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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 '\\\\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\000o@as
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. 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('\\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

  Published courtesy of The PostgreSQL Global Development Group Design by Interspire