问题
I need to remove a unique key from my mysql table. How can remove that using mysql query.
I tried this but it is not working
alter table tbl_quiz_attempt_master drop unique key;
Please help me
Thanks
回答1:
All keys are named, you should use something like this -
ALTER TABLE tbl_quiz_attempt_master
DROP INDEX index_name;
To drop primary key use this one -
ALTER TABLE tbl_quiz_attempt_master
DROP INDEX `PRIMARY`;
ALTER TABLE Syntax.
回答2:
First you need to know the exact name of the INDEX (Unique key in this case) to delete or update it.
INDEX names are usually same as column names. In case of more than one INDEX applied on a column, MySQL automatically suffixes numbering to the column names to create unique INDEX names.
For example if 2 indexes are applied on a column named customer_id
- The first index will be named as
customer_iditself. - The second index will be names as
customer_id_2and so on.
To know the name of the index you want to delete or update
SHOW INDEX FROM <table_name>
as suggested by @Amr
To delete an index
ALTER TABLE <table_name> DROP INDEX <index_name>;
回答3:
ALTER TABLE mytable DROP INDEX key_Name;
回答4:
For those who don't know how to get index_name which mentioned in Devart's answer, or key_name which mentioned in Uday Sawant's answer, you can get it like this:
SHOW INDEX FROM table_name;
This will show all indexes for the given table, then you can pick name of the index or unique key that you want to remove.
回答5:
Unique key is actually an index. http://codeghar.wordpress.com/2008/03/28/drop-unique-constraint-in-mysql/
回答6:
There are two method two remove index in mysql. First method is GUI. In this method you have to open GUI interface of MYSQL and then go to that database and then go to that particular table in which you want to remove index.
After that click on the structure option, Then you can see table structure and below you can see table indexes. You can remove indexes by clicking on drop option
Second method by
ALTER TABLE student_login_credentials DROP INDEX created_at;
here student_login_credentials is table name and created_at is column name
回答7:
To add a unique key use :
alter table your_table add UNIQUE(target_column_name);
To remove a unique key use:
alter table your_table drop INDEX target_column_name;
来源：https://stackoverflow.com/questions/9172164/how-to-remove-unique-key-from-mysql-table