SQL Server Database Tutorial Three, add, delete, modify, table column

To modify the table design of a database, you can use the SQL ALTER TABLE statement, which is used to add, delete, or modify table columns in an existing table.

　　1> add a new column to the database table:

Grammar:

ALTER table name ADD column name data type

For example: Add a new column birthday in the persons table below, with a data type of varchar (50)

Enter the following syntax in the new query:

ALTER TABLE ADD varchar (+)

The results after insertion are as follows:

2> to delete columns from a table in a database table:

Grammar:

ALTER table table name DROP column name

For example:

Delete the table design of the Birthday column in the persons table, and this column of data is also deleted.

ALTER TABLE DROP Birthday

3> Changing the database table data type:

This statement is used to change the data type of a column of data in a database when the database is designed.

Grammar:

Alter TAVLE table name ALTER COLUMN name new data type

For example:

In the previous persons table, the birthday data type is varchar (50), but now to change the data type to the text type, the statement is as follows:

ALTER TABLE ALTER text

SQL Server Database Tutorial Three, add, delete, modify, table column