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 9.12. PostgreSQL also provides versions of these functions that use the regular function invocation syntax (see Table 9.13).

Note

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

Table 9.12. 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`+ [`[.optional]#`+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`+ [`[.optional]#`+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 9.13. Some of them are used internally to implement the SQL-standard string functions listed in Table 9.12.

Table 9.13. 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)`	`8ab2d3c9689aaf18b4958c334c82d8b1`
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`
`sha224(bytea)`	`bytea`	SHA-224 hash	`sha224('abc')`	`\x23097d223405d8228642a477bda255b32aadbce4bda0b3f7e36c9da7`
`sha256(bytea)`	`bytea`	SHA-256 hash	`sha256('abc')`	`\xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad`
`sha384(bytea)`	`bytea`	SHA-384 hash	`sha384('abc')`	`\xcb00753f45a35e8bb5a03d699ac65007272c32ab0eded1631a8b605a43ff5bed8086072ba1e7cc2358baeca134c825a7`
`sha512(bytea)`	`bytea`	SHA-512 hash	`sha512('abc')`	`\xddaf35a193617abacc417349ae20413112e6fa4e89a97ea20a9eeee64b55d39a2192992a274fc1a836ba3c23a3feebbd454d4423643ce80e2a9ac94fa54ca49f`

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)

8ab2d3c9689aaf18b4958c334c82d8b1

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

sha224(bytea)

bytea

SHA-224 hash

sha224('abc')

\x23097d223405d8228642a477bda255b32aadbce4bda0b3f7e36c9da7

sha256(bytea)

bytea

SHA-256 hash

sha256('abc')

\xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad

sha384(bytea)

bytea

SHA-384 hash

sha384('abc')

\xcb00753f45a35e8bb5a03d699ac65007272c32ab0eded1631a8b605a43ff5bed8086072ba1e7cc2358baeca134c825a7

sha512(bytea)

bytea

SHA-512 hash

sha512('abc')

\xddaf35a193617abacc417349ae20413112e6fa4e89a97ea20a9eeee64b55d39a2192992a274fc1a836ba3c23a3feebbd454d4423643ce80e2a9ac94fa54ca49f

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.

Note that for historic reasons, the function md5 returns a hex-encoded value of type text whereas the SHA-2 functions return type bytea. Use the functions encode and decode to convert between the two, for example encode(sha256('abc'), 'hex') to get a hex-encoded text representation.

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

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