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postgresql9.6-docs-9.6.22-1.mga7.noarch.rpm

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><H1
><A
NAME="SQL-CREATETRANSFORM"
></A
>CREATE TRANSFORM</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN84276"
></A
><H2
>Name</H2
>CREATE TRANSFORM&nbsp;--&nbsp;define a new transform</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN84279"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>CREATE [ OR REPLACE ] TRANSFORM FOR <TT
CLASS="REPLACEABLE"
><I
>type_name</I
></TT
> LANGUAGE <TT
CLASS="REPLACEABLE"
><I
>lang_name</I
></TT
> (
    FROM SQL WITH FUNCTION <TT
CLASS="REPLACEABLE"
><I
>from_sql_function_name</I
></TT
> (<TT
CLASS="REPLACEABLE"
><I
>argument_type</I
></TT
> [, ...]),
    TO SQL WITH FUNCTION <TT
CLASS="REPLACEABLE"
><I
>to_sql_function_name</I
></TT
> (<TT
CLASS="REPLACEABLE"
><I
>argument_type</I
></TT
> [, ...])
);</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATETRANSFORM-DESCRIPTION"
></A
><H2
>Description</H2
><P
>   <TT
CLASS="COMMAND"
>CREATE TRANSFORM</TT
> defines a new transform.
   <TT
CLASS="COMMAND"
>CREATE OR REPLACE TRANSFORM</TT
> will either create a new
   transform, or replace an existing definition.
  </P
><P
>   A transform specifies how to adapt a data type to a procedural language.
   For example, when writing a function in PL/Python using
   the <TT
CLASS="TYPE"
>hstore</TT
> type, PL/Python has no prior knowledge how to
   present <TT
CLASS="TYPE"
>hstore</TT
> values in the Python environment.  Language
   implementations usually default to using the text representation, but that
   is inconvenient when, for example, an associative array or a list would be
   more appropriate.
  </P
><P
>   A transform specifies two functions:
   <P
></P
></P><UL
><LI
><P
>      A <SPAN
CLASS="QUOTE"
>"from SQL"</SPAN
> function that converts the type from the SQL
      environment to the language.  This function will be invoked on the
      arguments of a function written in the language.
     </P
></LI
><LI
><P
>      A <SPAN
CLASS="QUOTE"
>"to SQL"</SPAN
> function that converts the type from the
      language to the SQL environment.  This function will be invoked on the
      return value of a function written in the language.
     </P
></LI
></UL
><P>
   It is not necessary to provide both of these functions.  If one is not
   specified, the language-specific default behavior will be used if
   necessary.  (To prevent a transformation in a certain direction from
   happening at all, you could also write a transform function that always
   errors out.)
  </P
><P
>   To be able to create a transform, you must own and
   have <TT
CLASS="LITERAL"
>USAGE</TT
> privilege on the type, have
   <TT
CLASS="LITERAL"
>USAGE</TT
> privilege on the language, and own and
   have <TT
CLASS="LITERAL"
>EXECUTE</TT
> privilege on the from-SQL and to-SQL
   functions, if specified.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN84307"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="REPLACEABLE"
><I
>type_name</I
></TT
></DT
><DD
><P
>       The name of the data type of the transform.
      </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>lang_name</I
></TT
></DT
><DD
><P
>       The name of the language of the transform.
      </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>from_sql_function_name</I
></TT
>(<TT
CLASS="REPLACEABLE"
><I
>argument_type</I
></TT
> [, ...])</DT
><DD
><P
>       The name of the function for converting the type from the SQL
       environment to the language.  It must take one argument of
       type <TT
CLASS="TYPE"
>internal</TT
> and return type <TT
CLASS="TYPE"
>internal</TT
>.  The
       actual argument will be of the type for the transform, and the function
       should be coded as if it were.  (But it is not allowed to declare an
       SQL-level function returning <TT
CLASS="TYPE"
>internal</TT
> without at
       least one argument of type <TT
CLASS="TYPE"
>internal</TT
>.)  The actual return
       value will be something specific to the language implementation.
      </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>to_sql_function_name</I
></TT
>(<TT
CLASS="REPLACEABLE"
><I
>argument_type</I
></TT
> [, ...])</DT
><DD
><P
>       The name of the function for converting the type from the language to
       the SQL environment.  It must take one argument of type
       <TT
CLASS="TYPE"
>internal</TT
> and return the type that is the type for the
       transform.  The actual argument value will be something specific to the
       language implementation.
      </P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATETRANSFORM-NOTES"
></A
><H2
>Notes</H2
><P
>   Use <A
HREF="sql-droptransform.html"
>DROP TRANSFORM</A
> to remove transforms.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATETRANSFORM-EXAMPLES"
></A
><H2
>Examples</H2
><P
>   To create a transform for type <TT
CLASS="TYPE"
>hstore</TT
> and language
   <TT
CLASS="LITERAL"
>plpythonu</TT
>, first set up the type and the language:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TYPE hstore ...;

CREATE LANGUAGE plpythonu ...;</PRE
><P>
   Then create the necessary functions:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION hstore_to_plpython(val internal) RETURNS internal
LANGUAGE C STRICT IMMUTABLE
AS ...;

CREATE FUNCTION plpython_to_hstore(val internal) RETURNS hstore
LANGUAGE C STRICT IMMUTABLE
AS ...;</PRE
><P>
   And finally create the transform to connect them all together:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TRANSFORM FOR hstore LANGUAGE plpythonu (
    FROM SQL WITH FUNCTION hstore_to_plpython(internal),
    TO SQL WITH FUNCTION plpython_to_hstore(internal)
);</PRE
><P>
   In practice, these commands would be wrapped up in extensions.
  </P
><P
>   The <TT
CLASS="FILENAME"
>contrib</TT
> section contains a number of extensions
   that provide transforms, which can serve as real-world examples.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATETRANSFORM-COMPAT"
></A
><H2
>Compatibility</H2
><P
>   This form of <TT
CLASS="COMMAND"
>CREATE TRANSFORM</TT
> is a
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> extension.  There is a <TT
CLASS="COMMAND"
>CREATE
   TRANSFORM</TT
> command in the <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> standard, but it
   is for adapting data types to client languages.  That usage is not supported
   by <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATETRANSFORM-SEEALSO"
></A
><H2
>See Also</H2
><P
>   <A
HREF="sql-createfunction.html"
>CREATE FUNCTION</A
>,
   <A
HREF="sql-createlanguage.html"
>CREATE LANGUAGE</A
>,
   <A
HREF="sql-createtype.html"
>CREATE TYPE</A
>,
   <A
HREF="sql-droptransform.html"
>DROP TRANSFORM</A
>
  </P
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