Download SQL: ALTER Command - Modifying Table Structures and more Assignments Database Programming in PDF only on Docsity!
SQL: ALTER command
alter command is used for altering the table structure, such as, to add a column to existing table to rename any existing column to change datatype of any column or to modify its size. to drop a column from the table.
ALTER Command: Add a new Column
Using ALTER command we can add a column to any existing table. Following is the syntax, ALTER TABLE table_name ADD( column_name datatype); Here is an Example for this, ALTER TABLE student ADD( address VARCHAR( 200 ) ); The above command will add a new column address to the table student , which will hold data of type varchar which is nothing but string, of length 200.
ALTER Command: Add multiple new Columns
Using ALTER command we can even add multiple new columns to any existing table. Following is the syntax, ALTER TABLE table_name ADD( column_name1 datatype1, column-name2 datatype2, column-name3 datatype3); Here is an Example for this, ALTER TABLE student ADD( father_name VARCHAR( 60 ), mother_name VARCHAR( 60 ), dob DATE); The above command will add three new columns to the student table
ALTER Command: Add Column with default value
Here is an Example for this, ALTER TABLE student MODIFY( address varchar( 300 )); Remember we added a new column address in the beginning? The above command will modify the address column of the student table, to now hold upto 300 characters.
ALTER Command: Rename a Column
Using ALTER command you can rename an existing column. Following is the syntax, ALTER TABLE table_name RENAME old_column_name TO new_column_name; Here is an example for this, ALTER TABLE student RENAME address TO location; The above command will rename address column to location.
ALTER Command: Drop a Column
ALTER command can also be used to drop or remove columns. Following is the syntax, ALTER TABLE table_name DROP( column_name); Here is an example for this, ALTER TABLE student DROP( address); The above command will drop the address column from the table student.
