Question

我有两张桌子。我想从第一张表中选择1条记录条件在第二个表（active = 0）

中为真

表主管：

    -------------
    | id | name |
    -------------
    | 1  | abc1 |
    | 2  | abc2 |
    | 3  | abc3 |
    | 4  | abc4 |
    | 5  | abc5 |
    -------------

表LeadsDetails：

    -------------------------
    | id | lead_id | active |
    -------------------------
    | 1  | 1       | 1       |
    | 2  | 1       | 0       |
    | 3  | 2       | 0       |
    | 4  | 3       | 1       |
    | 5  | 4       | 0       |
    | 6  | 5       | 0       |
    | 7  | 5       | 0       |
    --------------------------

预期产出：

    --------------
    | id | name   |
    --------------
    | 2  | abc2   |
    | 4  | abc4   |
    | 5  | abc5   |
    --------------

SELECT `Lead`.`id`, `Lead`.`name`, `Lead`.`unsubscribe` 
FROM `leads` AS `Lead` inner JOIN `LeadsDetails` AS `LeadsDetails` 
ON (`LeadsDetails`.`lead_id` = `Lead`.`id`) 
WHERE `LeadsDetails`.`active` = 0

Answer 1

这应该比不存在更快地运行，因为子查询不会为每一行运行;在这种情况下，对于给定的ID，我计算表leaddetails上的活动字段值不为0的情况的数量，并且仅显示该计数为0的行（即，对于给定的id，活动字段始终为0 ）

select l.id, l.name
  from lead l
  join leadsdetails ld
    on l.id = ld.lead_id
 group by l.id, l.name
having sum(case when ld.active <> 0 then 1 else 0 end) = 0

小提琴： http://www.sqlfiddle.com/#!2/00970/2/0

Answer 2

因为只有在活动列没有1时才需要获取记录使用NOT EXISTS

SQL FIDDLE DEMO：http://www.sqlfiddle.com/#!2/00970/1

SELECT * FROM
Lead L
WHERE NOT EXISTS (
  SELECT 1 FROM LeasdDetails LD
  where L.id = LD.lead_id
  AND LD.active =1
)

Answer 3

我认为你可以用exists子句做你想做的事：

select l.*
from Lead l
where exists (select 1 from LeadsDetails ld where ld.lead_id = l.id and ld.active = 0)

如果第二个表中的条件为真，则从第一个表中选择1个记录（所有引用行active = 0）

3 个答案: