How to use If Then Else in a MySQL update query?

Question

I want to update a table in MySQL like this:

UPDATE Table
SET A = \'20\' IF A > 20
SET A = A    IF A < 20 
SET A = 0    IF A <= 1
WHERE A IS NOT NULL;
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Answer 1

UPDATE Table
SET A = Case
When A > 20 Then 20 
When A <= 1 Then 0
End
WHERE A IS NOT NULL and ( A > 20 or A <= 1 )

or more simply, 2 statements

UPDATE Table
SET A = 20 
where A > 20;

UPDATE Table
SET A = 0
where A <= 1;