Binary String Functions and Operators
This section describes functions and operators for examining and
manipulating binary string values. Strings in this context mean
values of the 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 6-9.
Some functions are also implemented using the regular syntax for
function invocation.
(See Table 6-10.)
Table 6-9. SQL Binary String Functions and Operators
| Function | Return Type | Description | Example | Result |
|---|
| string ||
string | bytea | String concatenation
| '\\\\Post'::bytea || '\\047greSQL\\000'::bytea | \\Post'greSQL\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]
characters from
string)
| bytea | Remove the longest string containing only the
characters from the
beginning/end/both ends of the 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 6-10. Some
of them are used internally to implement the
SQL-standard string functions listed in Table 6-9.
Table 6-10. Other Binary String Functions
| Function | Return Type | Description | Example | Result |
|---|
btrim(string
bytea trim bytea) | bytea | Remove (trim) the longest string consisting only of characters
in trim 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 |
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 |
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 |
