加入同一张表

Posted 2023-04-19

【中文标题】加入同一张表

【英文标题】：JOIN the same table

【发布时间】：2013-02-20 12:56:50

【问题描述】：

您好，我有表格徽章，其中包含 facility 和 date 列（其他列不重要）。 我想select count(*) 应该是这样的：

DATE       | FACILITY 4 COUNT | FACILITY 1 COUNT
12/12/2012 | 234              |  647

我为facility 1 和 4 编写了两个单独的查询，但是如何将它加入一个查询；

SELECT
    date,
    COUNT(*)
    FROM      badge
    WHERE     facility = 3
    AND       xtype = 19
    AND       date BETWEEN 'some_date' AND 'some_date'
    GROUP BY  date

另一个查询的不同之处仅在于设施的值。

编辑：它是informix 数据库。

【参考方案1】：

SELECT date,
       SUM(case when facility = 1 then 1 else 0 end) "FACILITY 1 COUNT",
       SUM(case when facility = 4 then 1 else 0 end) "FACILITY 4 COUNT"
FROM      badge
WHERE     (facility = 1 OR facility = 4)
AND       xtype = 19
AND       date BETWEEN 'some_date' AND 'some_date'
GROUP BY  date

【讨论】：

我会在 where 子句中添加 AND (facility = 1 OR facility = 4) 以提高查询效率。

【参考方案2】：

试试看，

SELECT  date,
        SUM(CASE WHEN facility = 3 THEN 1 ELSE 0 END) `Facility 3 Count`,
        SUM(CASE WHEN facility = 1 THEN 1 ELSE 0 END) `Facility 1 Count`
FROM      badge
WHERE     xtype = 19 AND      
          date BETWEEN 'some_date' AND 'some_date'
GROUP     BY  date