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>11.10. Indexes and Collations</A
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>   An index can support only one collation per index column.
   If multiple collations are of interest, multiple indexes may be needed.
  </P
><P
>   Consider these statements:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TABLE test1c (
    id integer,
    content varchar COLLATE "x"
);

CREATE INDEX test1c_content_index ON test1c (content);</PRE
><P>
   The index automatically uses the collation of the
   underlying column.  So a query of the form
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT * FROM test1c WHERE content &gt; <TT
CLASS="REPLACEABLE"
><I
>constant</I
></TT
>;</PRE
><P>
   could use the index, because the comparison will by default use the
   collation of the column.  However, this index cannot accelerate queries
   that involve some other collation.  So if queries of the form, say,
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT * FROM test1c WHERE content &gt; <TT
CLASS="REPLACEABLE"
><I
>constant</I
></TT
> COLLATE "y";</PRE
><P>
   are also of interest, an additional index could be created that supports
   the <TT
CLASS="LITERAL"
>"y"</TT
> collation, like this:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE INDEX test1c_content_y_index ON test1c (content COLLATE "y");</PRE
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文件操作 - indexes-collations.html

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