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) | integer | Number of bytes in binary string | octet_length( 'jo\\000se'::bytea) | 5 |
position(substring in string) | integer | Location of specified substring | position('\\000om'::bytea in 'Th\\000omas'::bytea) | 3 |
substring(string [from integer] [for integer]) | 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) | integer | 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) | integer | 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) | integer | Length of binary string | length('jo\\000se'::bytea) | 5 |
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 |
