This section describes functions and operators for examining and manipulating values of typebytea.
SQLdefines some string functions that use key words, rather than commas, to separate arguments. Details are inTable 9.11.PostgreSQLalso provides versions of these functions that use the regular function invocation syntax (seeTable 9.12).
The sample results shown on this page assume that the server parameterbytea_outputis set toescape(the traditional PostgreSQL format).
Table 9.11. SQLBinary String Functions and Operators
Function
Return Type
Description
Example
Result
string`
_string`_
bytea
String concatenation
`E'\\Post'::bytea
E'\047gres\000'::bytea`
\\Post'gres\000
octet_length(string)
int
Number of bytes in binary string
octet_length(E'jo\\000se'::bytea)
5
overlay(string_placingstring_fromint[forint])
bytea
Replace substring
overlay(E'Th\\000omas'::bytea placing E'\\002\\003'::bytea from 2 for 3)
T\\002\\003mas
position(substring_instring_)
int
Location of specified substring
position(E'\\000om'::bytea in E'Th\\000omas'::bytea)
3
substring(string[fromint] [forint])
bytea
Extract substring
substring(E'Th\\000omas'::bytea from 2 for 3)
h\000o
trim([both]bytes_fromstring_)
bytea
Remove the longest string containing only bytes appearing inbytes_from the start and end ofstring_
trim(E'\\000\\001'::bytea from E'\\000Tom\\001'::bytea)
Tom
Additional binary string manipulation functions are available and are listed inTable 9.12. Some of them are used internally to implement theSQL-standard string functions listed inTable 9.11.
Table 9.12. Other Binary String Functions
Function
Return Type
Description
Example
Result
btrim(stringbytea,bytesbytea)
bytea
Remove the longest string containing only bytes appearing inbytes_from the start and end ofstring_
btrim(E'\\000trim\\001'::bytea, E'\\000\\001'::bytea)
trim
decode(stringtext,formattext)
bytea
Decode binary data from textual representation instring. Options for_format_are same as inencode.
decode(E'123\\000456', 'escape')
123\000456
encode(databytea,formattext)
text
Encode binary data into a textual representation. Supported formats are:base64,hex,escape.escapeconverts zero bytes and high-bit-set bytes to octal sequences (\nnn) and doubles backslashes.
encode(E'123\\000456'::bytea, 'escape')
123\000456
get_bit(string,offset)
int
Extract bit from string
get_bit(E'Th\\000omas'::bytea, 45)
1
get_byte(string,offset)
int
Extract byte from string
get_byte(E'Th\\000omas'::bytea, 4)
109
length(string)
int
Length of binary string
length(E'jo\\000se'::bytea)
5
md5(string)
text
Calculates the MD5 hash ofstring, returning the result in hexadecimal
md5(E'Th\\000omas'::bytea)
8ab2d3c9689aaf18 b4958c334c82d8b1
set_bit(string,offset,newvalue)
bytea
Set bit in string
set_bit(E'Th\\000omas'::bytea, 45, 0)
Th\000omAs
set_byte(string,offset,newvalue)
bytea
Set byte in string
set_byte(E'Th\\000omas'::bytea, 4, 64)
Th\000o@as
get_byteandset_bytenumber the first byte of a binary string as byte 0.get_bitandset_bitnumber 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.
See also the aggregate functionstring_agginSection 9.20and the large object functions inSection 34.4.