Bit String Types

Updated at: Mar 13, 2020 GMT+08:00

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

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), it will be truncated on the right if it is more than n bits.

-- Create a table:
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');

-- Specify the type length. An error is reported if an inserted string exceeds this length.
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

-- Specify the type length. Data is converted if it exceeds this length.
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)

-- Delete the tables:
DROP TABLE bit_type_t1;

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