Database Basics (variables, operators, if statements, while statements)

Variable:

Define variable: DECLARE @ variable name data type
Variable assignment: SET @ variable name = value
Output: Print variable or string

The SQL language, like other programming languages, has control statements such as variables, branches, loops, and so on.

In SQL language, variables are divided into local variables and global variables, and global variables are called system variables.

Local variables:

Using the declare keyword to declare a variable, the syntax is simple: DECLARE @< variable name > < variable type >

You can assign values to variables using the set keyword, and you can assign only one value to a variable at a time using the Set keyword.

We can also assign a value to this variable in a query statement.

Example:

Global variables: Also called system variables.

Examples of several system variables that are commonly used:

Variable Small exercise:

You need to print a single quotation mark in a printed string: Double-two single quotes.

Operator:

Practice:

Operator Precedence:

If ... else ... Statement:

If ... else usage, if there is no parenthesis, curly braces are replaced with begin end

If judging condition
Begin
The statement to execute
End
Else
Begin
The statement to execute
End

Example:

Practice:

While statement:

Example:

While if nested example:

Example of break in while:

Example of parsing each step of a loop print:

Database Basics (variables, operators, if statements, while statements)