Documentação do PostgreSQL 8.2.0
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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 Tabela 9-8. Some functions are also implemented using the regular syntax for function invocation. (See Tabela 9-9.)

Tabela 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
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
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
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
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

Additional binary string manipulation functions are available and are listed in Tabela 9-9. Some of them are used internally to implement the SQL-standard string functions listed in Tabela 9-8.

Tabela 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
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
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

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String Functions and Operators	Acima	Bit String Functions and Operators