MySQL:The used SELECT statements have a different number of columns

执行SQL报错:The used SELECT statements have a different number of columns 以上翻译:使用的SELECT语句具有不同数量的列 原因:我们在 SQL 语句中使用了 UNION 连接两张表时,查询字段数量不一致导致 # 效果展示: 我们需要将数据展示如上图所示 # 错误案例: SELECT a.quantity AS in_quantity, a.price AS in_price, (a.quantity * a.price) AS in_amount, 0 AS out_quantity, 0 AS out_price