9.5. Binary
String Functions and Operators
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 9.11. PostgreSQL
also provides versions of these functions that use the regular
function invocation syntax (see Table 9.12).
Note
The sample results shown on this page assume that the server
parameter bytea_output is set to escape (the traditional PostgreSQL
format).
Table 9.11. 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 |
octet_length(string) |
int |
Number of bytes in binary string |
octet_length(E'jo\\000se'::bytea) |
5 |
overlay(string placing string from int [for
int]) |
bytea |
Replace substring |
overlay(E'Th\\000omas'::bytea
placing E'\\002\\003'::bytea from 2 for 3) |
T\\002\\003mas |
position(substring in string) |
int |
Location of specified substring |
position(E'\\000om'::bytea in
E'Th\\000omas'::bytea) |
3 |
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 bytes
appearing in bytes from the start and
end of string |
trim(E'\\000\\001'::bytea
from E'\\000Tom\\001'::bytea) |
Tom |
Additional binary string manipulation functions are available
and are listed in Table 9.12.
Some of them are used internally to implement the SQL-standard string functions listed in
Table 9.11.
Table 9.12. Other Binary
String Functions
| Function |
Return Type |
Description |
Example |
Result |
btrim(string bytea, bytes bytea) |
bytea |
Remove the longest string containing only bytes
appearing in bytes from the start and
end of string |
btrim(E'\\000trim\\001'::bytea,
E'\\000\\001'::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 |
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 |
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 |
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 |
get_byte and set_byte number the first byte of a binary
string as byte 0. get_bit and
set_bit number bits from the right
within each byte; for example bit 0 is the least significant bit
of the first byte, and bit 15 is the most significant bit of the
second byte.
See also the aggregate function string_agg in Section 9.20 and the
large object functions in Section 34.4.
