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9.6. Bit String Functions and Operators

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 9-10 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 9-10. 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 .

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 it 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.


 
 
  Published courtesy of The PostgreSQL Global Development Group Design by Interspire