SQL Server database Logical control statements

the If-else statement in//sql
IF (condition)
BEGIN
Statement 1
Statement 2
... ...
END
ELSE
BEGIN
Statement 1
Statement 2
... ...
END

Example:
IF (@score > 85)
PRINT ' Exam level: ' + ' excellent '
ELSE IF (@score > 70)
PRINT ' Exam level: ' + ' good '
ELSE IF (@score > 60)
PRINT ' Exam level: ' + ' Medium '
ELSE
PRINT ' Exam level: ' + ' difference '

The while statement in SQL
while (condition)
BEGIN
Statement 1
Statement 2
......
Break
END

Example:
DECLARE @n INT--Failed number
while (1 = 1)-Conditions are always set
BEGIN
SELECT @n=count (*) from Result WHERE [email protected] and [email protected] and Studentresult < 60--number of failed statistics
IF (@n > 0)--plus 2 points per person
UPDATE result SET studentresult=studentresult+2 from Result WHERE [email protected] and [email protected] and Studentresul T < 95
ELSE
Break--Exit loop
END

Case-end Multi-Branch statements
Case
When condition 1 then result 1
When condition 2 then result 2
......
else other results
END
Note: Else indicates that all when conditions in a case are not true when the result is returned
If else is omitted and when condition is false, the case statement returns null

Example:
SELECT study number =studentno, score =case
When Studentresult < ' E '
When Studentresult between, and then ' D '
When studentresult between and "C"
When Studentresult between and the then ' B '
ELSE ' A '
END
From Result
INNER JOIN Subject on Result.subjectno=subject.subjectno

SQL Server database Logical control statements