Question

我正在研究一个逻辑，如果LEFT联合字段为null，那么不应该应用Where中的条件。有人可以告诉我如何只用查询来完成它。

我尝试使用IF CASE，但没有帮助，

查询：

SELECT *
FROM tableA ta
LEFT JOIN tableB tb ON tb.id = ta.id_c
WHERE ta.sales = 'Closed'
  AND tb.deleted=0

当 ta.id_c 为空时， AND tb.deleted = 0 的条件不应考虑到帐户。

为什么呢？因为当链接ID中存在空值时，不会为查询选择数据。有帮助吗？提前谢谢。

预期结果：选择表格的列。

实际表格：

表A：

id_c    sales  
   1    Closed 
   2    Closed

tableB的：

   id  deleted 
   1    0

查询后：当前

id_c    sales   id  deleted 
   1    Closed  1   0

预期

id_c    sales   id    deleted 
   1    Closed  1       0
   2    Closed  NULL   NULL

注意：我无法编辑LEFT JOIN条件

Answer 1

鉴于

create table tableA (
  id_c integer,
  sales varchar(255)
);

create table tableB (
  id integer,
  deleted bool
);

insert into tableA values (1, 'Closed'), (2, 'Closed');
insert into tableB values (1, 0);

SELECT *
FROM tableA ta
LEFT JOIN tableB tb ON tb.id = ta.id_c
WHERE
  (ta.sales = 'Closed' AND tb.deleted = 0) OR
  (ta.sales = 'Closed' AND tb.id is null)

或少一点罗嗦

WHERE
  (ta.sales = 'Closed') AND (tb.deleted = 0 OR tb.id is null);

导致

id_c    sales   id  deleted 
1   Closed  1   0
2   Closed  NULL    NULL

mysql where condition基于左连接字段

1 个答案: