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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
9-8. PostgreSQL also
provides versions of these functions that use the regular
function invocation syntax (see Table
9-9).
Table 9-8. SQL
Binary String Functions and Operators
| Function |
Return Type |
Description |
Example |
Result |
| string
|| string |
bytea |
String concatenation |
E'\\\\Post'::bytea ||
E'\047円gres\000円'::bytea |
\\Post'gres000円 |
get_bit(string, offset) |
int |
Extract bit from string |
get_bit(E'Th\000円omas'::bytea,
45) |
1 |
get_byte(string, offset) |
int |
Extract byte from string |
get_byte(E'Th\000円omas'::bytea,
4) |
109 |
octet_length(string) |
int |
Number of bytes in binary string |
octet_length(E'jo\000円se'::bytea) |
5 |
position(substring in string) |
int |
Location of specified substring |
position(E'\000円om'::bytea in
E'Th\000円omas'::bytea) |
3 |
set_bit(string, offset, newvalue) |
bytea |
Set bit in string |
set_bit(E'Th\000円omas'::bytea,
45, 0) |
Th000円omAs |
set_byte(string, offset, newvalue) |
bytea |
Set byte in string |
set_byte(E'Th\000円omas'::bytea,
4, 64) |
Th000円o@as |
substring(string [from
int] [for int]) |
bytea |
Extract substring |
substring(E'Th\000円omas'::bytea
from 2 for 3) |
h000円o |
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円'::bytea from
E'\000円Tom\000円'::bytea) |
Tom |
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(E'\000円trim\000円'::bytea,
E'\000円'::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円',
'escape') |
123000456円 |
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円'::bytea,
'escape') |
123000456円 |
length(string) |
int |
Length of binary string |
length(E'jo\000円se'::bytea) |
5 |
md5(string) |
text |
Calculates the MD5 hash of string, returning the result in
hexadecimal |
md5(E'Th\000円omas'::bytea) |
8ab2d3c9689aaf18
b4958c334c82d8b1 |
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