NULL indicates unknown data. NULL and 0 cannot be compared because they are not equivalent to each other.
When creating a table, you can specify whether NULL can be stored in a column. For details, see NOT NULL. This section describes the IS NULL and IS NOT NULL operators.
Create the customer_t1 table. The data in the table is as follows:
openGauss=# SELECT * FROM customer_t1;
c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
---------------+---------------+--------------+-------------+--------
3869 | hello | Grace | | 1000
3869 | | Grace | |
3869 | hello | | |
6985 | maps | Joes | | 2200
9976 | world | James | | 5000
4421 | Admin | Local | | 3000
(6 rows)
IS NOT NULL
In the WHERE clause, locate the column whose value is NULL.
For example, list the column whose c_customer_id is not set to a null value in the customer_t1 table.
openGauss=# SELECT * FROM customer_t1 WHERE c_customer_id IS NOT NULL;
c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
---------------+---------------+--------------+-------------+--------
3869 | hello | Grace | | 1000
3869 | hello | | |
6985 | maps | Joes | | 2200
9976 | world | James | | 5000
4421 | Admin | Local | | 3000
(5 rows)
IS NULL
In the WHERE clause, locate the column whose value is NULL.
For example, list the column whose c_customer_id is set to a null value in the customer_t1 table.
openGauss=# SELECT * FROM customer_t1 WHERE c_customer_id IS NULL;
c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
---------------+---------------+--------------+-------------+--------
3869 | | Grace | |
(1 row)
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