如何在MySQL中设置的update…中使用case和if语句？

Question

This is what I'm trying to do:

UPDATE
    my_table
SET
    column_a = (
        SELECT
        CASE
            WHEN column_a is null THEN 20
            WHEN column_a < 10 THEN column_a
            WHEN column_a = 10 THEN 20
            ELSE MIN((column_a, 20))
        END
        INTO @var_a
        /* I want to do an if...else now */
        IF(var_a > UNIX_TIMESTAMP(), null, var_a)
    )
WHERE
    column_b = 'something'

How would I do something like this? Thanks!

Answer 1

I think you can use a nested case to do this:

UPDATE
    my_table
SET
    column_a = (
        case
            when (@var_a := (
                case 
                    when column_a is null then 20
                    when column_a < 10 then column_a
                    when column_a = 10 then 20
                    else least(column_a, 20)
                end)) <= unix_timestamp() then @var_a
            else null
        end)
WHERE
    column_b = 'something';

Notice that min() is an aggregate function and you can't use it to get the minimum of the inputs: You need to use least() .

Hope this helps