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Need help in deleting duplicate columns from a table in MySQL?
To delete duplicate columns, use DELETE with INNER JOIN. Following is the syntax −
delete tbl1 from yourTableName anyAliasName1 inner join yourTableName anyAliasName2 where yourCondition1 and yourCondition2
Let us create a table −
mysql> create table demo14 −> ( −> id int not null auto_increment primary key, −> name varchar(30) −> ); Query OK, 0 rows affected (1.89 sec)
Insert some records into the table with the help of insert command −
mysql> insert into demo14(name) values('John');
Query OK, 1 row affected (0.14 sec)
mysql> insert into demo14(name) values('David');
Query OK, 1 row affected (0.18 sec)
mysql> insert into demo14(name) values('David');
Query OK, 1 row affected (0.09 sec)
mysql> insert into demo14(name) values('Bob');
Query OK, 1 row affected (0.15 sec)
mysql> insert into demo14(name) values('John');
Query OK, 1 row affected (0.45 sec)
mysql> insert into demo14(name) values('Carol');
Query OK, 1 row affected (0.16 sec)Display records from the table using select statement −
mysql> select *from demo14;
This will produce the following output −
+----+-------+ | id | name | +----+-------+ | 1 | John | | 2 | David | | 3 | David | | 4 | Bob | | 5 | John | | 6 | Carol | +----+-------+ 6 rows in set (0.00 sec)
Following is the query to delete duplicate columns from the table −
mysql> delete tbl1 from demo14 tbl1 −> inner join demo14 tbl2 −> where −> tbl1.id < tbl2.id and −> tbl1.name = tbl2.name −> ; Query OK, 2 rows affected (0.20 sec)
Display records from the table using select statement −
mysql> select *from demo14;
This will produce the following output −
+----+-------+ | id | name | +----+-------+ | 3 | David | | 4 | Bob | | 5 | John | | 6 | Carol | +----+-------+ 4 rows in set (0.00 sec)
Updated on: 19-Nov-2020
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