| idperson |工作量|活性| IDPM |姓名|姓氏|

| idsupportday |日期| fk_person |

和这个SQL语句：

SELECT person.idperson, person.firstname, person.lastname, person.workload,
       person.active, person.idpm, COUNT(supportday.idsupportday) AS SupportDays,
       MIN(supportday.date) AS FirstDate, MAX(supportday.date) AS LastDate
FROM   person
INNER JOIN supportday 
ON         person.idperson = supportday.fk_person
WHERE      (person.active = 1)
GROUP BY   person.idperson, person.firstname, person.lastname, person.workload,
           person.active, person.idpm

现在如果supportday表为空，我也会收到一个空结果。但我仍然希望结果中有person.active=1的所有人。

我需要改变什么？

感谢您的回答。

Answer 1

将INNER JOIN更改为LEFT OUTER JOIN：

SELECT person.idperson, person.firstname, person.lastname, person.workload,
       person.active, person.idpm, COUNT(supportday.idsupportday) AS SupportDays,
       MIN(supportday.date) AS FirstDate, MAX(supportday.date) AS LastDate
FROM   person
LEFT OUTER JOIN supportday 
ON         person.idperson = supportday.fk_person
WHERE      (person.active = 1)
GROUP BY   person.idperson, person.firstname, person.lastname, person.workload,
           person.active, person.idpm

仅当两者中至少有一行时，内部联接才会返回行与连接条件匹配的表。内连接消除了行与另一个表中的行不匹配。外连接，但是，返回至少一个表或视图中的所有行在FROM子句中提到，只要这些行符合任何WHERE或有搜索条件。从左表中检索所有行使用左外连接引用，以及右表中的所有行在右外连接中引用。

Answer 2

将INNER JOIN更改为LEFT OUTER JOIN

MS SQL sql语句返回空结果

| idperson |工作量|活性| IDPM |姓名|姓氏|

| idsupportday |日期| fk_person |

2 个答案: