Alter Table Syntax

Once a table is created in the database, there are many occasions where one may wish to change the structure of the table. In general, the SQL syntax for ALTER TABLE is
ALTER TABLE "table_name"
[alter specification]
[alter specification] is dependent on the type of alteration we wish to perform. We list a number of common changes below:

ALTER TABLE Add Column

ALTER TABLE Modify Column

ALTER TABLE Rename Column

ALTER TABLE Drop Column

ALTER TABLE Add Index

ALTER TABLE Drop Index

ALTER TABLE Add Constraint

ALTER TABLE Drop Constraint

For all cases, examples are provided for MySQL, Oracle, and SQL Server.