Missing and non-missing counts can be determined for subgroups as well. : Group « Select Clause « SQL / MySQL






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  2. Select Clause
  3. Group

Missing and non-missing counts can be determined for subgroups as well.

      
mysql>
mysql>
mysql> CREATE TABLE expt
    -> (
    ->  subject VARCHAR(10),
    ->  test    VARCHAR(5),
    ->  score   INT
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql> INSERT INTO expt (subject,test,score) VALUES('Jane','A',47);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO expt (subject,test,score) VALUES('Jane','B',50);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO expt (subject,test,score) VALUES('Jane','C',NULL);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO expt (subject,test,score) VALUES('Jane','D',NULL);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO expt (subject,test,score) VALUES('Marvin','A',52);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO expt (subject,test,score) VALUES('Marvin','B',45);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO expt (subject,test,score) VALUES('Marvin','C',53);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO expt (subject,test,score) VALUES('Marvin','D',NULL);
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> SELECT * FROM expt;
+---------+------+-------+
| subject | test | score |
+---------+------+-------+
| Jane    | A    |    47 |
| Jane    | B    |    50 |
| Jane    | C    |  NULL |
| Jane    | D    |  NULL |
| Marvin  | A    |    52 |
| Marvin  | B    |    45 |
| Marvin  | C    |    53 |
| Marvin  | D    |  NULL |
+---------+------+-------+
8 rows in set (0.00 sec)

mysql>
mysql> SELECT subject,
    -> COUNT(*) AS total,
    -> COUNT(score) AS 'non-missing',
    -> COUNT(*) - COUNT(score) AS missing
    -> FROM expt GROUP BY subject;
+---------+-------+-------------+---------+
| subject | total | non-missing | missing |
+---------+-------+-------------+---------+
| Jane    |     4 |           2 |       2 |
| Marvin  |     4 |           3 |       1 |
+---------+-------+-------------+---------+
2 rows in set (0.00 sec)

mysql>
mysql> drop table expt;
Query OK, 0 rows affected (0.00 sec)








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