specifications are available from http://www.w3.org/
-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
+ and all subprocesses created after the command is run. If you are
having a problem with the <SMALL>SQL</SMALL> client because the
backend is returning too much data, try it before starting the
client.
</PRE>
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>
<P>PostgreSQL 7.1 and later supports outer joins using the SQL
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