PostgreSQL 8.2.6 Documentation
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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 . Some functions are also implemented using the regular syntax for function invocation. (See Table 9-9 .)

Table 9-8. SQL Binary 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
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
octet_length ( string ) int Number of bytes in binary string octet_length( E'jo\\000se'::bytea) 5
position ( substring in string ) int Location of specified substring position(E'\\000om'::bytea in E'Th\\000omas'::bytea) 3
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
substring ( string [ from int ] [ for int ]) bytea Extract substring substring(E'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(E'\\000'::bytea from E'\\000Tom\\000'::bytea) Tom

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

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(E'\\000trim\\000'::bytea, E'\\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(E'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(E'123\\000456'::bytea, 'escape') 123\000456
length ( string ) int Length of binary string length(E'jo\\000se'::bytea) 5
md5 ( string ) text Calculates the MD5 hash of string , returning the result in hexadecimal md5(E'Th\\000omas'::bytea) 8ab2d3c9689aaf18 b4958c334c82d8b1
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