MySQL Basics five--data modification

1. Add a single column

ALTER table tab_red (table name) ADD age (column name) INT (column type) constraint {first| After Dname (after the Dname column)};

ALTER TABLE tab_red ADD age INT not NULL DEFAULT 10;

2. Add multiple columns

ALTER table tab_red (table name) ADD (dname varchar (), age int unsigned);

Adding multiple columns Cannot set the position of a column, and cannot be placed between the first column and a column. Only default in the last.

3. Delete a single column

ALTER table tab_red (table name) DROP dname (column name);

4. Delete multiple columns

ALTER table tab_red (table name) DROP Dname,drop age;

5. Deleting columns while adding a new column

ALTER TABLE tab_red DROP dname,add age INT;

6. Add a PRIMARY key

Alter TABLE tab_red ALTER DNAME set default Literal/drop default;

7. Delete a PRIMARY KEY constraint

ALTER TABLE tab_red DROP PRIMARY KEY;

MySQL Basics five--data modification