Introduction to SQL Triggers

Triggers in SQL, with no doubt, are one of the most innovative tools to manage and automate operations in the database. A trigger is a sort of stored procedure, which gets executed, or ‘fires’, on the occurrence of some events in a database. These events are related to actions like inserting, updating or deleting the data. Triggers in SQL are quite useful for implementing business controls, assuring data quality and standardizing work processes. Therefore, the efficient use of triggers is one of the important skills to acquire in the course of learning SQL.

Not only is the trigger concept something which is unfamiliar but it is also helpful once one gets the hang of it. Triggers are mechanisms through which the databases can respond to certain actions without any explicit request from the user or the application. For example, after inserting some data to a table, a trigger can update another table or validate the conditions under which the data is inserted.

What Is The Basic Structure Of SQL Triggers?

A trigger is set with conditions to be performed when certain changes are made in the database. These changes can be in the form of new addition of records, editing, or elimination of existing records. Now, whenever one of these changes takes place, the trigger fires up automatically with certain set conditions.

Triggers are set at a particular table and they get executed before or after recording of an event. Depending on the timing of the trigger, it can also stop the change to go ahead or allow the change to go ahead. In view of this, triggers are very useful as they guarantee that all specific conditions are satisfied prior to or following the changes made in the data.

As an illustration, it is common for a trigger to verify if an employee's salary lies somewhere between two values whilst updating the employee's details. Whenever a new salary is higher than the allowed one, the trigger may block the update from being retained. Similarly, a trigger could make sure that a specific field gets computed and its value updated every time another field is updated.

Types of SQL Triggers

It has been observed that SQL triggers can be classified according to when they are executed and during which event they execute.

1. Before Triggers

Such database triggers are executed before some element of an event occurs, for example, before a new record is inserted in a table a ‘before insert’ trigger runs. This particular kind of trigger is effective for modifying or ensuring the correctness of data before it is stored in a database. And, if some condition is not met, a trigger that is invoked before can prohibit its execution.

2. After Triggers

An after trigger will be executed after an event has taken place, for example, there is an after update trigger, which will be called after the completion of update operation. After triggers are utilized quite frequently for data auditing purposes, including changing logs or updating other tables after data is modified.

3. Paths Converting Triggers

Instead of triggers replacing the action, every time the action is performed, a custom action is performed for that time. This kind of trigger is relatively uncommon but is helpful in certain situations. To illustrate, an "instead of insert" trigger simply asserts that in case of insert a different operation will take place, say updating a certain row's values assuming a particular condition is true.

Benefits of Using Triggers In SQL

If their objectives and purposes are clear to a designer and user of a database, triggers can help in managing a wide variety of tasks. For example, they can be used to automate processes, maintain consistency of a database and or even mitigate the occurrence of particular errors.

1. Shed Work Load Didactic

These if set into conditions can automatically provide these defined actions regardless of user input. This can be quite advantageous for processes like table updates, notifications, or logging of templates whenever specified changes are made. Working these processes out can save lots of time and chances of human error by assigning them predefined job descriptions.

2. Implementation of Business Policies

The triggers can be set quite easily and consistently, which makes them suitable for use in consent management policy enforcement. If a business policy is enforced with the use of a forceful means, such as firing an employee who threatens company security, a trigger can be automatically activated which would prevent such a change from taking place. In this way, consent rules can be established and employed without much risk.

3. Data Protection Mechanism

A large number of triggers can be created and set as many as required to make the data in databases highly trustworthy. Before a change is made to a database, there are certain conditions that you may want to consider. This can be the use of a “before insert” trigger, where an “after update” would allow related tables or data to remain the same.

4. Modification History All Over the Place

The use of timestamps is integral since it gives financial and healthcare applications the required traceability. Modify every feature of a certain table or delete it and all relevant data such as the user who made the change and when it happened at. There is a good chance all applications will require data security and traceability support. Using triggers for traceability means the transaction log will hardly be sufficient.

Common Use Cases for SQL Triggers

SQL triggers are deployed in operations where alteration of data in one table makes it necessary to perform tasks in other parts of the system. It’s common for these types of use cases to revolve around the need to maintain data integrity and correctness.

1. Updating Related Tables

You can take an example of one table “price” and another product. If the price of a certain product in the products table changes, then there is also a trigger that works towards changing the total sales in the sales table, a requirement that needs to happen.

2. Preventing Invalid Data Modifications

Similarly, a trigger may be implemented in such a way that changes violating data constraints and business rules are not implemented. For instance, if a trigger is set on employee salary, an ‘ignore change’ option sets in when the updated salary hasn’t exceeded the salary limit of employees within the corporation.

3. Logging Changes

For instance, in case for example the salary of a customer changes, salary records may be altered. A trigger logs all the updated changes to an audit table within a database. This feature is important for either searching through old changes or data problems.

4. Disallowing Formation of Deletions

Some records in a database may be relevant or used as reference records by other records. Therefore such records may be declared critical and therefore, they may not be deleted ever. Triggers can be implemented in a way that some rows are protected from deletion by the end user.