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From "Bryan Pendleton (JIRA)" <derby-...@db.apache.org>
Subject [jira] Created: (DERBY-1926) Provide documentation for ALTER TABLE DROP COLUMN
Date Wed, 04 Oct 2006 03:05:20 GMT
Provide documentation for ALTER TABLE DROP COLUMN

                 Key: DERBY-1926
                 URL: http://issues.apache.org/jira/browse/DERBY-1926
             Project: Derby
          Issue Type: New Feature
          Components: Documentation
    Affects Versions:
            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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