How to select distinct rows without using group by statement

Question

A B C
1 1 1 
1 1 1 
2 2 2 
2 2 2 
3 3 3 
3 3 3 
4 4 4 
4 4 4 
5 5 5 
5 5 5 
5 5 5 
6 6 6
6 6 6 

I am to output only the distinct rows without using

Answer 1

This may totally shock you but MySQL uses GROUP BY under the hood to execute DISTINCT !!!

Here is something you may want to try

If the table is called mytable, do these two things:

First run this

ALTER TABLE mytable ADD INDEX ABC (A,B,C);`

Second, run this query

SELECT A,B,C FROM mytable GROUP BY A,B,C;

GROUP BY actually works better with an index present !!!

Here is sample code to prove it works

mysql> drop database if exists cool_cs;
Query OK, 1 row affected (0.04 sec)

mysql> create database cool_cs;
Query OK, 1 row affected (0.00 sec)

mysql> use cool_cs
Database changed
mysql> create table mytable
    -> (A int,B int,C int, key ABC (A,B,C));
Query OK, 0 rows affected (0.08 sec)

mysql> INSERt INTO mytable VALUES
    -> (1,1,1),(1,1,1),(2,2,2),(2,2,2),(3,3,3),
    -> (3,3,3),(4,4,4),(4,4,4),(5,5,5),(5,5,5),
    -> (5,5,5),(6,6,6),(6,6,6);
Query OK, 13 rows affected (0.06 sec)
Records: 13  Duplicates: 0  Warnings: 0

mysql> select a,b,c FROM mytable group by a,b,c;
+------+------+------+
| a    | b    | c    |
+------+------+------+
|    1 |    1 |    1 |
|    2 |    2 |    2 |
|    3 |    3 |    3 |
|    4 |    4 |    4 |
|    5 |    5 |    5 |
|    6 |    6 |    6 |
+------+------+------+
6 rows in set (0.02 sec)

mysql>

Give it a Try !!!