Bit String Functions and Operators
| PostgreSQL 9.2.20 Documentation | ||||
|---|---|---|---|---|
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This section describes functions and operators for examining and manipulating bit strings, that is values of the types bit and bit varying . Aside from the usual comparison operators, the operators shown in Table 9-11 can be used. Bit string operands of & , | , and # must be of equal length. When bit shifting, the original length of the string is preserved, as shown in the examples.
Table 9-11. Bit String Operators
| Operator | Description | Example | Result |
|---|---|---|---|
| || | concatenation | B'10001' || B'011' | 10001011 |
| & | bitwise AND | B'10001' & B'01101' | 00001 |
| | | bitwise OR | B'10001' | B'01101' | 11101 |
| # | bitwise XOR | B'10001' # B'01101' | 11100 |
| ~ | bitwise NOT | ~ B'10001' | 01110 |
| << | bitwise shift left | B'10001' << 3 | 01000 |
| >> | bitwise shift right | B'10001' >> 2 | 00100 |
The following
SQL
-standard functions work on bit
strings as well as character strings:
length
,
bit_length
,
octet_length
,
position
,
substring
,
overlay
.
The following functions work on bit strings as well as binary
strings:
get_bit
,
set_bit
.
When working with a bit string, these functions number the first
(leftmost) bit of the string as bit 0.
In addition, it is possible to cast integral values to and from type bit . Some examples:
44::bit(10) 0000101100 44::bit(3) 100 cast(-44 as bit(12)) 111111010100 '1110'::bit(4)::integer 14
Note that casting to just "bit" means casting to bit(1) , and so will deliver only the least significant bit of the integer.
Note: Prior to PostgreSQL 8.0, casting an integer to bit(n) would copy the leftmost n bits of the integer, whereas now it copies the rightmost n bits. Also, casting an integer to a bit string width wider than the integer itself will sign-extend on the left.