Question

我正在尝试查找此查询的结果：

SELECT * 
FROM   Table1 
WHERE  ColumnX in (SELECT DISTINCT ColumnX FROM Table2 
                   UNION
                   SELECT DISTINCT ColumnY FROM Table2)

它还使用此查询过滤DateAddedToMarket（Table1中的一列）的结果：

         DateAddedToMarket >= '2018-01-01' 
AND      DateAddedToMarket < '2018-02-01' 
ORDER BY DateAddedToMarket DESC

我试过了：

SELECT * 
FROM   Table1 
WHERE  ColumnX in (SELECT DISTINCT ColumnX FROM Table2 
                   UNION
                   SELECT DISTINCT ColumnY FROM Table2) 
AND    DateAddedToMarket >= '2018-01-01' 
AND    DateAddedToMarket < '2018-02-01' 
ORDER BY DateAddedToMarket DESC

我收到了正确的日期，但也收到了我希望从表2中匹配的值之外的结果。

+--------+--------------+
|ColumnX |    ColumnY   |
+--------+--------------+
| 872510 |       879962 |
| 872514 |       879963 |
| 872511 |              |
| 872515 |              |
| 872512 |              |
| 879529 |              |
| 872513 |              |
| 879530 |              |
| 879959 |              |
| 879960 |              |
| 879961 |              |
+--------+--------------+

Answer 1

如果要在子查询表（在本例中为表2）中搜索DateAddedToMarket，则此查询将不起作用。

在这里，主查询从表1中获取数据。表2中找到了ColumnX.因此日期过滤器（DateAddedToMarket）不适用于此。它只是抓住Table1到ColumnX给它的一切......

实际上，如果您尝试在表2中进行搜索，那么此查询将无法实现此目的。你需要这样做：

SELECT * FROM Table1 WHERE ColumnX in (

SELECT DISTINCT ColumnX FROM Table2 WHERE DateAddedToMarket ... UNION

SELECT DISTINCT ColumnY FROM Table2 WHERE DateAddedToMarket ...)

Answer 2

select子句“IN”函数非常低效，除非查询优化器可以使它成为连接。改变你“in（... union ...）”子句并加入表格。然后在where子句 s 和Union两个几乎相同的选择中添加过滤器。

SELECT Table1.* FROM Table1 
JOIN Table2 on Table1.ColumnX = Table2.ColumnX
where Table1.DateAddedToMarket >= '2018-01-01' 
AND    Table1.DateAddedToMarket < '2018-02-01' 
UNION
SELECT Table1.* FROM Table1 
JOIN Table2 on Table1.ColumnX = Table2.ColumnY
where    Table1.DateAddedToMarket >= '2018-01-01' 
AND    Table1.DateAddedToMarket < '2018-02-01' 
ORDER BY Table1.DateAddedToMarket DESC

如何组合两个查询？

2 个答案: