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 with a special syntax where certain key words rather than commas are used to separate the arguments. Details are in Table 9.8, “SQL Binary String Functions and Operators”. Some functions are also implemented using the regular syntax for function invocation. (See Table 9.9, “Other Binary String Functions”.)

Table 9.8. SQL Binary String Functions and Operators

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

position(substring in string)

int

Location of specified substring

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

3

substring(string [from int] [for int])

bytea

Extract substring

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

h\000o

trim([both] bytes from string)

bytea

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

trim('\\000'::bytea from '\\000Tom\\000'::bytea)

Tom

get_byte(string, offset)

int

Extract byte from string

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

109

set_byte(string, offset, newvalue)

bytea

Set byte in string

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

Th\[email protected]

get_bit(string, offset)

int

Extract bit from string

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

1

set_bit(string, offset, newvalue)

bytea

Set bit in string

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

Th\000omAs

Additional binary string manipulation functions are available and are listed in Table 9.9, “Other Binary String Functions”. Some of them are used internally to implement the SQL-standard string functions listed in Table 9.8, “SQL Binary String Functions and Operators”.

Table 9.9. Other Binary String Functions

Function

Return Type

Description

Example

Result

btrim(string bytea, bytes bytea)

bytea

Remove the longest string consisting only of bytes in bytes from the start and end of string

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

trim

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

decode(string text, type text)

bytea

Decode binary string from string previously encoded with encode. Parameter type is same as in encode.

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

123\000456

encode(string bytea, type text)

text

Encode binary string to ASCII-only representation. Supported types are: base64, hex, escape.

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

123\000456