Question

我不明白为什么我能这样做：

SELECT YEAR(CREATION_TIME) AS y, MONTH(CREATION_TIME) as m, COUNTRY_CODE
FROM PRODUCTS INNER JOIN COMPANIES
ON COMPANIES.COMPANY_KEY = PRODUCTS.CUSTOMER_ID
WHERE CREATED_BY IN ('VOLVO','SAAB')

但不是

SELECT y FROM
(
    SELECT YEAR(CREATION_TIME) AS y, MONTH(CREATION_TIME) AS m, COUNTRY_CODE
    FROM PRODUCTS INNER JOIN COMPANIES
    ON COMPANIES.COMPANY_KEY = PRODUCTS.CUSTOMER_ID
    WHERE CREATED_BY IN ('VOLVO','SAAB')
)

我收到以下错误：

错误：DB2 SQL错误：SQLCODE = -104，SQLSTATE = 42601， SQLERRMC = ;; CORRELATION NAME，DRIVER = 3.53.70 SQLState：42601 ErrorCode：-104错误：DB2 SQL错误：SQLCODE = -514，SQLSTATE = 26501， SQLERRMC = SQL_CURLH200C1，DRIVER = 3.53.70 SQLState：26501 ErrorCode： -514

我的最终目标是做一些事情：

SELECT y, m, COUNTRY_CODE, count(*)
FROM
(
    SELECT YEAR(CREATION_TIME) AS y, MONTH(CREATION_TIME) AS m, COUNTRY_CODE
    FROM PRODUCTS INNER JOIN COMPANIES
    ON COMPANIES.COMPANY_KEY = PRODUCTS.CUSTOMER_ID
    WHERE CREATED_BY IN ('VOLVO','SAAB')
)
GROUP BY y, m, COUNTRY_CODE

Answer 1

第二个查询中的语法不正确。如果不引用该表，则无法引用列别名。这应该有效：

SELECT t.y FROM
(
    SELECT YEAR(CREATION_TIME) AS y, MONTH(CREATION_TIME) AS m, COUNTRY_CODE
    FROM PRODUCTS INNER JOIN COMPANIES
    ON COMPANIES.COMPANY_KEY = PRODUCTS.CUSTOMER_ID
    WHERE CREATED_BY IN ('VOLVO','SAAB')
) AS t

Answer 2

您必须运行一个非常旧的DB2版本。在某些时候，子选择需要相关名称，所以试试这个：

SELECT t.y FROM
(
    SELECT YEAR(CREATION_TIME) AS y, MONTH(CREATION_TIME) AS m, COUNTRY_CODE
    FROM PRODUCTS INNER JOIN COMPANIES
    ON COMPANIES.COMPANY_KEY = PRODUCTS.CUSTOMER_ID
    WHERE CREATED_BY IN ('VOLVO','SAAB')
) AS t

为什么我不能在内心桌上选择？

2 个答案: