MySQL knowledge points for the second-level computer exam mysql alter command

Usage of alter command in mysql to edit table structure. The specific contents are as follows

Modify field type

mysql> alter table employee change depno depno int(5) not null;

Add index

mysql> alter table table name add index index name (field name 1 [, field name 2 ...]);

example:

mysql> alter table employee add index emp_name (name);

Add the primary keyword index

mysql> alter table table name add primary key (field name);

example:

mysql> alter table employee add primary key(id);

Add unique restriction index

mysql> alter table table name add unique index name (field name);

example:

mysql> alter table employee add unique emp_name2(cardnumber);

View the index of a table

mysql> show index from table name;

example:

mysql> show index from employee;

Delete an index

mysql> alter table table name drop index index name;

example:

mysql>alter table employee drop index emp_name;

Modify table: add fields:

mysql> ALTER TABLE table_name ADD field_name field_type;

View the table:

mysql> SELECT * FROM table_name;

Modify the original field name and type:

mysql> ALTER TABLE table_name CHANGE old_field_name new_field_name field_type;

To delete a field:

ALTER TABLE table_name DROP field_name

The above is the full content of this article. I hope it will be helpful for everyone’s study. I also hope that everyone will support 123WORDPRESS.COM.

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