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Overview
| 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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| Timelines: | family | ancestors | descendants | both | trunk |
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| SHA3-256: |
998c5310ebb9d6e181f866f60883d512 |
| User & Date: | drh 2019-10-21 14:57:02 |
Context
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2019-10-22
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| 13:26 | Fix a typo on the whentouse.html page. (check-in: 8b5ba0e2b1 user: drh tags: trunk) | |
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2019-10-21
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| 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) | |
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2019-10-18
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| 02:16 | Fix a typo in the "quirks.html" document. (check-in: 7dce3c2f8a user: drh tags: trunk) | |
Changes
Changes to pages/lang.in.
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</tcl> <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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</tcl> <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> |