please look at the image , you will find mysql CASE WHEN executed even condition is false

_skus

sku_id  is_available  is_quantity   quantity 

 13       1            0                NUll

UPDATE _skus SET is_available =CASE WHEN is_quantity = 1 and quantity=0 THEN 0 END where sku_id=13

after mysql statement executed

sku_id  is_available  is_quantity   quantity 

 13       0           0                NUll

is_available updated to 0 even the condition not true