SQL - 选择+ MAx（）

Question

我想从销售文件中组合销售人员列表与销售人员上次销售日期。 请注意，销售员可能还没有做任何销售！

SELECT 
    SLSNO, 
    SLSNAME 
FROM 
    SALESMEN 

SELECT 
    SLSNO, 
    max(SALEDATE) 
FROM 
    SALESHEADER 
WHERE 
    SALESMANNO = SLSNO 
GROUP BY 
    SLSNO 
ORDER BY 
    SLSNO 

使用ibm db2。如果可能的话，更喜欢标准的ANSI SQL。

Answer 1

在第二种情况下，如果Latest Sale尚未进行销售，它将为NULL。

-- if you want all salesmen who have made a sale 
SELECT 
    SLSNO, 
    SLSNAME, 
    MAX(SALEDATE) AS [Latest Sale] 
FROM 
    SALESMEN AS s 
JOIN 
    SALESHEADER AS h 
ON 
    h.SLSNO = s.SLSNO 
WHERE 
    SALESMANNO = SLSNO 
GROUP BY 
    SLSNO, 
    SLSNAME 


-- if you want all salesmen even if they don't have a sale 
SELECT 
    SLSNO, 
    SLSNAME, 
    MAX(SALEDATE) AS [Latest Sale] 
FROM 
    SALESMEN AS s 
LEFT OUTER JOIN 
    SALESHEADER AS h 
ON 
    h.SLSNO = s.SLSNO 
WHERE 
    SALESMANNO = SLSNO 
GROUP BY 
    SLSNO, 
    SLSNAME