tsql - 如何在 SQL Server CE 中连接两个具有不同列的表？

Question

如何在 SQL Server CE 中加入具有不同列的两个表？

我有两张桌子：

表时间表

+-----+----------+------+
+ ID  + Name     + Type +
+-----+----------+------+
+ 1   + A        + 1    +
+ 2   + B        + 1    +
+ 3   + C        + 2    +
+-----+----------+------+

表格说明

+-----+--------------------+
+ ID  + Description        +
+-----+--------------------+
+ 1   + A1 - XXXXX         +
+-----+--------------------+

我想要得到的是这样的表格：

+-----+----------+-----------------+
+ ID  + Name     + Description     +
+-----+----------+-----------------+
+ 1   + A        + A1 - XXXXX      +
+ 2   + B        + -               +
+ 3   + C        + -               +
+-----+----------+-----------------+

当ID不在表上时，该Description列应填写在哪里。-Description

我试过这段代码：

SELECT S.ID, D.Description 
FROM Schedule AS S 
INNER JOIN Description AS D

但结果是：

+-----+----------+-----------------+
+ ID  + Name     + Description     +
+-----+----------+-----------------+
+ 1   + A        + A1 - XXXXX      +
+ 2   + B        + A1 - XXXXX      +
+ 3   + C        + A1 - XXXXX      +
+-----+----------+-----------------+

当我试图给出 ON 子句时：

SELECT S.ID, D.Description 
FROM Schedule AS S 
INNER JOIN Description AS D ON S.ID = D.ID

它只是获取桌子ID上的行，例如：Description

+-----+----------+-----------------+
+ ID  + Name     + Description     +
+-----+----------+-----------------+
+ 1   + A        + A1 - XXXXX      +
+-----+----------+-----------------+

我怎样才能做到这一点？

---

[更新]

我尝试了这段代码，它可以工作：

SELECT  S.ID, S.Name, COALESCE (D.Description, '-') AS Description
FROM Schedule AS S 
LEFT OUTER JOIN Description AS D ON S.ID = D.ID

但是现在，如何在其上添加 WHERE 子句（请参见上表SCHEDULE）？

我试过了：

SELECT  S.ID, S.Name, COALESCE (D.Description, '-') AS Description
FROM Schedule AS S 
LEFT OUTER JOIN Description AS D ON S.ID = D.ID AND S.Type = '1'

但仍然得到整行。

Answer 1

SQL Server CE 中的左外连接

您需要使用键字段IDLEFT OUTER JOIN来连接表Schedule和Description。此外，用于将描述列中的 NULL 值替换为COALESCE-

脚本：

SELECT          S.ID
            ,   S.Name
            ,   COALESCE (D.Description, '-') AS Description
FROM            Schedule AS S 
LEFT OUTER JOIN Description AS D 
ON              S.ID = D.ID

输出：

经测试Microsoft SQL Server CE version 4.0.8482.1

带有 WHERE 子句

您需要在JOINWHERE之后添加子句。如果你打算有一个，它应该在子句之后。ORDER BYWHERE

脚本：

SELECT          S.ID
            ,   S.Name
            ,   COALESCE (D.Description, '-') AS Description
FROM            Schedule    AS S 
LEFT OUTER JOIN Description AS D 
ON              S.ID = D.ID
WHERE           (S.Type = 1)

输出：

经测试Microsoft SQL Server CE version 4.0.8482.1

Answer 2

你需要LEFT OUTER JOIN.

SQLFiddle：http ://sqlfiddle.com/#!3/7dccf/1

询问：

select s.ID, s.Name, Coalesce(d.description,'-') as description
from schedule s 
left outer join description d on d.id = s.id

Answer 3

您需要使用 anOUTER JOIN而不是INNER，并使用IsNullorCoalesce替换NULL值：

SELECT S.ID, Coalesce(D.Description , '-') AS Description
FROM Schedule AS S FULL OUTER JOIN Description AS D
ON S.ID = D.ID

Answer 4

SELECT S.ID, D.Description 
FROM Schedule AS S FULL OUTER JOIN Description AS D
ON S.ID = D.ID

INNER JOIN表示仅选择两个表中都存在的行。
FULL OUTER JOIN表示选择行，只要它们存在于一个表中。

你需要FULL OUTER JOIN...