PostgreSQL

9.5. Binary String Functions and Operators
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9.5. Binary String Functions and Operators

This section describes functions and operators for examining and manipulating values of type bytea.

SQL defines some string functions that use key words, rather than commas, to separate arguments. Details are in Table 9.11. PostgreSQL also provides versions of these functions that use the regular function invocation syntax (see Table 9.12).

Note

The sample results shown on this page assume that the server parameter bytea_output is set to escape (the traditional PostgreSQL format).

Table 9.11. SQL Binary String Functions and Operators

Function Return Type Description Example Result

Function	Return Type	Description	Example	Result
`string+ ``		`` `_`+string`_	`bytea`	String concatenation
`+'\\Post'::bytea		'\047gres\000'::bytea+`	`\\Post'gres\000`	+octet_length(+`+string++)+`
`int`	Number of bytes in binary string	`octet_length('jo\000se'::bytea)`	`5`	+overlay(+`+string++ placing `_`+string`_`+ from ``+int`+` +for +int])`
`bytea`	Replace substring	`overlay('Th\000omas'::bytea placing '\002\003'::bytea from 2 for 3)`	`T\\002\\003mas`	+position(+`+substring++ in `_`+string`_`)`
`int`	Location of specified substring	`position('\000om'::bytea in 'Th\000omas'::bytea)`	`3`	+substring(+`+string++ +for +`int`])`
`bytea`	Extract substring	`substring('Th\000omas'::bytea from 2 for 3)`	`h\000o`	`trim([both`+] +`+bytes++ from `_`+string`_`)`

`string+ ``

`` `_`+string`_

bytea

String concatenation

`+'\\Post'::bytea

'\047gres\000'::bytea+`

\\Post'gres\000

+octet_length(+`+string++)+`

int

Number of bytes in binary string

octet_length('jo\000se'::bytea)

5

+overlay(+`+string++ placing `_`+string_+ from ``+int+ +for +int])`

bytea

Replace substring

overlay('Th\000omas'::bytea placing '\002\003'::bytea from 2 for 3)

T\\002\\003mas

+position(+`+substring++ in `_`+string_)`

int

Location of specified substring

position('\000om'::bytea in 'Th\000omas'::bytea)

3

+substring(+`+string++ +for +`int])

bytea

Extract substring

substring('Th\000omas'::bytea from 2 for 3)

h\000o

trim([both+] +`+bytes++ from `_`+string_)`

Additional binary string manipulation functions are available and are listed in Table 9.12. Some of them are used internally to implement the SQL-standard string functions listed in Table 9.11.

Table 9.12. Other Binary String Functions

Function Return Type Description Example Result

Function	Return Type	Description	Example	Result
+btrim(+`+string++ ``+bytea+, ++bytes++ ``+bytea)`	`bytea`	Remove the longest string containing only bytes appearing in `bytes `from the start and end of` string`	`btrim('\000trim\001'::bytea, '\000\001'::bytea)`	`trim`
+decode(+`+string++ ``+text+, ++format++ ``+text)`	`bytea`	Decode binary data from textual representation in `string`. Options for` format are same as in `encode.	`decode('123\000456', 'escape')`	`123\000456`
+encode(+`+data++ ``+bytea+, ++format++ ``+text)`	`text`	Encode binary data into a textual representation. Supported formats are: `base64`, `hex`, `escape`. `escape` converts zero bytes and high-bit-set bytes to octal sequences (+\+`+nnn+`) and doubles backslashes.	`encode('123\000456'::bytea, 'escape')`	`123\000456`
+get_bit(+`+string++, `_`+offset`_`)`	`int`	Extract bit from string	`get_bit('Th\000omas'::bytea, 45)`	`1`
+get_byte(+`+string++, `_`+offset`_`)`	`int`	Extract byte from string	`get_byte('Th\000omas'::bytea, 4)`	`109`
+length(+`+string++)+`	`int`	Length of binary string	`length('jo\000se'::bytea)`	`5`
+md5(+`+string++)+`	`text`	Calculates the MD5 hash of `string`, returning the result in hexadecimal	`md5('Th\000omas'::bytea)`	`8ab2d3c9689aaf18 b4958c334c82d8b1`
+set_bit(+`+string++, `_`+offset, +`_`+newvalue)`	`bytea`	Set bit in string	`set_bit('Th\000omas'::bytea, 45, 0)`	`Th\000omAs`
+set_byte(+`+string++, `_`+offset, +`_`+newvalue)`	`bytea`	Set byte in string	`set_byte('Th\000omas'::bytea, 4, 64)`	`Th\000o@as`

+btrim(+`+string++ ``+bytea+, ++bytes++ ``+bytea)`

bytea

Remove the longest string containing only bytes appearing in `bytes from the start and end of string`

btrim('\000trim\001'::bytea, '\000\001'::bytea)

trim

+decode(+`+string++ ``+text+, ++format++ ``+text)`

bytea

Decode binary data from textual representation in `string. Options for format are same as in `encode.

decode('123\000456', 'escape')

123\000456

+encode(+`+data++ ``+bytea+, ++format++ ``+text)`

text

Encode binary data into a textual representation. Supported formats are: base64, hex, escape. escape converts zero bytes and high-bit-set bytes to octal sequences (+\+`+nnn+`) and doubles backslashes.

encode('123\000456'::bytea, 'escape')

123\000456

+get_bit(+`+string++, `_`+offset_)`

int

Extract bit from string

get_bit('Th\000omas'::bytea, 45)

1

+get_byte(+`+string++, `_`+offset_)`

int

Extract byte from string

get_byte('Th\000omas'::bytea, 4)

109

+length(+`+string++)+`

int

Length of binary string

length('jo\000se'::bytea)

5

+md5(+`+string++)+`

text

Calculates the MD5 hash of `string`, returning the result in hexadecimal

md5('Th\000omas'::bytea)

8ab2d3c9689aaf18 b4958c334c82d8b1

+set_bit(+`+string++, `_`+offset, +`_`+newvalue)`

bytea

Set bit in string

set_bit('Th\000omas'::bytea, 45, 0)

Th\000omAs

+set_byte(+`+string++, `_`+offset, +`_`+newvalue)`

bytea

Set byte in string

set_byte('Th\000omas'::bytea, 4, 64)

Th\000o@as

get_byte and set_byte number the first byte of a binary string as byte 0. get_bit and set_bit 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.

See also the aggregate function string_agg in Section 9.20 and the large object functions in Section 34.4.

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