| PostgreSQL 9.0.23 Documentation | ||||
|---|---|---|---|---|
| Prev | Up | Chapter 9. Functions and Operators | Next | |
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.