Bit String Types

Updated on 2024-12-19 GMT+08:00

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Bit strings are strings of 1's and 0's. They can be used to store bit masks.

GaussDB(DWS) supports two SQL bit types: bit(n) and bit varying(n), where n is a positive integer.

The bit type data must match the length n exactly. It is an error to attempt to store shorter or longer bit strings. The 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.

NOTE:

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), the bits after n places will be truncated.

The following is an example of using the bit string type:

Create a sample table bit_type_t1.

     
        CREATE TABLE bit_type_t1 
(
    BT_COL1 INTEGER,
    BT_COL2 BIT(3),
    BT_COL3 BIT VARYING(5)
) DISTRIBUTE BY REPLICATION;

Insert data:

     
        INSERT INTO bit_type_t1 VALUES(1, B'101', B'00');

An error is reported if an inserted string exceeds the length of this data type.

      
         INSERT INTO bit_type_t1 VALUES(2, B'10', B'101');
ERROR:  bit string length 2 does not match type bit(3)
CONTEXT:  referenced column: bt_col2

Data is converted if it exceeds the length of this data type.

     
        INSERT INTO bit_type_t1 VALUES(2, B'10'::bit(3), B'101');

View data:

     
        SELECT * FROM bit_type_t1;
 bt_col1 | bt_col2 | bt_col3 
---------+---------+---------
       1 | 101     | 00
       2 | 100     | 101
(2 rows)