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Comment:Update the CREATE TRIGGER documentation to acknowledge the fact that columns in the UPDATE OF syntax of CREATE TRIGGER need not exist in the table, and that the trigger only fires if one of the columns named in the UPDATE OF clause appear on the left-hand side of one of the terms in the SET clause of the UPDATE statement.
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SHA3-256: 998c5310ebb9d6e181f866f60883d512dff66b16a177b9fce170e14a93fde18c
User & Date: drh 2019-10-21 14:57:02
Context
2019-10-22
13:26
Fix a typo on the whentouse.html page. check-in: 8b5ba0e2b1 user: drh tags: trunk
2019-10-21
14:57
Update the CREATE TRIGGER documentation to acknowledge the fact that columns in the UPDATE OF syntax of CREATE TRIGGER need not exist in the table, and that the trigger only fires if one of the columns named in the UPDATE OF clause appear on the left-hand side of one of the terms in the SET clause of the UPDATE statement. check-in: 998c5310eb user: drh tags: trunk
2019-10-18
02:16
Fix a typo in the "quirks.html" document. check-in: 7dce3c2f8a user: drh tags: trunk
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<p>^The CREATE TRIGGER statement is used to add triggers to the 
database schema. ^Triggers are database operations 
that are automatically performed when a specified database event
occurs.  </p>

<p>^A trigger may be specified to fire whenever a [DELETE], [INSERT],
or [UPDATE] of a
particular database table occurs, or whenever an [UPDATE] occurs on
on one or more specified columns of a table.</p>













<p>^At this time SQLite supports only FOR EACH ROW triggers, not FOR EACH
STATEMENT triggers. ^Hence explicitly specifying FOR EACH ROW is optional.
^FOR EACH ROW implies that the SQL statements specified in the trigger
may be executed (depending on the WHEN clause) for each database row being
inserted, updated or deleted by the statement causing the trigger to fire.</p>








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<p>^The CREATE TRIGGER statement is used to add triggers to the 
database schema. ^Triggers are database operations 
that are automatically performed when a specified database event
occurs.  </p>

<p>^Each trigger must specify that it will fire for one of
the following operations: [DELETE], [INSERT], [UPDATE].
The trigger fires once for each row that is deleted, inserted,
or updated.  If the "UPDATE OF <yyterm>column-name</yyterm>"
syntax is used, then the trigger will only fire if
<yyterm>column-name</yyterm> appears on the left-hand side of
one of the terms in the SET clause of the [UPDATE] statement.</p>

<p>Due to an historical oversight, columns named in the "UPDATE OF"
clause do not actually have to exist in the table being updated.
Unrecognized column names are silently ignored.
It would be more helpful if SQLite would fail the CREATE TRIGGER
statement if any of the names in the "UPDATE OF" clause are not
columns in the table.  However, as this problem was discovered
many years after SQLite was widely deployed, we have resisted
fixing the problem for fear of breaking legacy applications.</p>

<p>^At this time SQLite supports only FOR EACH ROW triggers, not FOR EACH
STATEMENT triggers. ^Hence explicitly specifying FOR EACH ROW is optional.
^FOR EACH ROW implies that the SQL statements specified in the trigger
may be executed (depending on the WHEN clause) for each database row being
inserted, updated or deleted by the statement causing the trigger to fire.</p>