Bit String Types

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.

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:

1. Create a sample table bit_type_t1.

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

2. Insert data:

   1	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.

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   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

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

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

4. View data:

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