Question

这是我的查询，

SELECT top 100
    UPPER(COALESCE(A.DESCR,C.FULL_NAME_ND)) AS DESCR,
    COALESCE(A.STATE, (SELECT TOP 1 STATENAME 
                       FROM M_STATEMASTER 
                       WHERE COUNTRYCODE = B.CODE)) AS STATENAME,
    COALESCE(A.STATECD, (SELECT TOP 1 CODE 
                         FROM M_STATEMASTER 
                         WHERE COUNTRYCODE = B.CODE)) AS STATECD,
    COALESCE(A.COUNTRYCD, B.CODE) AS COUNTRYCODE
FROM 
    M_CITY A
JOIN 
    M_COUNTRYMASTER B ON A.COUNTRYCD = B.CODE
JOIN 
    [GEODATASOURCE-CITIES-FREE] C ON  B.ALPHA2CODE = C.CC_FIPS
WHERE 
    EXISTS (SELECT 1 
            FROM [GEODATASOURCE-CITIES-FREE] Z 
            WHERE B.ALPHA2CODE=Z.CC_FIPS) 
ORDER BY 
    A.CODE

完美正常工作，但是当我试图获得Row_number() over(order by a.code)我多次获得重复列时。

e.g

SELECT top 100
    UPPER(COALESCE(A.DESCR,C.FULL_NAME_ND)) AS DESCR,
    COALESCE(A.STATE, (SELECT TOP 1 STATENAME 
                       FROM M_STATEMASTER 
                       WHERE COUNTRYCODE = B.CODE)) AS STATENAME,
    COALESCE(A.STATECD, (SELECT TOP 1 CODE 
                         FROM M_STATEMASTER 
                         WHERE COUNTRYCODE = B.CODE)) AS STATECD,
    COALESCE(A.COUNTRYCD, B.CODE) AS COUNTRYCODE
    ROW_NUMBER() OVER(ORDER BY A.CODE) AS RN -- i made a change here
FROM 
    M_CITY A
JOIN 
    M_COUNTRYMASTER B ON A.COUNTRYCD = B.CODE
JOIN 
    [GEODATASOURCE-CITIES-FREE] C ON  B.ALPHA2CODE = C.CC_FIPS
WHERE 
    EXISTS (SELECT 1 
            FROM [GEODATASOURCE-CITIES-FREE] Z 
            WHERE B.ALPHA2CODE=Z.CC_FIPS) 
ORDER BY 
    A.CODE
WHERE 
    EXISTS (SELECT 1 
            FROM [GEODATASOURCE-CITIES-FREE] Z 
            WHERE B.ALPHA2CODE = Z.CC_FIPS)

另一次尝试，当我使用ROW_NUMBER() OVER(ORDER BY newid()) AS RN时，它会占用登录时间来执行。

请记住：CODE是表格M_CITY的Pk，而[GEODATASOURCE-CITIES-FREE]表格中没有关键字。

另一件事：关于JOIN（内连接），Join返回匹配的Rows，右边???

例如：

table 1 with 20 rows,
table2 with 30 rows ,
table 3 with 30 rows

如果我在某个键上加入这3个表，那么获得最大行的可能性是20，我是对的吗？

Answer 1

您的第一个查询无效。它似乎只是。原因是您使用的TOP没有ORDER BY，因此会返回100行的任意组。

添加ROW_NUMBER()时，查询计划会发生变化。。。并且结果集的顺序也会改变。我建议你修复原始查询以使用稳定的排序。

Row_Number（）返回重复的行

1 个答案: