Methods for modifying table structure in MySQL database: 1. Use add to add fields and use drop to delete fields; 2. Use alter to modify field names; 3. Modify column types; 4. Modify table names; 5. Modify tables Option; 6. Modify column attributes.
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MySQL database modification table structure Method:
1. Add and delete fields
(1), add
Alter table table name add[column] field Name column type column attribute [first|after field name]
(2), delete
Alter table table name drop[column] field name;
2. Modify the field name
Statement: alter table table name change original field name new field name column type column attribute;
Note: Even if only the field name is modified, the original type and original attributes of the field must be rewritten, otherwise they will be deleted.
3. Modify column type
Statement: alter table table name modify field name column type column attribute;
4. Modify the table name
Statement: alter table table name rename to new table name;
5. Modify table options
Statement: alter table table name table option;
Description: Although MYSQL provides a command to modify table options, if If there is already data in a table, do not execute the command to modify the character set.
6. Modify column attributes
Column attributes include not null, default, unique, primary key, auto_increment
After a table is created, we can use alter table table name modify to operate column attributes. During operation, if the column attribute is written, the column attribute is added; if not, the column attribute is deleted.
Special column attributes: Primary key and unique.
Add column attributes
Add common attributes:
Statement: alter table table name modify field name column type column attribute;
Note:
A. When adding auto_increment, please note that the field must be an integer, and it must be a unique or primary key.
B. Unique and default cannot be used together.
Add primary key attributes:
Statement: alter table table name add primary key (field name);
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