Learn SQL triggers and stored procedures in one article!

Table of contents

1. What is SQL

SQL (Structured Query Language) is the abbreviation of Structured Query Language. It is a standardized language used to manage and operate relational databases. SQL is a declarative language that describes operations on the database by writing SQL statements. SQL has the following characteristics:

Data definition: SQL can be used to define database objects, such as creating tables, modifying table structures, creating views, defining indexes, etc.
Data manipulation: SQL can be used to add, delete, modify, and query data in the database, such as inserting data, updating data, deleting data, and querying data.
Data control: SQL provides access control and permission management mechanisms for the database, which can set user access permissions, create users and roles, etc.
Data query: SQL is a powerful tool for retrieving data from the database. It supports complex query operations, including conditional query, sorting, aggregation, etc.
Data integrity: SQL supports defining data integrity constraints, such as primary keys, foreign keys, unique constraints, etc., to ensure data consistency and integrity.

SQL is cross-platform. Almost all relational database management systems (such as MySQL, Oracle, SQL Server, PostgreSQL, etc.) support the SQL language, so the same syntax and operation methods can be used for database management and query.

In short, SQL is a universal database query and management language. It provides rich functions and flexible syntax, allowing developers to easily interact with the database and realize data storage, query and management.

2. What is a trigger?

A trigger is an object in a relational database that is used to automatically perform a series of operations when a specific event associated with a database table occurs (such as an insert, update, or delete operation). Triggers can be defined in the database and associated with specific tables.

When the event associated with the trigger occurs, the trigger will automatically fire and perform the defined operation. Triggers can execute multiple SQL statements, including queries, inserts, updates, and deletes. Triggers are often used to implement functions such as data constraints, maintenance of data integrity, and logging of data changes.

Triggers have the following important characteristics:

Associated with a table: Each trigger is associated with a specific table in the database and is activated when a specified event occurs on that table.
Event triggering: Triggers can be associated with multiple events on the table, including operations such as inserts, updates, and deletes. When the relevant event occurs, the trigger will be automatically triggered and executed.
Automatic execution: Triggers are automatically executed and do not need to be called manually. When relevant events occur, triggers are automatically activated by the database.
Intra-transaction execution: The operation of the trigger is usually executed in the same transaction as the operation on the table to which the trigger is associated. This ensures the consistency and integrity of the database.

Application scenarios for triggers include:

Data constraints: Data validation and restrictions can be implemented in triggers to ensure that specific data constraints are met.
Data integrity: Triggers can be used to maintain data consistency and integrity, such as related table processing before deletion operations.
Logging of data changes: You can use triggers to record the history of data changes, such as recording information about each update or delete operation.

Excessive and complex triggers may increase the burden and complexity of the database, so you need to carefully consider when designing and applying triggers, and use triggers reasonably according to specific needs.

3. What is a stored procedure?

Stored Procedure is a set of predefined SQL statements that are stored in the database and given a name. Stored procedures can be called and executed multiple times, and can accept parameters and return results. Stored procedures are usually used to perform common database operations, such as data query, data insertion, data update, and data deletion.

The definition and code logic of the stored procedure are stored in the database and can be shared and reused by multiple applications, avoiding the need to write the same SQL statement repeatedly. Stored procedures are compiled and optimized in the database, which can improve execution efficiency and reduce network transmission overhead. It is especially suitable for complex queries and frequent data operations.

Stored procedures can be permission controlled through the security mechanism of the database. Only users with execution permissions can call stored procedures, which improves data security. Stored procedures can contain multiple SQL statements and are executed in one transaction, ensuring data consistency and integrity. Stored procedures are executed in the database, which can reduce the amount of data transmitted over the network and improve system performance. The execution of the stored procedure is completed on the database side. The client program only needs to call the name of the stored procedure and pass parameters, which can reduce the burden of the client program.

The application scenarios of stored procedures include that stored procedures can contain complex query statements and perform operations such as filtering, sorting, and grouping of data. Stored procedures can process and convert data, such as data format conversion, data merging and splitting, and other operations. Stored procedures can be used for data constraints and verification to ensure the legality and integrity of data. Stored procedures can automate data operations, such as regularly performing operations such as data backup, data cleaning, and data updates. In summary, a stored procedure is a reusable block of code that is defined and compiled in a database to perform database operations. By using stored procedures, you can improve system performance, reduce network overhead, simplify client programs, and provide better data security and permission control.