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MySQL Count Distinct values process is very slow. How to fasten it?
To fasten the process, you can use INDEX. Let us first create a table −
mysql> create table DemoTable1905 ( FirstName varchar(20), LastName varchar(20) , INDEX F_L_Name(FirstName,LastName) ); Query OK, 0 rows affected (0.00 sec)
Insert some records in the table using insert command −
mysql> insert into DemoTable1905 values('John','Smith');
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1905 values('John','Doe');
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1905 values('Adam','Smith');
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1905 values('John','Doe');
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1905 values('Chris','Brown');
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1905 values('Adam','Smith');
Query OK, 1 row affected (0.00 sec)
Display all records from the table using select statement −
mysql> select * from DemoTable1905;
This will produce the following output −
+-----------+----------+ | FirstName | LastName | +-----------+----------+ | Adam | Smith | | Adam | Smith | | Chris | Brown | | John | Doe | | John | Doe | | John | Smith | +-----------+----------+ 6 rows in set (0.00 sec)
Here is the query to count distinct values −
mysql> select count(distinct FirstName) from DemoTable1905;
This will produce the following output −
+---------------------------+ | count(distinct FirstName) | +---------------------------+ | 3 | +---------------------------+ 1 row in set (0.00 sec)
Updated on: 2019-12-30T06:20:28+05:30
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