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Chapter 6.
Functions and Operators |
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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 ||
'\047円greSQL\000円'::bytea |
\\Post'greSQL000円 |
octet_length(string) |
integer |
Number of bytes in binary string |
octet_length('jo\000円se'::bytea) |
5 |
position(substring in string) |
integer |
Location of specified substring |
position('\000円om'::bytea in
'Th\000円omas'::bytea) |
3 |
substring(string [from
integer] [for integer]) |
bytea |
Extract substring |
substring('Th\000円omas'::bytea
from 2 for 3) |
h000円o |
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円'::bytea from
'\000円Tom\000円'::bytea) |
Tom |
get_byte(string, offset) |
integer |
Extract byte from string. |
get_byte('Th\000円omas'::bytea,
4) |
109 |
set_byte(string, offset, newvalue) |
bytea |
Set byte in string. |
set_byte('Th\000円omas'::bytea, 4,
64) |
Th000円o@as |
get_bit(string, offset) |
integer |
Extract bit from string. |
get_bit('Th\000円omas'::bytea,
45) |
1 |
set_bit(string, offset, newvalue) |
bytea |
Set bit in string. |
set_bit('Th\000円omas'::bytea, 45,
0) |
Th000円omAs |
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('\000円trim\000円'::bytea,'\000円'::bytea) |
trim |
length(string) |
integer |
Length of binary string |
length('jo\000円se'::bytea) |
5 |
encode(string bytea,
type text) |
text |
Encode binary string to ASCII-only representation. Supported
types are: base64, hex, escape. |
encode('123\000456円'::bytea,
'escape') |
123000456円 |
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円',
'escape') |
123000456円 |