Null check
mysql>
mysql> CREATE TABLE IF NOT EXISTS steam_irons
-> (
-> id INT AUTO_INCREMENT PRIMARY KEY,
-> make VARCHAR(25) NOT NULL,
-> model VARCHAR(25) NOT NULL,
-> color VARCHAR(25)
-> );
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql> # insert 5 records into the "steam_irons" table
mysql> INSERT INTO steam_irons (make, model, color) VALUES ("Philips", "GC3020", "Lilac");
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO steam_irons (make, model) VALUES ("Morphy Richards", "40608");
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO steam_irons (make, model) VALUES ("Tefal", "1819 Avantis");
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO steam_irons (make, model) VALUES ("Rowenta", "DM529");
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO steam_irons (make, model, color) VALUES ("Bosch", "TDA8360", "Blue");
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> # show the table format
mysql> EXPLAIN steam_irons;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| make | varchar(25) | NO | | NULL | |
| model | varchar(25) | NO | | NULL | |
| color | varchar(25) | YES | | NULL | |
+-------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
mysql>
mysql> # show all data in the "steam_irons" table
mysql> SELECT * FROM steam_irons;
+----+-----------------+--------------+-------+
| id | make | model | color |
+----+-----------------+--------------+-------+
| 1 | Philips | GC3020 | Lilac |
| 2 | Morphy Richards | 40608 | NULL |
| 3 | Tefal | 1819 Avantis | NULL |
| 4 | Rowenta | DM529 | NULL |
| 5 | Bosch | TDA8360 | Blue |
+----+-----------------+--------------+-------+
5 rows in set (0.00 sec)
mysql>
mysql> # show all records where there is no specified color
mysql> SELECT * FROM steam_irons WHERE color IS NULL;
+----+-----------------+--------------+-------+
| id | make | model | color |
+----+-----------------+--------------+-------+
| 2 | Morphy Richards | 40608 | NULL |
| 3 | Tefal | 1819 Avantis | NULL |
| 4 | Rowenta | DM529 | NULL |
+----+-----------------+--------------+-------+
3 rows in set (0.00 sec)
mysql>
mysql> # delete this sample table
mysql> DROP TABLE IF EXISTS steam_irons;
Query OK, 0 rows affected (0.00 sec)
mysql>
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