MySQL stored procedures and common function code analysis

The concept of mysql stored procedure:

A set of SQL code snippets stored in a database that can perform specific tasks (queries and updates).

The concept of mysql function:

A function is a SQL statement that performs a specific function. Functions are divided into built-in functions and user-defined functions (UDF).

The difference between MySQL stored procedures and functions

• Stored procedures can have multiple in, out, and inout parameters, while functions only have input parameter types and cannot have in.
• The functions implemented by stored procedures are more complex; while functions are more single-functional (targeted) and more targeted.
• Stored procedures can return multiple values; stored functions can only return one value.
• Stored procedures are generally executed independently; while stored functions can appear as components of other SQL statements.
• Stored procedures can call stored functions. Functions cannot call stored procedures.

A stored procedure is a set of SQL statements that are compiled and saved in the database to complete a specific function. The idea is to encapsulate and reuse code at the database SQL language level.

Note: in refers to input parameters, out refers to output parameters

Creating custom functions

Syntax format: create function name (parameter type, parameter type...) returns type return expression value;

Note: 1. There can be no or multiple parameters.

2. There must be a return value, and only one.

3. If there is a SQL statement, put it between begin...end.

4. If you don't add deterministic, you will get an error (I don't know how to solve it)

begin...end compound statement

Usually appears in stored procedures, functions, and triggers, which can contain one or more statements, each separated by ;.

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