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Overview
| Comment: | In the "lang.html" documentation file, put the CREATE TRIGGER and DROP TRIGGER sections in alphabetical order. (CVS 564) |
|---|---|
| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA1: |
d1d8642b57bd0765ade730248012d58b |
| User & Date: | drh 2002-05-15 11:43:16 |
Context
|
2002-05-15
| ||
| 11:44 | Remove all tabs from the beginning of source code lines. Replace tabs with the appropriate number of spaces. (CVS 565) (check-in: 690f9a16 user: drh tags: trunk) | |
| 11:43 | In the "lang.html" documentation file, put the CREATE TRIGGER and DROP TRIGGER sections in alphabetical order. (CVS 564) (check-in: d1d8642b user: drh tags: trunk) | |
| 08:43 | Add the Makefile.in that was forgotten with checkin #562 (CVS 563) (check-in: 29b8330c user: danielk1977 tags: trunk) | |
Changes
Changes to www/lang.tcl.
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#
# Run this Tcl script to generate the sqlite.html file.
#
set rcsid {$Id: lang.tcl,v 1.34 2002/05/15 08:30:15 danielk1977 Exp $}
puts {<html>
<head>
<title>Query Language Understood By SQLite</title>
</head>
<body bgcolor=white>
<h1 align=center>
................................................................................
are read from the <b>sqlite_master</b> table and used to regenerate
SQLite's internal representation of the table layout.
If the original command was a CREATE TABLE AS then then an equivalent
CREATE TABLE statement is synthesized and store in <b>sqlite_master</b>
in place of the original command.
</p>
}
Section {CREATE VIEW} {createview}
Syntax {sql-command} {
CREATE VIEW <view-name> AS <select-statement>
}
................................................................................
}
Section {DROP TABLE} droptable
Syntax {sql-command} {
DROP TABLE <table-name>
}
puts {
<p>The DROP TABLE statement consists of the keywords "DROP TABLE" followed
by the name of the table. The table named is completely removed from
the disk. The table can not be recovered. All indices associated with
the table are also deleted.</p>}
................................................................................
In version 1.0 of SQLite, the VACUUM command would invoke
<b>gdbm_reorganize()</b> to clean up the backend database file.
Beginning with version 2.0 of SQLite, GDBM is no longer used for
the database backend and VACUUM has become a no-op.
</p>
}
Section {CREATE TRIGGER} createtrigger
Syntax {sql-statement} {
CREATE TRIGGER <trigger-name> [ BEFORE | AFTER ]
<database-event>
<trigger-action>
}
Syntax {database-event} {
DELETE |
INSERT |
UPDATE |
UPDATE OF <column-list>
ON <table-name>
}
Syntax {trigger-action} {
[ FOR EACH ROW ] [ WHEN <expression> ]
BEGIN
<trigger-step> ; [ <trigger-step> ; ]*
END
}
Syntax {trigger-step} {
<update-statement> | <insert-statement> |
<delete-statement> | <select-statement>
}
puts {
<p>The CREATE TRIGGER statement is used to add triggers to the
database schema. Triggers are database operations (the <i>trigger-action</i>)
that are automatically performed when a specified database event (the
<i>database-event</i>) 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 of one or more
specified columns of a table are updated.</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 as <i>trigger-steps</i>
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>
<p>Both the WHEN clause and the <i>trigger-steps</i> may access elements of
the row being inserted, deleted or updated using references of the form
"NEW.<i>column-name</i>" and "OLD.<i>column-name</i>", where
<i>column-name</i> is the name of a column from the table that the trigger
is associated with. OLD and NEW references may only be used in triggers on
<i>trigger-event</i>s for which they are relevant, as follows:</p>
<table border=0 cellpadding=10>
<tr>
<td valign="top" align="right" width=120><i>INSERT</i></td>
<td valign="top">NEW references are valid</td>
</tr>
<tr>
<td valign="top" align="right" width=120><i>UPDATE</i></td>
<td valign="top">NEW and OLD references are valid</td>
</tr>
<tr>
<td valign="top" align="right" width=120><i>DELETE</i></td>
<td valign="top">OLD references are valid</td>
</tr>
</table>
</p>
<p>If a WHEN clause is supplied, the SQL statements specified as <i>trigger-steps</i> are only executed for rows for which the WHEN clause is true. If no WHEN clause is supplied, the SQL statements are executed for all rows.</p>
<p>The specified <i>trigger-time</i> determines when the <i>trigger-steps</i>
will be executed relative to the insertion, modification or removal of the
associated row.</p>
<p>An ON CONFLICT clause may be specified as part of an UPDATE or INSERT
<i>trigger-step</i>. However if an ON CONFLICT clause is specified as part of
the statement causing the trigger to fire, then this conflict handling
policy is used instead.</p>
<p>Triggers are automatically dropped when the table that they are
associated with is dropped.</p>
<p>Triggers may be created on views, as well as ordinary tables. If one or
more INSERT, DELETE or UPDATE triggers are defined on a view, then it is not
an error to execute an INSERT, DELETE or UPDATE statement on the view,
respectively. Thereafter, executing an INSERT, DELETE or UPDATE on the view
causes the associated triggers to fire. The real tables underlying the view
are not modified (except possibly explicitly, by a trigger program).</p>
<p><b>Example:</b></p>
<p>Assuming that customer records are stored in the "customers" table, and
that order records are stored in the "orders" table, the following trigger
ensures that all associated orders are redirected when a customer changes
his or her address:</p>
}
Example {
CREATE TRIGGER update_customer_address UPDATE OF address ON customers
BEGIN
UPDATE orders SET address = new.address WHERE customer_name = old.name;
END;
}
puts {
<p>With this trigger installed, executing the statement:</p>
}
Example {
UPDATE customers SET address = '1 Main St.' WHERE name = 'Jack Jones';
}
puts {
<p>causes the following to be automatically executed:</p>
}
Example {
UPDATE orders SET address = '1 Main St.' WHERE customer_name = 'Jack Jones';
}
Section {DROP TRIGGER} droptrigger
Syntax {sql-statement} {
DROP TRIGGER <trigger-name>
}
puts {
<p>Used to drop a trigger from the database schema. Note that triggers
are automatically dropped when the associated table is dropped.</p>
}
puts {
<p><hr /></p>
<p><a href="index.html"><img src="/goback.jpg" border=0 />
Back to the SQLite Home Page</a>
</p>
</body></html>}
|
| > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < |
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#
# Run this Tcl script to generate the sqlite.html file.
#
set rcsid {$Id: lang.tcl,v 1.35 2002/05/15 11:43:16 drh Exp $}
puts {<html>
<head>
<title>Query Language Understood By SQLite</title>
</head>
<body bgcolor=white>
<h1 align=center>
................................................................................
are read from the <b>sqlite_master</b> table and used to regenerate
SQLite's internal representation of the table layout.
If the original command was a CREATE TABLE AS then then an equivalent
CREATE TABLE statement is synthesized and store in <b>sqlite_master</b>
in place of the original command.
</p>
}
Section {CREATE TRIGGER} createtrigger
Syntax {sql-statement} {
CREATE TRIGGER <trigger-name> [ BEFORE | AFTER ]
<database-event> ON <table-name>
<trigger-action>
}
Syntax {database-event} {
DELETE |
INSERT |
UPDATE |
UPDATE OF <column-list>
}
Syntax {trigger-action} {
[ FOR EACH ROW ] [ WHEN <expression> ]
BEGIN
<trigger-step> ; [ <trigger-step> ; ]*
END
}
Syntax {trigger-step} {
<update-statement> | <insert-statement> |
<delete-statement> | <select-statement>
}
puts {
<p>The CREATE TRIGGER statement is used to add triggers to the
database schema. Triggers are database operations (the <i>trigger-action</i>)
that are automatically performed when a specified database event (the
<i>database-event</i>) 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 of one or more
specified columns of a table are updated.</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 as <i>trigger-steps</i>
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>
<p>Both the WHEN clause and the <i>trigger-steps</i> may access elements of
the row being inserted, deleted or updated using references of the form
"NEW.<i>column-name</i>" and "OLD.<i>column-name</i>", where
<i>column-name</i> is the name of a column from the table that the trigger
is associated with. OLD and NEW references may only be used in triggers on
<i>trigger-event</i>s for which they are relevant, as follows:</p>
<table border=0 cellpadding=10>
<tr>
<td valign="top" align="right" width=120><i>INSERT</i></td>
<td valign="top">NEW references are valid</td>
</tr>
<tr>
<td valign="top" align="right" width=120><i>UPDATE</i></td>
<td valign="top">NEW and OLD references are valid</td>
</tr>
<tr>
<td valign="top" align="right" width=120><i>DELETE</i></td>
<td valign="top">OLD references are valid</td>
</tr>
</table>
</p>
<p>If a WHEN clause is supplied, the SQL statements specified as <i>trigger-steps</i> are only executed for rows for which the WHEN clause is true. If no WHEN clause is supplied, the SQL statements are executed for all rows.</p>
<p>The specified <i>trigger-time</i> determines when the <i>trigger-steps</i>
will be executed relative to the insertion, modification or removal of the
associated row.</p>
<p>An ON CONFLICT clause may be specified as part of an UPDATE or INSERT
<i>trigger-step</i>. However if an ON CONFLICT clause is specified as part of
the statement causing the trigger to fire, then this conflict handling
policy is used instead.</p>
<p>Triggers are automatically dropped when the table that they are
associated with is dropped.</p>
<p>Triggers may be created on views, as well as ordinary tables. If one or
more INSERT, DELETE or UPDATE triggers are defined on a view, then it is not
an error to execute an INSERT, DELETE or UPDATE statement on the view,
respectively. Thereafter, executing an INSERT, DELETE or UPDATE on the view
causes the associated triggers to fire. The real tables underlying the view
are not modified (except possibly explicitly, by a trigger program).</p>
<p><b>Example:</b></p>
<p>Assuming that customer records are stored in the "customers" table, and
that order records are stored in the "orders" table, the following trigger
ensures that all associated orders are redirected when a customer changes
his or her address:</p>
}
Example {
CREATE TRIGGER update_customer_address UPDATE OF address ON customers
BEGIN
UPDATE orders SET address = new.address WHERE customer_name = old.name;
END;
}
puts {
<p>With this trigger installed, executing the statement:</p>
}
Example {
UPDATE customers SET address = '1 Main St.' WHERE name = 'Jack Jones';
}
puts {
<p>causes the following to be automatically executed:</p>
}
Example {
UPDATE orders SET address = '1 Main St.' WHERE customer_name = 'Jack Jones';
}
Section {CREATE VIEW} {createview}
Syntax {sql-command} {
CREATE VIEW <view-name> AS <select-statement>
}
................................................................................
}
Section {DROP TABLE} droptable
Syntax {sql-command} {
DROP TABLE <table-name>
}
Section {DROP TRIGGER} droptrigger
Syntax {sql-statement} {
DROP TRIGGER <trigger-name>
}
puts {
<p>Used to drop a trigger from the database schema. Note that triggers
are automatically dropped when the associated table is dropped.</p>
}
puts {
<p>The DROP TABLE statement consists of the keywords "DROP TABLE" followed
by the name of the table. The table named is completely removed from
the disk. The table can not be recovered. All indices associated with
the table are also deleted.</p>}
................................................................................
In version 1.0 of SQLite, the VACUUM command would invoke
<b>gdbm_reorganize()</b> to clean up the backend database file.
Beginning with version 2.0 of SQLite, GDBM is no longer used for
the database backend and VACUUM has become a no-op.
</p>
}
puts {
<p><hr /></p>
<p><a href="index.html"><img src="/goback.jpg" border=0 />
Back to the SQLite Home Page</a>
</p>
</body></html>}
|