8.10. 位元字串型別
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Bit strings are strings of 1's and 0's. They can be used to store or visualize bit masks. There are two SQL bit types: bit(
n
) and bit varying(
n
), where n
is a positive integer.
bit
type data must match the length n
exactly; it is an error to attempt to store shorter or longer bit strings. bit varying
data is of variable length up to the maximum length n
; longer strings will be rejected. Writing bit
without a length is equivalent to bit(1)
, while bit varying
without a length specification means unlimited length.
If one explicitly casts a bit-string value to bit(
n
), it will be truncated or zero-padded on the right to be exactly n
bits, without raising an error. Similarly, if one explicitly casts a bit-string value to bit varying(
n
), it will be truncated on the right if it is more than n
bits.
Refer to for information about the syntax of bit string constants. Bit-logical operators and string manipulation functions are available; see .
Example 8.3. Using the Bit String Types
A bit string value requires 1 byte for each group of 8 bits, plus 5 or 8 bytes overhead depending on the length of the string (but long values may be compressed or moved out-of-line, as explained in for character strings).