diff options
Diffstat (limited to 'doc/src/FAQ/FAQ.html')
| -rw-r--r-- | doc/src/FAQ/FAQ.html | 121 |
1 files changed, 55 insertions, 66 deletions
diff --git a/doc/src/FAQ/FAQ.html b/doc/src/FAQ/FAQ.html index dd5eb71073a..1133ab77d2f 100644 --- a/doc/src/FAQ/FAQ.html +++ b/doc/src/FAQ/FAQ.html @@ -11,7 +11,7 @@ alink="#0000FF"> <H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1> - <P>Last updated: Wed Dec 5 00:41:12 EST 2001</P> + <P>Last updated: Fri Jan 4 00:44:42 EST 2002</P> <P>Current maintainer: Bruce Momjian (<A href= "mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR> @@ -89,57 +89,55 @@ <CENTER> <H2>Operational Questions</H2> </CENTER> - <A href="#4.1">4.1</A>) Why is the system confused about commas, - decimal points, and date formats.<BR> - <A href="#4.2">4.2</A>) What is the exact difference between + <A href="#4.1">4.1</A>) What is the difference between binary cursors and normal cursors?<BR> - <A href="#4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the + <A href="#4.2">4.2</A>) How do I <SMALL>SELECT</SMALL> only the first few rows of a query?<BR> - <A href="#4.4">4.4</A>) How do I get a list of tables or other + <A href="#4.3">4.3</A>) How do I get a list of tables or other things I can see in <I>psql?</I><BR> - <A href="#4.5">4.5</A>) How do you remove a column from a + <A href="#4.4">4.4</A>) How do you remove a column from a table?<BR> - <A href="#4.6">4.6</A>) What is the maximum size for a row, table, + <A href="#4.5">4.5</A>) What is the maximum size for a row, table, database?<BR> - <A href="#4.7">4.7</A>) How much database disk space is required + <A href="#4.6">4.6</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 tables or indexes + <A href="#4.7">4.7</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 + <A href="#4.8">4.8</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 + <A href="#4.9">4.9</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 the Genetic Query Optimizer?<BR> - <A href="#4.13">4.13</A>) How do I perform regular expression + <A href="#4.10">4.10</A>) What is an R-tree index?<BR> + <A href="#4.11">4.11</A>) What is the Genetic Query Optimizer?<BR> + <A href="#4.12">4.12</A>) How do I perform regular expression searches and case-insensitive regular expression searches? How do I use an index for case-insensitive searches?<BR> - <A href="#4.14">4.14</A>) In a query, how do I detect if a field + <A href="#4.13">4.13</A>) In a query, how do I detect if a field is <SMALL>NULL</SMALL>?<BR> - <A href="#4.15">4.15</A>) What is the difference between the + <A href="#4.14">4.14</A>) What is the difference between the various character types?<BR> - <A href="#4.16.1">4.16.1</A>) How do I create a + <A href="#4.15.1">4.15.1</A>) How do I create a serial/auto-incrementing field?<BR> - <A href="#4.16.2">4.16.2</A>) How do I get the value of a + <A href="#4.15.2">4.15.2</A>) How do I get the value of a <SMALL>SERIAL</SMALL> insert?<BR> - <A href="#4.16.3">4.16.3</A>) Don't <I>currval()</I> and + <A href="#4.15.3">4.15.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to a race condition with other users?<BR> - <A href="#4.17">4.17</A>) What is an <SMALL>OID</SMALL>? What is a + <A href="#4.16">4.16</A>) What is an <SMALL>OID</SMALL>? What is a <SMALL>TID</SMALL>?<BR> - <A href="#4.18">4.18</A>) What is the meaning of some of the terms + <A href="#4.17">4.17</A>) What is the meaning of some of the terms used in PostgreSQL?<BR> - <A href="#4.19">4.19</A>) Why do I get the error <I>"ERROR: + <A href="#4.18">4.18</A>) Why do I get the error <I>"ERROR: Memory exhausted in AllocSetAlloc()?"</I><BR> - <A href="#4.20">4.20</A>) How do I tell what PostgreSQL version I + <A href="#4.19">4.19</A>) How do I tell what PostgreSQL version I am running? <BR> - <A href="#4.21">4.21</A>) My large-object operations get + <A href="#4.20">4.20</A>) My large-object operations get <I>invalid large obj descriptor.</I> Why?<BR> - <A href="#4.22">4.22</A>) How do I create a column that will + <A href="#4.21">4.21</A>) How do I create a column that will default to the current time?<BR> - <A href="#4.23">4.23</A>) Why are my subqueries using + <A href="#4.22">4.22</A>) Why are my subqueries using <CODE><SMALL>IN</SMALL></CODE> so slow?<BR> - <A href="#4.24">4.24</A>) How do I perform an outer join?<BR> - <A href="#4.25">4.25</A>) How do I perform queries using multiple databases?<BR> + <A href="#4.23">4.23</A>) How do I perform an outer join?<BR> + <A href="#4.24">4.24</A>) How do I perform queries using multiple databases?<BR> <CENTER> @@ -788,22 +786,13 @@ <H2>Operational Questions</H2> </CENTER> - <H4><A name="4.1">4.1</A>) Why is system confused about commas, - decimal points, and date formats.</H4> - - <P>Check your locale configuration. PostgreSQL uses the locale - setting of the user that ran the <I>postmaster</I> process. There - are postgres and psql <SMALL>SET</SMALL> commands to control the - date format. Set those accordingly for your operating - environment.</P> - - <H4><A name="4.2">4.2</A>) What is the exact difference between + <H4><A name="4.1">4.1</A>) What is the difference between binary cursors and normal cursors?</H4> <P>See the <SMALL>DECLARE</SMALL> manual page for a description.</P> - <H4><A name="4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the + <H4><A name="4.2">4.2</A>) How do I <SMALL>SELECT</SMALL> only the first few rows of a query?</H4> <P>See the <SMALL>FETCH</SMALL> manual page, or use @@ -816,7 +805,7 @@ records requested, or the entire query may have to be evaluated until the desired rows have been generated.</P> - <H4><A name="4.4">4.4</A>) How do I get a list of tables or other + <H4><A name="4.3">4.3</A>) How do I get a list of tables or other things I can see in <I>psql?</I><BR> </H4> @@ -827,7 +816,7 @@ <I>-E</I> option so it will print out the queries it uses to execute the commands you give.</P> - <H4><A name="4.5">4.5</A>) How do you remove a column from a + <H4><A name="4.4">4.4</A>) How do you remove a column from a table?</H4> <P>We do not support <SMALL>ALTER TABLE DROP COLUMN,</SMALL> but do @@ -840,7 +829,7 @@ ALTER TABLE new_table RENAME TO old_table; </PRE> - <H4><A name="4.6">4.6</A>) What is the maximum size for a row, + <H4><A name="4.5">4.5</A>) What is the maximum size for a row, table, database?</H4> <P>These are the limits:</P> @@ -864,7 +853,7 @@ <P>The maximum table size and maximum number of columns can be increased if the default block size is increased to 32k.</P> - <H4><A name="4.7">4.7</A>) How much database disk space is required + <H4><A name="4.6">4.6</A>) How much database disk space is required to store data from a typical text file?<BR> </H4> @@ -897,7 +886,7 @@ <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 tables or indexes + <H4><A name="4.7">4.7</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 @@ -907,7 +896,7 @@ illustrates many of the <SMALL>SELECT</SMALL>s needed to get information from the database system tables.</P> - <H4><A name="4.9">4.9</A>) My queries are slow or don't make use of + <H4><A name="4.8">4.8</A>) My queries are slow or don't make use of the indexes. Why?</H4> <P>PostgreSQL does not automatically maintain statistics. @@ -937,12 +926,12 @@ <I>~</I>(regular expression searches) should start with <I>^.</I></P> - <H4><A name="4.10">4.10</A>) How do I see how the query optimizer + <H4><A name="4.9">4.9</A>) How do I see how the query optimizer is evaluating my query?</H4> <P>See the <SMALL>EXPLAIN</SMALL> manual page.</P> - <H4><A name="4.11">4.11</A>) What is an R-tree index?</H4> + <H4><A name="4.10">4.10</A>) What is an R-tree index?</H4> <P>An R-tree index is used for indexing spatial data. A hash index can't handle range searches. A B-tree index only handles range @@ -967,7 +956,7 @@ 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 the Genetic Query + <H4><A name="4.11">4.11</A>) What is the Genetic Query Optimizer?</H4> <P>The <SMALL>GEQO</SMALL> module speeds query optimization when @@ -975,7 +964,7 @@ the handling of large join queries through nonexhaustive search.</P> - <H4><A name="4.13">4.13</A>) How do I perform regular expression + <H4><A name="4.12">4.12</A>) How do I perform regular expression searches and case-insensitive regular expression searches? How do I use an index for case-insensitive searches?</H4> @@ -999,12 +988,12 @@ CREATE INDEX tabindex on tab (lower(col)); </PRE> - <H4><A name="4.14">4.14</A>) In a query, how do I detect if a field + <H4><A name="4.13">4.13</A>) In a query, how do I detect if a field is <SMALL>NULL</SMALL>?</H4> <P>You test the column with <SMALL>IS NULL</SMALL>IS NOT NULL.</P> - <H4><A name="4.15">4.15</A>) What is the difference between the + <H4><A name="4.14">4.14</A>) What is the difference between the various character types?</H4> <PRE> Type Internal Name Notes @@ -1034,7 +1023,7 @@ BYTEA bytea variable-length byte array (null-safe) binary data, particularly values that include <SMALL>NULL</SMALL> bytes.</P> - <H4><A name="4.16.1">4.16.1</A>) How do I create a + <H4><A name="4.15.1">4.15.1</A>) How do I create a serial/auto-incrementing field?</H4> <P>PostgreSQL supports a <SMALL>SERIAL</SMALL> data type. It @@ -1064,13 +1053,13 @@ BYTEA bytea variable-length byte array (null-safe) <P><A href="http://www.PostgreSQL.org/docs/aw_pgsql_book">Numbering Rows.</A></P> - <H4><A name="4.16.2">4.16.2</A>) How do I get the value of a + <H4><A name="4.15.2">4.15.2</A>) How do I get the value of a <SMALL>SERIAL</SMALL> insert?</H4> <P>One approach is to to retrieve the next <SMALL>SERIAL</SMALL> value from the sequence object with the <I>nextval()</I> function <I>before</I> inserting and then insert it explicitly. Using the - example table in <A href="#4.16.1">4.16.1</A>, that might look like + example table in <A href="#4.15.1">4.15.1</A>, that might look like this in Perl:</P> <PRE> new_id = output of "SELECT nextval('person_id_seq')" @@ -1091,20 +1080,20 @@ BYTEA bytea variable-length byte array (null-safe) INSERT INTO person (name) VALUES ('Blaise Pascal'); new_id = output of "SELECT currval('person_id_seq')"; </PRE> - Finally, you could use the <A href="#4.17"><SMALL>OID</SMALL></A> + Finally, you could use the <A href="#4.16"><SMALL>OID</SMALL></A> returned from the <SMALL>INSERT</SMALL> statement to look up the default value, though this is probably the least portable approach. In Perl, using DBI with Edmund Mergl's DBD::Pg module, the oid value is made available via <I>$sth->{pg_oid_status} after $sth->execute().</I> - <H4><A name="4.16.3">4.16.3</A>) Don't <I>currval()</I> and + <H4><A name="4.15.3">4.15.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to a race condition with other users?</H4> <P>No. Currval() returns the current value assigned by your backend, not by all users.</P> - <H4><A name="4.17">4.17</A>) What is an <SMALL>OID</SMALL>? What is + <H4><A name="4.16">4.16</A>) What is an <SMALL>OID</SMALL>? What is a <SMALL>TID</SMALL>?</H4> <P><SMALL>OID</SMALL>s are PostgreSQL's answer to unique row ids. @@ -1149,7 +1138,7 @@ BYTEA bytea variable-length byte array (null-safe) or reloaded. They are used by index entries to point to physical rows.</P> - <H4><A name="4.18">4.18</A>) What is the meaning of some of the + <H4><A name="4.17">4.17</A>) What is the meaning of some of the terms used in PostgreSQL?</H4> <P>Some of the source code and older documentation use terms that @@ -1178,7 +1167,7 @@ BYTEA bytea variable-length byte array (null-safe) <P>A list of general database terms can be found at: <A href= "http://www.comptechnews.com/~reaster/dbdesign.html">http://www.comptechnews.com/~reaster/dbdesign.html</A></P> - <H4><A name="4.19">4.19</A>) Why do I get the error <I>"ERROR: + <H4><A name="4.18">4.18</A>) Why do I get the error <I>"ERROR: Memory exhausted in AllocSetAlloc()?"</I><BR> </H4> @@ -1198,13 +1187,13 @@ BYTEA bytea variable-length byte array (null-safe) backend is returning too much data, try it before starting the client. - <H4><A name="4.20">4.20</A>) How do I tell what PostgreSQL version + <H4><A name="4.19">4.19</A>) How do I tell what PostgreSQL version I am running?<BR> </H4> <P>From <I>psql,</I> type <CODE>select version();</CODE></P> - <H4><A name="4.21">4.21</A>) My large-object operations get + <H4><A name="4.20">4.20</A>) My large-object operations get <I>invalid large obj descriptor.</I> Why?<BR> </H4> @@ -1221,7 +1210,7 @@ BYTEA bytea variable-length byte array (null-safe) <P>If you are using a client interface like <SMALL>ODBC</SMALL> you may need to set <CODE>auto-commit off.</CODE></P> - <H4><A name="4.22">4.22</A>) How do I create a column that will + <H4><A name="4.21">4.21</A>) How do I create a column that will default to the current time?<BR> </H4> @@ -1231,7 +1220,7 @@ BYTEA bytea variable-length byte array (null-safe) </CODE> </PRE> - <H4><A name="4.23">4.23</A>) Why are my subqueries using + <H4><A name="4.22">4.22</A>) Why are my subqueries using <CODE><SMALL>IN</SMALL></CODE> so slow?<BR> </H4> @@ -1254,7 +1243,7 @@ BYTEA bytea variable-length byte array (null-safe) </PRE> We hope to fix this limitation in a future release. - <H4><A name="4.24">4.24</A>) How do I perform an outer join?<BR> + <H4><A name="4.23">4.23</A>) How do I perform an outer join?<BR> </H4> <P>PostgreSQL 7.1 and later supports outer joins using the SQL @@ -1295,7 +1284,7 @@ BYTEA bytea variable-length byte array (null-safe) ORDER BY col1 </PRE> - <H4><A href="#4.25">4.25</A>) How do I perform queries + <H4><A href="#4.24">4.24</A>) How do I perform queries using multiple databases?</H4> <P>There is no way to query any database except the current one. |