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Sql statement case when usage

When we need to determine the meaning of the data display representation directly from the data source, we can use the function Case When in the SQL statement.

Case comes in two formats. Simple Case function and Case search function.

The first format: simple Case function:

Format description

Case column name

When condition value 1 then option 1

When condition value 2 then option 2.

Else default value end

Select case job_level when'1 'then' 1111 'when' 2 'then' 1111 'when' 3 'then' 1111 'else' eee' end from dbo.employee

The second format: Case search function

Format description

Case

When column name = condition value 1 then option 1

When column name = condition value 2 then option 2.

Else default value end

Eg: update employee set e_wage = case when job_level ='1' then e_wage*1.97 when job_level ='2' then e_wage*1.07 when job_level ='3' then e_wage*1.06 else e_wage*1.05 end

Tip: usually when we write Case When statements, it is easy to forget the end of end, be sure to remember yo!

Comparison: the two formats can achieve the same function.

The writing of the simple Case function is relatively simple, but compared with the Case search function, there are some functional limitations, such as writing judgment. One more thing to note is that the Case function only returns the first qualified value, and the rest of the Case will be automatically ignored.

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