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The DROP Clause

The DROP colname clause deletes the specified column from the table.An attempt to drop a column will fail if anything references it.Consider the following items as sources of potential dependencies:

  • column or table constraints

  • indexes

  • stored procedures, functions and triggers

  • views

Effect on Version Count

  • Each time a column is dropped, the table’s metadata change counter is increased by one.

The DROP CONSTRAINT Clause

The DROP CONSTRAINT clause deletes the specified column-level or table-level constraint.

A PRIMARY KEY or UNIQUE key constraint cannot be deleted if it is referenced by a FOREIGN KEY constraint in another table.It will be necessary to drop that FOREIGN KEY constraint before attempting to drop the PRIMARY KEY or UNIQUE key constraint it references.

Effect on Version Count

  • Deleting a column constraint or a table constraint does not increase the metadata change counter.