Use the Add clause to add a column to an existing table. It is optional.
This clause adds a column to the end of the column list. It defines a column with the same syntax as the Create Table command (see "Column Definition for Local Tables"). If NOT NULL is specified and the table is not empty, a default value must be specified. In all other respects, this command is the equivalent of a column definition in a Create Table statement.
The optional Beforeexisting_column can be used to specify the name of an existing column so that the new column is inserted in a position just before the existing column.
The optional Beforeexisting_column can be used to specify the name of an existing column so that the new column is inserted in a position just before the existing column.
If a SQL view includes SELECT * FROM for the table to which the column was added in the view’s Select statement, the new column is added to the view.
Example A
Assuming the current schema is PUBLIC, this example adds the status column with a default value of ACTIVE to the test table.
ALTER TABLE test ADD COLUMN status VARCHAR(30) DEFAULT 'ACTIVE'
Example B
Assuming the current schema is PUBLIC, this example adds a deptId column that can be used as a foreign key column.
The optional Before existing_column can be used to specify the name of an existing column so that the new column is inserted in a position just before the existing column.