Left Join multiple tables on a parent table and subtract one column from the parent table

Question

我有 3 个 table（donor_detail、items 和 store）加入了 1 个父 table（donated_items), 现在父级 table 中有一列 quantity 我想从另一个 table 的列中减去，即 issued_donation.issued_quantity 这是我的 SQL 左连接但我不明白我应该如何减去该列。即 donated_items.quantity - issued_donation.issued_quantity

SELECT t1.*, t2.donor_name,t2.ID, t3.ID,t3.item_name, t4.store_name, t4.ID
FROM donated_items as t1
LEFT JOIN donor_detail  as t2 ON t1.donor_id = t2.ID
LEFT JOIN items  as t3 ON t1.item_id = t3.ID
LEFT JOIN stores  as t4 ON t1.store_id = t4.ID

Answer 1

你的问题不是很清楚，但我怀疑你是在谈论减去值，而不是列。如果我是对的，您必须加入其他 table (issued_donation)，然后您可以向所选字段添加类似 t1.quantity - t5.issued_quantity AS remainingQuantity.

的内容

Left Join multiple tables on a parent table and subtract one column from the parent table

Left Join multiple tables on a parent table and subtract one column from the parent table

sql-server

join

subtraction