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9.5. Binary String Functions and Operators
This section describes functions and operators for examining and manipulating values of typebytea.
SQL defines some string functions that use key words, rather than commas, to separate arguments. Details are inTable 9-9.PostgreSQL also provides versions of these functions that use the regular function invocation syntax (seeTable 9-10).
Note: The sample results shown on this page assume that the server parameterbytea_output is set toescape (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 placingstring fromint [forint]) | bytea | Replace substring | overlay(E'Th\\000omas'::bytea placing E'\\002\\003'::bytea from 2 for 3) | T\\002\\003mas |
position(substring instring) | int | Location of specified substring | position(E'\\000om'::bytea in E'Th\\000omas'::bytea) | 3 |
substring(string [fromint] [forint]) | bytea | Extract substring | substring(E'Th\\000omas'::bytea from 2 for 3) | h\000o |
trim([both]bytes fromstring) | bytea | Remove the longest string containing only the bytes inbytes from the start and end ofstring | trim(E'\\000'::bytea from E'\\000Tom\\000'::bytea) | Tom |
Additional binary string manipulation functions are available and are listed inTable 9-10. Some of them are used internally to implement theSQL-standard string functions listed inTable 9-9.
Table 9-10. Other Binary String Functions
| Function | Return Type | Description | Example | Result |
|---|---|---|---|---|
btrim(stringbytea,bytesbytea) | bytea | Remove the longest string consisting only of bytes inbytes from the start and end ofstring | btrim(E'\\000trim\\000'::bytea, E'\\000'::bytea) | trim |
decode(stringtext,formattext) | bytea | Decode binary data from textual representation instring. Options forformat are same as inencode. | decode(E'123\\000456', 'escape') | 123\000456 |
encode(databytea,formattext) | 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 ofstring, 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 andset_byte number the first byte of a binary string as byte 0.get_bit andset_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.
See also the aggregate functionstring_agg inSection 9.20 and the large object functions inSection 32.4.