Question

我有桌名＆＃39; employeecount＆＃39;以下数据

month , driver, engineer
January , 100,200
March , 300,400
December , 500,600

我想要以下结果

January , 100,200
February , 0,0
March , 300,400
April , 0,0
May , 0,0
June , 0,0
July , 0,0
August , 0,0
September , 0,0
October , 0,0
November , 0,0
December , 500,600

我尝试过创建月份参考表并进行左外连接。但它有效。

请帮助进行查询。

Answer 1

使用LEFT JOIN尝试此示例查询。

SELECT ref.month, emp.driver, emp.engineer 
FROM referencetable  ref
LEFT JOIN  employeecount emp
ON emp.month = ref.month;

Answer 2

实际上，左连接将完全符合您的预期。尝试使用此查询：

select rm.month,e.driver, e.engineer 
from 
refmonth rm left join employeecount e 
on (e.month=rm.month);

在这里，我将参考月份表格设为refmonth，如下所示：

month
January
February
March
April
May
June
July
August
September
October
November
December

因此，如您所述，查询结果将包含NULL而不是0。

SQL-Select查询到结果所有12个月，即使数据不存在

2 个答案: