SQL 不同的查询取决于参数？ [复制]

Question

This question already has an answer here:

• How to make this SQL line more efficient? (Case when in Partition By) 2 answers

I have a query that is the same but needs to change a little depending on which parameter. How can I do this?

Something like

CASE WHEN @LocalDetailLevel = 'master' THEN 
BEGIN
...
END
CASE WHEN @LocalDetailLevel = 'size' THEN 
BEGIN
...
END
CASE WHEN @LocalDetailLevel = 'color'
BEGIN
...
END

And then within each begin/end statement is a whole query with select and from and everything. Is that the correct way to do it? Or do I have to use an if statement? If so, what is the syntax for that?

Also, does anyone know how the sql query will optimize for this? Will it optimize just on one of the parameters/queries?

Answer 1

CASE is an expression and thus isn't used to control logical flow.

CASE can be used in any statement or clause that allows a valid expression. For example, you can use CASE in statements such as SELECT, UPDATE, DELETE and SET, and in clauses such as select_list, IN, WHERE, ORDER BY, and HAVING

For your problem, you would use IF .

The syntax is very similar...

IF @LocalDetailLevel = 'master' 
BEGIN
...
END

IF @LocalDetailLevel = 'size'
BEGIN
...
END