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Can we ignore duplicate rows in COUNT?
Yes, we can ignore duplicate rows in COUNT using DISTINCT. Following is the syntax:
select count(distinct yourColumnName) from yourTableName;
In MySQL, COUNT() will display the number of rows. DISTINCT is used to ignore duplicate rows and get the count of only unique rows.
Let us first create a table:
mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, FirstName varchar(10) ); Query OK, 0 rows affected (0.47 sec)
Following is the query to insert some records in the table using insert command:
mysql> insert into DemoTable(FirstName) values('Larry');
Query OK, 1 row affected (0.18 sec)
mysql> insert into DemoTable(FirstName) values('John');
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable(FirstName) values('Sam');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable(FirstName) values('John');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable(FirstName) values('John');
Query OK, 1 row affected (0.10 sec)
mysql> insert into DemoTable(FirstName) values('Larry');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable(FirstName) values('Mike');
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable(FirstName) values('Robert');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable(FirstName) values('Carol');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable(FirstName) values('Mike');
Query OK, 1 row affected (0.12 sec)Following is the query to display records from the table using select command:
mysql> select *from DemoTable;
This will produce the following output:
+----+-----------+ | Id | FirstName | +----+-----------+ | 1 | Larry | | 2 | John | | 3 | Sam | | 4 | John | | 5 | John | | 6 | Larry | | 7 | Mike | | 8 | Robert | | 9 | Carol | | 10 | Mike | +----+-----------+ 10 rows in set (0.00 sec)
Following is the query to ignore duplicate rows in COUNT and get the count of only unique rows:
mysql> select count(distinct FirstName) from DemoTable;
This will produce the following output:
+---------------------------+ | count(distinct FirstName) | +---------------------------+ | 6 | +---------------------------+ 1 row in set (0.03 sec)
Updated on: 30-Jul-2019
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