Constants and variables in SQL Server and judgment loop statements

Variables in the database and variables defined in the constant database [Act as a temporary data storage function] --- define variables in the database (run from start to end during runtime, from defining variables to assigning values) -- declare must be added before -- Define the variable: declare @ variable name data type declare @ aavarchar (20) -- assign the value set @ aa

Variables in the database and variables defined in the constant database [Act as a temporary data storage function] --- define variables in the database (run from start to end during runtime, from defining variables to assigning values) -- declare must be added before -- Define the variable: declare @ variable name data type declare @ aa varchar (20) -- assign a value to set @ aa

Database variables and constants

Define variables in the database

[Function of temporary data storage]

--- Define variables in the database (run from start to end during running, from defining variables to assigning values)

-- Declare must be added before

-- Define variable: declare @ variable name Data Type

Declare @ aa varchar (20)

-- Value set @ aa = 'hello'

Set @ aa = 'wusong'

Select * from xuesheng where name = @ aa

-- You can also assign values after select.

Select @ aa = Name from xuesheng where student ID = 10

Applications of variables include:

System constant

-- Returns the number of connections since SQL Server was last started, regardless of whether the connection succeeds or fails.

Print @ connections

-- Returns the error when the previous SQL statement is executed. If the returned result is correct, it indicates that there is an error.

Print @ error

-- Returns the current language.

Print @ language

-- Number of rows affected by the previous sentence (when performing the modification operation, check the number of rows modified)

Print @ rowcount

-- Returns the version information of the database to be installed.

Print @ version

Judgment and loop statements

[In the use of database judgment loop statements, there is no braces used, instead of begin end, the code block is written between begin end]

For example:

Basic If statement format

Basic While statement format

Example: Accumulate and sum