select count(*) from T_BookOrder where OrderID in(SELECT DISTINCT OrderID FROM T_BookOrder WHERE (OrderState = '0') AND (UserName = '16120300'))
select count(*) from T_BookOrder where OrderID in(SELECT DISTINCT OrderID FROM T_BookOrder WHERE (OrderState = '0') AND (UserName = '16120300')) 和 select count(order) FROM T_BookOrder 没有区别,得到的结果都是一样的
select count(*) from (SELECT OrderID FROM T_BookOrder WHERE (OrderState = '0') AND (UserName = '16120300') group by OrderID) A
in(SELECT DISTINCT OrderID
FROM T_BookOrder
WHERE (OrderState = '0') AND (UserName = '16120300'))
in(SELECT DISTINCT OrderID
FROM T_BookOrder
WHERE (OrderState = '0') AND (UserName = '16120300'))
和
select count(order)
FROM T_BookOrder
没有区别,得到的结果都是一样的
(SELECT OrderID
FROM T_BookOrder
WHERE (OrderState = '0') AND (UserName = '16120300') group by OrderID) A