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>   CREATE INDEX
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><H1
>CREATE INDEX</H1
><DIV
CLASS="REFNAMEDIV"
><H2
>Name</H2
>   CREATE INDEX
   &#8212;    Constructs a secondary index
  </DIV
><DIV
CLASS="REFSYNOPSISDIV"
><PRE
CLASS="SYNOPSIS"
>CREATE [ UNIQUE ] INDEX <TT
CLASS="REPLACEABLE"
><I
>index_name</I
></TT
>
    ON <TT
CLASS="REPLACEABLE"
><I
>table</I
></TT
> [ USING <TT
CLASS="REPLACEABLE"
><I
>acc_name</I
></TT
> ]
    ( <TT
CLASS="REPLACEABLE"
><I
>column</I
></TT
> [ <TT
CLASS="REPLACEABLE"
><I
>ops_name</I
></TT
>] [, ...] )
CREATE [ UNIQUE ] INDEX <TT
CLASS="REPLACEABLE"
><I
>index_name</I
></TT
>
    ON <TT
CLASS="REPLACEABLE"
><I
>table</I
></TT
> [ USING <TT
CLASS="REPLACEABLE"
><I
>acc_name</I
></TT
> ]
    ( <TT
CLASS="REPLACEABLE"
><I
>func_name</I
></TT
>( <TT
CLASS="REPLACEABLE"
><I
>column</I
></TT
> [, ... ]) <TT
CLASS="REPLACEABLE"
><I
>ops_name</I
></TT
> )
  </PRE
><DIV
CLASS="REFSECT2"
><H3
>    Inputs
   </H3
><P
>       <P
></P
></P><DL
><DT
>UNIQUE</DT
><DD
><P
>	   Causes the system to check for
	   duplicate values in the table when the index is created (if data
	   already exist) and each time data is added. Attempts to
	   insert or update non-duplicate data will generate an
	   error.
	  </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>index_name</I
></TT
></DT
><DD
><P
>	   The name of the index to be created.
	  </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>table</I
></TT
></DT
><DD
><P
>	   The name of the table to be indexed.
	  </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>acc_name</I
></TT
></DT
><DD
><P
>	   the name of the access method which is to be used for
	   the index. The default access method is BTREE.
	   Postgres provides three access methods for secondary indexes:
	   <P
></P
></P><DL
><DT
>BTREE</DT
><DD
><P
>	       an implementation of the Lehman-Yao
	       high-concurrency btrees.
	      </P
></DD
><DT
>RTREE</DT
><DD
><P
>implements standard rtrees using Guttman's
	       quadratic split algorithm.
	      </P
></DD
><DT
>HASH</DT
><DD
><P
>	       an implementation of Litwin's linear hashing.
	      </P
></DD
></DL
><P>
	  </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>column</I
></TT
></DT
><DD
><P
>	   The name of a column of the table.
	  </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>ops_name</I
></TT
></DT
><DD
><P
>	   An associated operator class.
	   The following select list returns all ops_names:
	   
<PRE
CLASS="PROGRAMLISTING"
>SELECT am.amname AS acc_name,
       opc.opcname AS ops_name,
       opr.oprname AS ops_comp
    FROM pg_am am, pg_amop amop,
         pg_opclass opc, pg_operator opr
    WHERE amop.amopid = am.oid AND
          amop.amopclaid = opc.oid AND
          amop.amopopr = opr.oid
    ORDER BY acc_name, ops_name, ops_comp</PRE
>

	  </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>func_name</I
></TT
></DT
><DD
><P
>	   A user-defined function, which returns a value that can
	   be indexed.
	  </P
></DD
></DL
><P>

  </P
></DIV
><DIV
CLASS="REFSECT2"
><H3
>    Outputs
   </H3
><P
>&#13;       <P
></P
></P><DL
><DT
><SPAN
CLASS="RETURNVALUE"
>CREATE</SPAN
></DT
><DD
><P
>	   The message returned if the index is successfully created.
	  </P
></DD
><DT
><SPAN
CLASS="RETURNVALUE"
>ERROR: Cannot create index: 'index_name' already exists.</SPAN
></DT
><DD
><P
>	   This error occurs if it is impossible to create the index.

   </P
></DD
></DL
><P>

  </P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><H2
>   Description
  </H2
><P
>  <B
CLASS="COMMAND"
>CREATE INDEX</B
> constructs an index 
 <TT
CLASS="REPLACEABLE"
><I
>index_name</I
></TT
>.
on the specified
<TT
CLASS="REPLACEABLE"
><I
>table</I
></TT
>.

<BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
>Indexes are primarily used to enhance database performance.
But inappropriate use will result in slower performance.</P
></BLOCKQUOTE
>

  </P
><P
>   In the first syntax shown above, the key fields for the
   index are specified as column names; a column may also have
   an associated operator class. An operator class is used
   to specify the operators to be used for a particular
   index. For example, a btree index on four-byte integers
   would use the <TT
CLASS="LITERAL"
>int4_ops</TT
> class;
   this operator class includes
   comparison functions for four-byte integers. The default
   operator class is the appropriate operator class for that
   field type.
  </P
><P
>    In the second syntax, an index is defined
    on the result of a user-defined function
    <TT
CLASS="REPLACEABLE"
><I
>func_name</I
></TT
> applied
    to one or more attributes of a single class. These functional
    indexes can be used to obtain fast access to data
    based on operators that would normally require some
    transformation to apply them to the base data.
   </P
><DIV
CLASS="REFSECT2"
><H3
>    Notes
   </H3
><P
>    Currently, only the BTREE access method supports multi-column
    indexes. Up to 7 keys may be specified.
   </P
><P
>    Use <B
CLASS="COMMAND"
>DROP INDEX</B
>
    to remove an index.
   </P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><H2
>   Usage
  </H2
><P
>To create a btree index on the field <TT
CLASS="LITERAL"
>title</TT
>
   in the table <TT
CLASS="LITERAL"
>films</TT
>:
  </P
><PRE
CLASS="PROGRAMLISTING"
>CREATE UNIQUE INDEX title_idx
    ON films (title);
  </PRE
></DIV
><DIV
CLASS="REFSECT1"
><H2
>   Compatibility
  </H2
><P
>  </P
><DIV
CLASS="REFSECT2"
><H3
>    SQL92
   </H3
><P
>    CREATE INDEX is a <SPAN
CLASS="PRODUCTNAME"
>Postgres</SPAN
> language extension.
   </P
><P
>    There is no <B
CLASS="COMMAND"
>CREATE INDEX</B
> command in SQL92.
   </P
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