Provide documentation for ALTER TABLE DROP COLUMN
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Key: DERBY-1926
URL: http://issues.apache.org/jira/browse/DERBY-1926
Project: Derby
Issue Type: New Feature
Components: Documentation
Affects Versions: 10.3.0.0
Reporter: Bryan Pendleton
Priority: Minor
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.
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