Database – the difference between various functions of SQL Sever and MySQL

Directory

1. Scalar functions (built-in functions & amp; custom functions)

1. The basic syntax of the scalar function of SQL Server is as follows:

2. The scalar function of MySQL adopts the following syntax:

3. Difference

2. Stored procedure

Third, the difference between stored procedures and scalar functions

4. Partition function (partition table)

5. Trigger

6. Table-valued functions

7. Differences between stored procedures, scalar functions, and table-valued functions in the database


1. Scalar functions (built-in functions & amp; custom functions)

  1. Built-in functions:SQL Server predefines some scalar functions, which can be used directly in SQL queries, such as LEN and LOWER.
  2. User-defined functions:SQL Server allows users to customize scalar functions, which can meet specific needs, such as formatting dates, converting strings to uppercase, and so on.
SQL Server:
SELECT LEN('Hello World') -- built-in function
MySQL:
SELECT length('Hello World'); -- built-in function

1. The basic syntax of the scalar function of SQL Server is as follows:

CREATE FUNCTION function name (@parameter name data type)
RETURNS return value data type
AS
BEGIN
    -- function body
    RETURN return value
END

Among them, @parameter name indicates the parameters of the function, and multiple parameters are separated by commas. RETURNS indicates the return value type of the function. RETURN is used to return the function result.

The following is an example of a SQL Server scalar function that calculates the area of a circle:

CREATE FUNCTION GetCircleArea (@r FLOAT)
RETURNS FLOAT
AS
BEGIN
    DECLARE @PI FLOAT
    SET @PI = 3.14159265358979
    RETURN @PI * @r * @r
END

2. The scalar function of MySQL adopts the following syntax:

CREATE FUNCTION function name (parameter name data type)
RETURNS return value data type
BEGIN
    -- function body
    RETURN return value
END

Similar to the syntax of SQL Server, parameter name represents the parameters of the function, and multiple parameters are separated by commas. RETURNS indicates the return value type of the function. RETURN is used to return the function result.

The following is an example of a MySQL scalar function that calculates the area of a circle:

CREATE FUNCTION GetCircleArea (r FLOAT)
RETURNS FLOAT
BEGIN
    DECLARE PI FLOAT;
    SET PI = 3.14159265358979;
    RETURN PI * r * r;
END

3, difference

The difference between the two is their syntax for creating functions and some details of function syntax.

For example, in SQL Server, the DECLARE statement must precede the BEGIN statement, while in MySQL, you can place the DECLARE statement inside the BEGIN statement. In addition, SQL Server and MySQL will have slightly different data types, function return types, etc.

2. Stored procedure

SQL Server stored procedures are written in the T-SQL language and can accept parameters, execute queries, and return result sets, for example:

CREATE PROCEDURE GetProducts
    @name nvarchar(50)
AS
BEGIN
    SET NOCOUNT ON;
    SELECT * FROM Products WHERE ProductName LIKE '%' + @name + '%';
END;

The above stored procedure accepts a parameter @name, and queries the records in the Products table according to the parameter, and returns the query result.

MySQL stored procedures are written in SQL statements and flow control statements, such as:

DELIMITER $$

CREATE PROCEDURE GetCustomers(IN country VARCHAR(50))
BEGIN
    SELECT * FROM Customers WHERE Country = country;
END $$

DELIMITER;

The above stored procedure accepts a parameter country, queries the records in the Customers table according to the parameter, and returns the query result.

Differences between SQL Server and MySQL stored procedures:

  1. Grammatical differences. SQL Server stored procedures are written in T-SQL, and MySQL stored procedures use SQL statements and flow control statements.
  2. Data type differences. SQL Server stored procedures support more data types, such as .NET data types.
  3. Stored procedure call method. The calling method of MySQL stored procedure is relatively simple, you only need to use CALL stored procedure name to call, while SQL Server needs to use EXECUTE stored procedure name or stored procedure name parameter name=parameter value to call.
  4. Error handling differences. MySQL stored procedures use the SIGNAL statement to throw exceptions, while SQL Server uses the RAISERROR statement.

In short, although there are differences in syntax, the purpose of both is the same, both to improve the performance and security of the database.

3. The difference between stored procedures and scalar functions

Stored procedures and scalar functions are user-defined database objects.

A stored procedure is a collection of SQL statements that are written, compiled, and stored in the database, allowing a set of application logic to be processed and stored on the database server as a single object. Stored procedures can contain control flow statements and data manipulation statements, allowing all users to access and operate the database according to the same logic. Stored procedures typically return values or output parameters and are primarily used to perform transactional and batch operations.

A scalar function is a function that returns only a single value, takes a set of input parameters, calculates a result based on the input parameters, and returns the calculated result value. Scalar functions allow users to customize some reusable calculation logic and save this logic in the function. Scalar functions can call other functions or use other database objects such as tables, views, stored procedures, etc.

In general, the difference between stored procedures and scalar functions is:

A stored procedure is a collection of SQL statements, mainly used to perform transaction processing and batch operations;

A scalar function, on the other hand, is a function that returns only a single value and is mainly used for computation and query operations.

Stored procedures are usually more complex than scalar functions, often involving multiple tables and transaction management, while scalar functions usually only contain simple calculations and have better performance and reusability.

4. Partition function (partition table)

Both SQL Server and MySQL support partitioned tables, but the partition functions are written differently.

In SQL Server, partition functions can be implemented by creating partition schemes and partition functions. When creating a partition scheme, you need to specify a partition function, for example:

CREATE PARTITION FUNCTION my_partition_function (int)
AS RANGE LEFT FOR VALUES (100, 200, 300)

Create partition function my_partition(int)
As range left for values(100,200,300)

This statement creates a partition function named “my_partition_function” , which partitions the table by columns of type int, and the left boundary of each partition is< strong> 0, 100, 200 and 300.

In MySQL, the partition function can be implemented by using the PARTITION BY clause when creating a partitioned table. For example:

CREATE TABLE my_partition_table (
    id INT,
    name VARCHAR(50),
    created_date DATE
)
PARTITION BY RANGE (YEAR(created_date)) (
    PARTITION p0 VALUES LESS THAN (2020),
    PARTITION p1 VALUES LESS THAN (2021),
    PARTITION p2 VALUES LESS THAN (2022),
    PARTITION p3 VALUES LESS THAN MAXVALUE
);

This statement creates a partitioned table named “my_partition_table”, which partitions the table by the year of the created_date column into 4 partitions, each with a right boundary of 2019, 2020, 2021 and the maximum value.

The difference between the two lies in the syntax. The partition function of SQL Server can specify more complex partition logic, such as partitioning according to the modulus of a column of a certain numeric type; while the partition function of MySQL is relatively simple, and can only be partitioned according to the value of a certain column. Values are partitioned.

5. Trigger

How to write SQL Server triggers:

Triggers are used to capture and process data changes in tables. Create a trigger using the CREATE TRIGGER statement.

Create a simple SQL Server trigger example:

CREATE TRIGGER myTrigger
ON myTable
FOR INSERT, UPDATE
AS
BEGIN
    PRINT 'Trigger fired.'
    -- write other code logic here for processing
END

The writing method of MySQL trigger:

MySQL triggers are written slightly differently from SQL Server. MySQL uses the CREATE TRIGGER statement to define a trigger. Most of the elements in the CREATE TRIGGER statement are the same as those in the SQL Server trigger, however, the MySQL trigger also supports the “BODIES” statement block, making it more flexible.

Here is an example of creating a new MySQL trigger:

CREATE TRIGGER myTrigger
AFTER INSERT ON myTable
FOR EACH ROW
BEGIN
    -- write code logic here to process
END

The main difference between these two types of triggers is the difference in syntax, so there are not many operational and functional differences between them. However, it is worth mentioning that the implementation methods of the two may be slightly different, so you may need to pay attention to some differences in specific scenarios. For example, triggers in MySQL support old and new row references, but SQL Server does not support them.

6. Table-valued function

Table-valued functions for SQL Server:

A SQL Server table-valued function (Table-Valued Function) is a function that returns a table, which can be used in queries just like other tables and views. Table-valued functions can accept parameters, and the table structure returned usually varies according to the parameters. The syntax for creating a table-valued function is as follows:

CREATE FUNCTION function_name(@parameter1 datatype, @parameter2 datatype)
RETURNS TABLE
AS
RETURN
SELECT...

For example, here’s an example of a table-valued function that returns all members of a department:

CREATE FUNCTION GetDepartmentEmployees (@DepartmentID int)
RETURNS TABLE
AS
RETURN
SELECT * FROM Employees WHERE DepartmentID = @DepartmentID

The way to call this function is:

SELECT * FROM GetDepartmentEmployees(3)

Here @DepartmentID is the parameter of the GetDepartmentEmployees function, which returns all Employees whose DepartmentID is 3.

MySQL’s table-valued functions:

MySQL’s table-valued function (Table-Valued Function) is a user-defined function that returns a virtual table that can be referenced by other queries. MySQL does not directly support table-valued functions, it uses temporary tables to simulate the effect of table-valued functions, as follows:

CREATE TEMPORARY TABLE temp_table AS
SELECT...

After the temporary table is successfully created, JOIN or UNION it with the result of the SELECT statement, and then it can be used in the query. Here is an example of a table-valued function that returns all members of a department:

CREATE TEMPORARY TABLE Department Employees AS
SELECT * FROM Employees WHERE DepartmentID = @DepartmentID

SELECT * FROM DepartmentEmployees

The way to call this function is:

SET @DepartmentID = 3;
CALL GetDepartmentEmployees(@DepartmentID);

The @DepartmentID here is the parameter of the GetDepartmentEmployees function, and the function returns all Employees whose DepartmentID is 3.

the difference:

SQL Server’s table-valued functions work similarly to MySQL’s table-valued functions, but they have some differences:

  1. The syntax is different: SQL Server’s syntax for creating a table-valued function is CREATE FUNCTION, while MySQL uses CREATE TEMPORARY TABLE.
  2. The calling methods are different: SQL Server is called directly through the function name and parameters in the query, while MySQL is called with the CALL syntax that conforms to the SQL specification.
  3. The return type is different: SQL Server’s table-valued functions return tables, while MySQL’s table-valued functions return tables using a temporary table emulation.
  4. The way to pass parameters is different: SQL Server can use parameters like other functions, and MySQL’s table-valued functions need to use CALL syntax to pass parameters.

In conclusion, table-valued functions can greatly simplify the job of writing complex queries.

Although the syntax and usage of each DBMS is different, they can all achieve the same effect.

7. Storage in the database The difference between procedure, scalar function and table-valued function

Stored procedures, scalar functions, and table-valued functions are three common bodies of reusable code in databases

Their main differences are as follows:

  1. Stored Procedure (Stored Procedure): It is a collection of some SQL statements stored in the database, which can be called and executed at any time, and is a package that can be called repeatedly.
  2. Scalar Function (Scalar Function): is an SQL tool that can accept one or more input parameters and return a scalar value (such as a string, a number, etc.) based on these parameters. Scalar functions can be used in the SELECT statement, WHERE clause, and HAVING clause.
  3. Table Valued Function (Table Valued Function): It is an SQL tool that can return a table (similar to a database table). Similar to a scalar function, a table valued function can also accept one or more input parameters. There are two types of table-valued functions: inline table-valued functions and multi-statement table-valued functions. The former returns a set of result rows for a SELECT statement, while the latter returns a result set after performing some operation on a large amount of data.

In general, stored procedures are more complex than scalar functions and table-valued functions, but for some business logic with more complex requirements, the advantages of stored procedures are more obvious; while scalar functions and table-valued functions are very suitable for querying data multiple times in a conventional way (such as data classification, sorting, statistics, etc.), which can greatly improve the efficiency and speed of querying and processing data.