mysql查询是否有可能返回true / false而不是值？

Question

我有一张桌子：

custID    orderID    orderComponent
=====================================
1          123        pizza
1          123        wings
1          234        breadsticks
1          239        salad
2          456        pizza
2          890        salad

我有一个价值清单 - 比萨饼，翅膀，面包棒和沙拉。 如果客户至少有一条包含其中每条记录的记录，我需要一种方法来获得真/假值。 这是可能的mysql查询，或者我只需要为每个用户做一个select distinct(orderComponent)并使用php检查结果？

Answer 1

如果您只是想查看客户是否订购了所有商品，那么您可以使用：

select t1.custid,
  case when t2.total is not null 
    then 'true'
    else 'false'
  end OrderedAll
from yourtable t1
left join
(
  select custid, count(distinct orderComponent) Total
  from yourtable
  where orderComponent in ('pizza', 'wings', 'breadsticks', 'salad')
  group by custid
  having count(distinct orderComponent) = 4
) t2
  on t1.custid = t2.custid

请参阅SQL Fiddle with Demo

如果你想扩展它，看看custid是否订购了单个订单中的所有商品，那么你可以使用：

select t1.custid,
  t1.orderid,
  case when t2.total is not null 
    then 'true'
    else 'false'
  end OrderedAll
from yourtable t1
left join
(
  select custid, orderid, count(distinct orderComponent) Total
  from yourtable
  where orderComponent in ('pizza', 'wings', 'breadsticks', 'salad')
  group by custid, orderID
  having count(distinct orderComponent) = 4
) t2
  on t1.custid = t2.custid
  and t1.orderId = t2.orderid

请参阅SQL Fiddle with Demo

如果您只想要custid和true / false值，那么您可以为查询添加distinct 。

select distinct t1.custid,
  case when t2.total is not null 
    then 'true'
    else 'false'
  end OrderedAll
from yourtable t1
left join
(
  select custid, count(distinct orderComponent) Total
  from yourtable
  where orderComponent in ('pizza', 'wings', 'breadsticks', 'salad')
  group by custid
  having count(distinct orderComponent) = 4
) t2
  on t1.custid = t2.custid

请参阅SQL Fiddle with Demo

或者通过custid和orderid：

select distinct 
  t1.custid,
  t1.orderid,
  case when t2.total is not null 
    then 'true'
    else 'false'
  end OrderedAll
from yourtable t1
left join
(
  select custid, orderid, count(distinct orderComponent) Total
  from yourtable
  where orderComponent in ('pizza', 'wings', 'breadsticks', 'salad')
  group by custid, orderID
  having count(distinct orderComponent) = 4
) t2
  on t1.custid = t2.custid
  and t1.orderId = t2.orderid

请参阅SQL Fiddle with Demo

Answer 2

select case when 
count(distinct orderComponent) = 4 
then 'true' 
else 'false' 
end as bool
from tbl
where custID=1

Answer 3

这是一种方法。 此方法不需要内联视图（派生表），如果要包含多个条件的标志，则此方法可能有效：

编辑：

这将返回包含所有四个项的行的custID ：

SELECT t.custID
     , MAX(IF(t.orderComponent='breadsticks',1,0))
       + MAX(IF(t.orderComponent='pizza',1,0))
       + MAX(IF(t.orderComponent='salad',1,0))
       + MAX(IF(t.orderComponent='wings',1,0)) AS has_all_four
  FROM mytable t
 GROUP BY t.custID
HAVING has_all_four = 4

---

原始答案：

（这检查了具有所有四个项目的客户“订单”，而不仅仅是“custID”。）

SELECT t.custID
     , t.orderID
     , MAX(IF(t.orderComponent='breadsticks',1,0))
       + MAX(IF(t.orderComponent='pizza',1,0))
       + MAX(IF(t.orderComponent='salad',1,0))
       + MAX(IF(t.orderComponent='wings',1,0)) AS has_all_four
  -- , MAX(IF(t.orderComponent='breadsticks',1,0)) AS has_breadsticks
  -- , MAX(IF(t.orderComponent='pizza',1,0)) AS has_pizza
  -- , MAX(IF(t.orderComponent='salad',1,0)) AS has_salad
  -- , MAX(IF(t.orderComponent='wings',1,0)) AS has_wings
  FROM mytable t
 GROUP BY t.custID, t.orderID
HAVING has_all_four = 4

这将得到包含所有四个项目的“订单”。 如果只想返回custID的值，则使用上面的查询作为内联视图（将其包装在另一个查询中）

SELECT s.custID
  FROM (
         SELECT t.custID
              , t.orderID
              , MAX(IF(t.orderComponent='breadsticks',1,0))
                + MAX(IF(t.orderComponent='pizza',1,0))
                + MAX(IF(t.orderComponent='salad',1,0))
                + MAX(IF(t.orderComponent='wings',1,0)) AS has_all_four
             FROM mytable t
            GROUP BY t.custID, t.orderID
           HAVING has_all_four = 4
       ) s
 GROUP BY s.custID

Answer 4

@EmmyS：你可以两种方式做到。 如果要使用MySql检查，请使用：

SELECT @rowcount:=COUNT(*) FROM orderComponent Where (Your Conditions);
IF (@rowcount > 0) THEN
    'True'
ELSE
    'False'
END IF