SQL ALTER TABLE syntax

to add columns to a table, use the following syntax:

ALTER TABLE TABLE_NAMEADD COLUMN_NAME datatype

To delete a column from a table, use the following syntax:

ALTER TABLE table_name DROP COLUMN column_name

To change the data type of a column in a table, use the following syntax:

ALTER TABLE table_namealter COLUMN column_name datatype

If you want to add a column to a table that has already been built, you can use the following example:

ALTER TABLE t1 add column addr varchar (a) not null;

This statement adds a column of addr to the existing table T1, which is the last column in the table. If we want to add a column in the specified, you can use:

ALTER TABLE t1 add column addr varchar (NO) null after User1;

Note that the above command means adding addr to the column after User1. If you want to add to the first column, you can use:

ALTER TABLE t1 add column addr varchar (a) not NULL first;

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SQL ALTER TABLE syntax