Mysql trigger update android 9

Триггеры в MySQL

Синтаксис создания триггера:

CREATE TRIGGER trigger_name trigger_time trigger_event
ON tbl_name FOR EACH ROW trigger_stmt * This source code was highlighted with Source Code Highlighter .

Применение

— таблица, за которой мы будем следить
CREATE TABLE `test` (
`id` INT ( 11 ) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`content` TEXT NOT NULL
) ENGINE = MYISAM
— лог
CREATE TABLE `log` (
`id` INT ( 11 ) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`msg` VARCHAR ( 255 ) NOT NULL ,
` time ` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ,
`row_id` INT ( 11 ) NOT NULL
) ENGINE = MYISAM
— триггер
DELIMITER |
CREATE TRIGGER `update_test` AFTER INSERT ON `test`
FOR EACH ROW BEGIN
INSERT INTO log Set msg = ‘insert’ , row_id = NEW .id;
END ; * This source code was highlighted with Source Code Highlighter .

Расширенный лог:

— Удаляем триггер
DROP TRIGGER `update_test`;
— Cоздадим еще одну таблицу,
— в которой будут храниться резервные копии строк из таблицы test
CREATE TABLE `testing`.` backup ` (
`id` INT ( 11 ) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`row_id` INT ( 11 ) UNSIGNED NOT NULL ,
`content` TEXT NOT NULL
) ENGINE = MYISAM
— триггеры
DELIMITER |
CREATE TRIGGER `update_test` before update ON `test`
FOR EACH ROW BEGIN
INSERT INTO backup Set row_id = OLD .id, content = OLD .content;
END ;

CREATE TRIGGER `delete_test` before delete ON `test`
FOR EACH ROW BEGIN
INSERT INTO backup Set row_id = OLD .id, content = OLD .content;
END * This source code was highlighted with Source Code Highlighter .

Теперь если мы отредактируем или удалим строку из test она скопируется в backup.

зы: надеюсь статья была интересной и полезной
UPD: для создания триггеров в версии до 5.1.6 требуются полномочия суперпользователя.

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MySQL AFTER UPDATE Trigger

Summary: in this tutorial, you will learn how to create a MySQL AFTER UPDATE trigger to log the changes made to a table.

Introduction to MySQL AFTER UPDATE triggers

MySQL AFTER UPDATE triggers are invoked automatically after an update event occurs on the table associated with the triggers.

The following shows the syntax of creating a MySQL AFTER UPDATE trigger:

First, specify the name of the trigger that you want to create in the CREATE TRIGGER clause.

Second, use AFTER UPDATE clause to specify the time to invoke the trigger.

Third, specify the name of the table to which the trigger belongs after the ON keyword.

Finally, specify the trigger body which consists of one or more statements.

If the trigger body has more than one statement, you need to use the BEGIN END block. And, you also need to change the default delimiter as shown in the following code:

In a AFTER UPDATE trigger, you can access OLD and NEW rows but cannot update them.

MySQL AFTER UPDATE trigger example

Let’s look at an example of creating a AFTER UPDATE trigger.

Setting up a sample table

First, create a table called Sales :

Second, insert sample data into the Sales table:

Third, query data from the Sales table to display its contents:

Finally, create a table that stores the changes in the quantit y column from the sales table:

Creating AFTER UPDATE trigger example

The following statement creates an AFTER UPDATE trigger on the sales table:

This after_sales_update trigger is automatically fired before an update event occurs for each row in the sales table.

If you update the value in the quantity column to a new value the trigger insert a new row to log the changes in the SalesChanges table.

Let’s examine the trigger in detail:

First, the name of the trigger is after_sales_update specified in the CREATE TRIGGER clause:

Second, the triggering event is:

Third, the table that the trigger associated with is sales :

Finally, use the IF-THEN statement inside the trigger body to check if the new value is not the same as the old one, then insert the changes into the SalesChanges table:

Testing the MySQL AFTER UPDATE trigger

First, update the quantity of the row with id 1 to 350:

The after_sales_update was invoked automatically.

Second, query data from the SalesChanges table:

Third, increase the sales quantity of all rows to 10%:

Fourth, query data from the SalesChanges table:

The trigger fired three times because of the updates of the three rows.

In this tutorial, you have learned how to create a MySQL AFTER UPDATE trigger to validate data before it is updated to a table.

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Mysql trigger update android 9

Here is a simple example that associates a trigger with a table, to activate for INSERT operations. The trigger acts as an accumulator, summing the values inserted into one of the columns of the table.

The CREATE TRIGGER statement creates a trigger named ins_sum that is associated with the account table. It also includes clauses that specify the trigger action time, the triggering event, and what to do when the trigger activates:

The keyword BEFORE indicates the trigger action time. In this case, the trigger activates before each row inserted into the table. The other permitted keyword here is AFTER .

The keyword INSERT indicates the trigger event; that is, the type of operation that activates the trigger. In the example, INSERT operations cause trigger activation. You can also create triggers for DELETE and UPDATE operations.

The statement following FOR EACH ROW defines the trigger body; that is, the statement to execute each time the trigger activates, which occurs once for each row affected by the triggering event. In the example, the trigger body is a simple SET that accumulates into a user variable the values inserted into the amount column. The statement refers to the column as NEW.amount which means “ the value of the amount column to be inserted into the new row. ”

To use the trigger, set the accumulator variable to zero, execute an INSERT statement, and then see what value the variable has afterward:

In this case, the value of @sum after the INSERT statement has executed is 14.98 + 1937.50 — 100 , or 1852.48 .

To destroy the trigger, use a DROP TRIGGER statement. You must specify the schema name if the trigger is not in the default schema:

If you drop a table, any triggers for the table are also dropped.

Trigger names exist in the schema namespace, meaning that all triggers must have unique names within a schema. Triggers in different schemas can have the same name.

It is possible to define multiple triggers for a given table that have the same trigger event and action time. For example, you can have two BEFORE UPDATE triggers for a table. By default, triggers that have the same trigger event and action time activate in the order they were created. To affect trigger order, specify a clause after FOR EACH ROW that indicates FOLLOWS or PRECEDES and the name of an existing trigger that also has the same trigger event and action time. With FOLLOWS , the new trigger activates after the existing trigger. With PRECEDES , the new trigger activates before the existing trigger.

For example, the following trigger definition defines another BEFORE INSERT trigger for the account table:

This trigger, ins_transaction , is similar to ins_sum but accumulates deposits and withdrawals separately. It has a PRECEDES clause that causes it to activate before ins_sum ; without that clause, it would activate after ins_sum because it is created after ins_sum .

Within the trigger body, the OLD and NEW keywords enable you to access columns in the rows affected by a trigger. OLD and NEW are MySQL extensions to triggers; they are not case-sensitive.

In an INSERT trigger, only NEW. col_name can be used; there is no old row. In a DELETE trigger, only OLD. col_name can be used; there is no new row. In an UPDATE trigger, you can use OLD. col_name to refer to the columns of a row before it is updated and NEW. col_name to refer to the columns of the row after it is updated.

A column named with OLD is read only. You can refer to it (if you have the SELECT privilege), but not modify it. You can refer to a column named with NEW if you have the SELECT privilege for it. In a BEFORE trigger, you can also change its value with SET NEW. col_name = value if you have the UPDATE privilege for it. This means you can use a trigger to modify the values to be inserted into a new row or used to update a row. (Such a SET statement has no effect in an AFTER trigger because the row change has already occurred.)

In a BEFORE trigger, the NEW value for an AUTO_INCREMENT column is 0, not the sequence number that is generated automatically when the new row actually is inserted.

By using the BEGIN . END construct, you can define a trigger that executes multiple statements. Within the BEGIN block, you also can use other syntax that is permitted within stored routines such as conditionals and loops. However, just as for stored routines, if you use the mysql program to define a trigger that executes multiple statements, it is necessary to redefine the mysql statement delimiter so that you can use the ; statement delimiter within the trigger definition. The following example illustrates these points. It defines an UPDATE trigger that checks the new value to be used for updating each row, and modifies the value to be within the range from 0 to 100. This must be a BEFORE trigger because the value must be checked before it is used to update the row:

It can be easier to define a stored procedure separately and then invoke it from the trigger using a simple CALL statement. This is also advantageous if you want to execute the same code from within several triggers.

There are limitations on what can appear in statements that a trigger executes when activated:

The trigger cannot use the CALL statement to invoke stored procedures that return data to the client or that use dynamic SQL. (Stored procedures are permitted to return data to the trigger through OUT or INOUT parameters.)

The trigger cannot use statements that explicitly or implicitly begin or end a transaction, such as START TRANSACTION , COMMIT , or ROLLBACK . ( ROLLBACK to SAVEPOINT is permitted because it does not end a transaction.).

MySQL handles errors during trigger execution as follows:

If a BEFORE trigger fails, the operation on the corresponding row is not performed.

A BEFORE trigger is activated by the attempt to insert or modify the row, regardless of whether the attempt subsequently succeeds.

An AFTER trigger is executed only if any BEFORE triggers and the row operation execute successfully.

An error during either a BEFORE or AFTER trigger results in failure of the entire statement that caused trigger invocation.

For transactional tables, failure of a statement should cause rollback of all changes performed by the statement. Failure of a trigger causes the statement to fail, so trigger failure also causes rollback. For nontransactional tables, such rollback cannot be done, so although the statement fails, any changes performed prior to the point of the error remain in effect.

Triggers can contain direct references to tables by name, such as the trigger named testref shown in this example:

Suppose that you insert the following values into table test1 as shown here:

As a result, the four tables contain the following data:

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Update Trigger — Updating table other than trigger table

This is the current code for the databases and its specific triggers for the reminders table. What I am having difficulty doing is to select the specific name and extra from the user notes table from the specific noteid in the reminders table all within the update trigger.

The id and noteid are inserted into the reminders and search table when an insert happens, but I want to be able to update the search table with the specific name and extra from the user notes table, is this possible?

1 Answer 1

There are a few anomalies in the presented code, so I’ve worked with it, modified it a little so that it runs, and given enough of an example that you should be able to work with it to get it to do what you want.

The main problem here is that to update a table other than the one triggering the ON UPDATE trigger, it’s necessary to join tables, and SQLite doesn’t support such an update statement.

I used a nice little utility called SQLite Studio to re-create the scenario. It’s available here: http://sqlitestudio.pl/?act=download

Here’s the code I used to re-create your database:

I noticed that some of the ID columns were named _id , and others id , so I named them all _id . When the triggers were created, the code within didn’t catch that; instead I got a run-time error when the trigger executed.

In the triggers, note that I’ve added FOR EACH ROW to each of them. This allows each row that’s INSERTed or UPDATEd to be processed, rather than just doing one blanket update statement per execution. I also omitted the update of the ID column in searchTable , as the update set the column value to be itself.

Here is the trigger creation DDL:

I tested creating records in the userNotesTable . Then, when I created some records in the userRemindersTable , the INSERT trigger fired and inserted a corresponding record into the searchTable .

When the records in userRemindersTable are updated, the name and extra fields in searchTable are set based on the corresponding noteid .

I’m assuming that there are some omitted fields in userRemindersTable , as there’s not really anything to update (to test, I updated the _id field). Further, for the INSERT trigger, I deliberately left out the setting of the name and extra fields, as they were not mentioned in the question, although they probably also need to be added to the INSERT statement in the ON INSERT trigger.

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