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><DIV
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><H1
CLASS="SECT1"
><A
NAME="FUNCTIONS-BINARYSTRING"
>9.5. Binary String Functions and Operators</A
></H1
><P
> This section describes functions and operators for examining and
manipulating values of type <TT
CLASS="TYPE"
>bytea</TT
>.
</P
><P
> <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> defines some string functions that use
key words, rather than commas, to separate
arguments. Details are in
<A
HREF="functions-binarystring.html#FUNCTIONS-BINARYSTRING-SQL"
>Table 9-9</A
>.
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> also provides versions of these functions
that use the regular function invocation syntax
(see <A
HREF="functions-binarystring.html#FUNCTIONS-BINARYSTRING-OTHER"
>Table 9-10</A
>).
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> The sample results shown on this page assume that the server parameter
<A
HREF="runtime-config-client.html#GUC-BYTEA-OUTPUT"
><TT
CLASS="VARNAME"
>bytea_output</TT
></A
> is set
to <TT
CLASS="LITERAL"
>escape</TT
> (the traditional PostgreSQL format).
</P
></BLOCKQUOTE
></DIV
><DIV
CLASS="TABLE"
><A
NAME="FUNCTIONS-BINARYSTRING-SQL"
></A
><P
><B
>Table 9-9. <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> Binary String Functions and Operators</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><COL><THEAD
><TR
><TH
>Function</TH
><TH
>Return Type</TH
><TH
>Description</TH
><TH
>Example</TH
><TH
>Result</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="LITERAL"
><TT
CLASS="PARAMETER"
>string</TT
> <TT
CLASS="LITERAL"
>||</TT
>
<TT
CLASS="PARAMETER"
>string</TT
></TT
></TD
><TD
> <TT
CLASS="TYPE"
>bytea</TT
> </TD
><TD
> String concatenation
</TD
><TD
><TT
CLASS="LITERAL"
>E'\\\\Post'::bytea || E'\\047gres\\000'::bytea</TT
></TD
><TD
><TT
CLASS="LITERAL"
>\\Post'gres\000</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>octet_length(<TT
CLASS="PARAMETER"
>string</TT
>)</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>int</TT
></TD
><TD
>Number of bytes in binary string</TD
><TD
><TT
CLASS="LITERAL"
>octet_length(E'jo\\000se'::bytea)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>5</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>overlay(<TT
CLASS="PARAMETER"
>string</TT
> placing <TT
CLASS="PARAMETER"
>string</TT
> from <TT
CLASS="TYPE"
>int</TT
> [<SPAN
CLASS="OPTIONAL"
>for <TT
CLASS="TYPE"
>int</TT
></SPAN
>])</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>bytea</TT
></TD
><TD
> Replace substring
</TD
><TD
><TT
CLASS="LITERAL"
>overlay(E'Th\\000omas'::bytea placing E'\\002\\003'::bytea from 2 for 3)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>T\\002\\003mas</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>position(<TT
CLASS="PARAMETER"
>substring</TT
> in <TT
CLASS="PARAMETER"
>string</TT
>)</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>int</TT
></TD
><TD
>Location of specified substring</TD
><TD
><TT
CLASS="LITERAL"
>position(E'\\000om'::bytea in E'Th\\000omas'::bytea)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>3</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>substring(<TT
CLASS="PARAMETER"
>string</TT
> [<SPAN
CLASS="OPTIONAL"
>from <TT
CLASS="TYPE"
>int</TT
></SPAN
>] [<SPAN
CLASS="OPTIONAL"
>for <TT
CLASS="TYPE"
>int</TT
></SPAN
>])</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>bytea</TT
></TD
><TD
> Extract substring
</TD
><TD
><TT
CLASS="LITERAL"
>substring(E'Th\\000omas'::bytea from 2 for 3)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>h\000o</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>trim([<SPAN
CLASS="OPTIONAL"
>both</SPAN
>]
<TT
CLASS="PARAMETER"
>bytes</TT
> from
<TT
CLASS="PARAMETER"
>string</TT
>)</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>bytea</TT
></TD
><TD
> Remove the longest string containing only bytes appearing in
<TT
CLASS="PARAMETER"
>bytes</TT
> from the start
and end of <TT
CLASS="PARAMETER"
>string</TT
>
</TD
><TD
><TT
CLASS="LITERAL"
>trim(E'\\000\\001'::bytea from E'\\000Tom\\001'::bytea)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>Tom</TT
></TD
></TR
></TBODY
></TABLE
></DIV
><P
> Additional binary string manipulation functions are available and
are listed in <A
HREF="functions-binarystring.html#FUNCTIONS-BINARYSTRING-OTHER"
>Table 9-10</A
>. Some
of them are used internally to implement the
<ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>-standard string functions listed in <A
HREF="functions-binarystring.html#FUNCTIONS-BINARYSTRING-SQL"
>Table 9-9</A
>.
</P
><DIV
CLASS="TABLE"
><A
NAME="FUNCTIONS-BINARYSTRING-OTHER"
></A
><P
><B
>Table 9-10. Other Binary String Functions</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><COL><THEAD
><TR
><TH
>Function</TH
><TH
>Return Type</TH
><TH
>Description</TH
><TH
>Example</TH
><TH
>Result</TH
></TR
></THEAD
><TBODY
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>btrim(<TT
CLASS="PARAMETER"
>string</TT
>
<TT
CLASS="TYPE"
>bytea</TT
>, <TT
CLASS="PARAMETER"
>bytes</TT
> <TT
CLASS="TYPE"
>bytea</TT
>)</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>bytea</TT
></TD
><TD
> Remove the longest string containing only bytes appearing in
<TT
CLASS="PARAMETER"
>bytes</TT
> from the start and end of
<TT
CLASS="PARAMETER"
>string</TT
>
</TD
><TD
><TT
CLASS="LITERAL"
>btrim(E'\\000trim\\001'::bytea, E'\\000\\001'::bytea)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>trim</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>decode(<TT
CLASS="PARAMETER"
>string</TT
> <TT
CLASS="TYPE"
>text</TT
>,
<TT
CLASS="PARAMETER"
>format</TT
> <TT
CLASS="TYPE"
>text</TT
>)</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>bytea</TT
></TD
><TD
> Decode binary data from textual representation in <TT
CLASS="PARAMETER"
>string</TT
>.
Options for <TT
CLASS="PARAMETER"
>format</TT
> are same as in <CODE
CLASS="FUNCTION"
>encode</CODE
>.
</TD
><TD
><TT
CLASS="LITERAL"
>decode(E'123\\000456', 'escape')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>123\000456</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>encode(<TT
CLASS="PARAMETER"
>data</TT
> <TT
CLASS="TYPE"
>bytea</TT
>,
<TT
CLASS="PARAMETER"
>format</TT
> <TT
CLASS="TYPE"
>text</TT
>)</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>text</TT
></TD
><TD
> Encode binary data into a textual representation. Supported
formats are: <TT
CLASS="LITERAL"
>base64</TT
>, <TT
CLASS="LITERAL"
>hex</TT
>, <TT
CLASS="LITERAL"
>escape</TT
>.
<TT
CLASS="LITERAL"
>escape</TT
> converts zero bytes and high-bit-set bytes to
octal sequences (<TT
CLASS="LITERAL"
>\</TT
><TT
CLASS="REPLACEABLE"
><I
>nnn</I
></TT
>) and
doubles backslashes.
</TD
><TD
><TT
CLASS="LITERAL"
>encode(E'123\\000456'::bytea, 'escape')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>123\000456</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>get_bit(<TT
CLASS="PARAMETER"
>string</TT
>, <TT
CLASS="PARAMETER"
>offset</TT
>)</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>int</TT
></TD
><TD
> Extract bit from string
</TD
><TD
><TT
CLASS="LITERAL"
>get_bit(E'Th\\000omas'::bytea, 45)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>1</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>get_byte(<TT
CLASS="PARAMETER"
>string</TT
>, <TT
CLASS="PARAMETER"
>offset</TT
>)</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>int</TT
></TD
><TD
> Extract byte from string
</TD
><TD
><TT
CLASS="LITERAL"
>get_byte(E'Th\\000omas'::bytea, 4)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>109</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>length(<TT
CLASS="PARAMETER"
>string</TT
>)</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>int</TT
></TD
><TD
> Length of binary string
</TD
><TD
><TT
CLASS="LITERAL"
>length(E'jo\\000se'::bytea)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>5</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>md5(<TT
CLASS="PARAMETER"
>string</TT
>)</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>text</TT
></TD
><TD
> Calculates the MD5 hash of <TT
CLASS="PARAMETER"
>string</TT
>,
returning the result in hexadecimal
</TD
><TD
><TT
CLASS="LITERAL"
>md5(E'Th\\000omas'::bytea)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>8ab2d3c9689aaf18 b4958c334c82d8b1</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>set_bit(<TT
CLASS="PARAMETER"
>string</TT
>,
<TT
CLASS="PARAMETER"
>offset</TT
>, <TT
CLASS="PARAMETER"
>newvalue</TT
>)</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>bytea</TT
></TD
><TD
> Set bit in string
</TD
><TD
><TT
CLASS="LITERAL"
>set_bit(E'Th\\000omas'::bytea, 45, 0)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>Th\000omAs</TT
></TD
></TR
><TR
><TD
>
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>set_byte(<TT
CLASS="PARAMETER"
>string</TT
>,
<TT
CLASS="PARAMETER"
>offset</TT
>, <TT
CLASS="PARAMETER"
>newvalue</TT
>)</CODE
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>bytea</TT
></TD
><TD
> Set byte in string
</TD
><TD
><TT
CLASS="LITERAL"
>set_byte(E'Th\\000omas'::bytea, 4, 64)</TT
></TD
><TD
><TT
CLASS="LITERAL"
>Th\000o@as</TT
></TD
></TR
></TBODY
></TABLE
></DIV
><P
> <CODE
CLASS="FUNCTION"
>get_byte</CODE
> and <CODE
CLASS="FUNCTION"
>set_byte</CODE
> number the first byte
of a binary string as byte 0.
<CODE
CLASS="FUNCTION"
>get_bit</CODE
> and <CODE
CLASS="FUNCTION"
>set_bit</CODE
> number bits from the
right within each byte; for example bit 0 is the least significant bit of
the first byte, and bit 15 is the most significant bit of the second byte.
</P
><P
> See also the aggregate function <CODE
CLASS="FUNCTION"
>string_agg</CODE
> in
<A
HREF="functions-aggregate.html"
>Section 9.20</A
>.
</P
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