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 the group by statement. I cannot use group by because it makes mysql hang. So it should return
1 1 1
2 2 2
3 3 3
4 4 4
5 5 5
6 6 6
Solutions:
If the name of your table is mytable , select distinct * from mytable will do the trick.
MySQL uses GROUP BY under the hood to execute DISTINCT !!!
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>
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 the group by statement. I cannot use group by because it makes mysql hang. So it should return
1 1 1
2 2 2
3 3 3
4 4 4
5 5 5
6 6 6
Solutions:
If the name of your table is mytable , select distinct * from mytable will do the trick.
MySQL uses GROUP BY under the hood to execute DISTINCT !!!
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>
0 comments:
Post a Comment