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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'\\047gres\\000'::bytea |
\\Post'gres\000 |
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 |
octet_length(string) |
int |
Number of bytes in binary string |
octet_length(E'jo\\000se'::bytea) |
5 |
position(substring in string) |
int |
Location of specified substring |
position(E'\\000om'::bytea in
E'Th\\000omas'::bytea) |
3 |
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 |
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
9-9. 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'\\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 |
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 |