先来一个简单的sum:select sum(qty) as total_qty from inventory_product group by product_id
这样就会统计出所有product的qty.
但是很不幸,我们的系统里面居然有qty为负值。而我只想统计那些正值的qty,加上if function就可以了。 SQL为:select sum(if(qty > 0, qty, 0)) as total_qty from inventory_product group by product_id
意思是如果qty > 0
, 将qty的值累加到total_qty, 否则将0累加到total_qty.
再加强一点:
1 | select |