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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 9-9. PostgreSQL also provides versions of these functions that use the regular function invocation syntax (see Table 9-10).

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

Table 9-9. 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
octet_length(string) int Number of bytes in binary string octet_length(E'jo\\000se'::bytea) 5
overlay(string placing string from int [for int]) bytea Replace substring overlay(E'Th\\000omas'::bytea placing E'\\002\\003'::bytea from 2 for 3) T\\002\\003mas
position(substring in string) int Location of specified substring position(E'\\000om'::bytea in E'Th\\000omas'::bytea) 3
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 9-10. Some of them are used internally to implement the SQL-standard string functions listed in Table 9-9.

Table 9-10. 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, format text) bytea Decode binary data from textual representation in string. Options for format are same as in encode. decode(E'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(E'123\\000456'::bytea, 'escape') 123\000456
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
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
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

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.