How to speed up SELECT DISTINCT in MySQL
To speed up SELECT DISTINCT, you can create an index on the column or set of columns. Let us first create a table −
mysql> create table DemoTable
(
Name varchar(40)
);
Query OK, 0 rows affected (1.13 sec)
Following is the query to create an index −
mysql> create index Name_Index on DemoTable(Name);
Query OK, 0 rows affected (1.56 sec)
Records: 0 Duplicates: 0 Warnings: 0
Insert some records in the table using insert command −
mysql> insert into DemoTable values('Chris');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('Mike');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable values('Chris');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('Chris');
Query OK, 1 row affected (0.12 sec)
mysql> insert into DemoTable values('Sam');
Query OK, 1 row affected (0.16 sec)Display all records from the table using select statement −
mysql> select *from DemoTable;
This will produce the following output −
+-------+
| Name |
+-------+
| Chris |
| Chris |
| Chris |
| Mike |
| Sam |
+-------+
5 rows in set (0.00 sec)
Following is the query for selecting only distinct records −
mysql> select distinct Name from DemoTable;
This will produce the following output −
+-------+
| Name |
+-------+
| Chris |
| Mike |
| Sam |
+-------+
3 rows in set (0.02 sec)
Published on 01-Oct-2019 12:13:03
