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Counting common elements in MySQL?
To count common elements, use COUNT() and GROUP BY. Let us first create a table −
mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, Number int ); Query OK, 0 rows affected (0.20 sec)
Insert some records in the table using insert command −
mysql> insert into DemoTable(Number) values(10); Query OK, 1 row affected (0.06 sec) mysql> insert into DemoTable(Number) values(20); Query OK, 1 row affected (0.04 sec) mysql> insert into DemoTable(Number) values(20); Query OK, 1 row affected (0.04 sec) mysql> insert into DemoTable(Number) values(30); Query OK, 1 row affected (0.04 sec) mysql> insert into DemoTable(Number) values(10); Query OK, 1 row affected (0.05 sec) mysql> insert into DemoTable(Number) values(10); Query OK, 1 row affected (0.04 sec)
Display all records from the table using select statement −
mysql> select *from DemoTable;
This will produce the following output −
+----+--------+ | Id | Number | +----+--------+ | 1 | 10 | | 2 | 20 | | 3 | 20 | | 4 | 30 | | 5 | 10 | | 6 | 10 | +----+--------+ 6 rows in set (0.00 sec)
Following is the query to count common elements −
mysql> select Number,count(Number) as CommonElement from DemoTable group by Number;
This will produce the following output −
+--------+---------------+ | Number | CommonElement | +--------+---------------+ | 10 | 3 | | 20 | 2 | | 30 | 1 | +--------+---------------+ 3 rows in set (0.00 sec)
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