[DERBY-1926] Provide documentation for ALTER TABLE DROP COLUMN

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 10.3.1.4
• Fix Version/s: 10.3.1.4
• Component/s: Documentation
• Assignee: Bryan Pendleton
• Reporter: Bryan Pendleton
• Created: 04/Oct/06 03:05
• Updated: 01/Jul/09 00:34
• Resolved: 11/Oct/06 16:52

Description

The documentation will need to be updated after DERBY-1489 is committed. The reference manual will need to describe how to use the new ALTER TABLE DROP COLUMN feature to drop a column from a table.

The documentation for the ALTER TABLE command is becoming somewhat unwieldy, so perhaps there is a way to restructure the page to make it easier and more approachable.

In the documentation, it will be important to clearly describe the RESTRICT and CASCADE behaviors, as users may be confused by what things cause RESTRICT to refuse to drop a column. The comments in AlterTableConstantAction.java may help.

Specifically, the documentation should note these possibly unexpected behaviors:

• If a column is present in one or more indexes, these indexes by themselves do not cause
  RESTRICT to refuse to drop a column. Instead, the column will simply be dropped from
  the index, and if that was the last column in that index, the entire index will be dropped.
• Explicitly named CHECK constraints will cause RESTRICT to refuse to drop a column, as
  will PRIMARY KEY, FOREIGN KEY, and UNIQUE constrants. However, an unnamed simple
  NOT NULL constraint on a column will NOT cause RESTRICT to refuse to drop it.

Issue Links

• depends upon: DERBY-1489 Provide ALTER TABLE DROP COLUMN functionality