FROM子句中的临时表而不是WITH子句

Question

我有这个查询（运行完美）：

WITH TEMPTABLE AS(
            SELECT count(CONTRACT_ID) AS no_contract, T.BRANCH_ID as branch
            FROM CONTRACT, "EMPLOYMENT" T, TABLE(T."EMPLOYEE") TT
            WHERE CONTRACT.EMPLOYEE_ID = TT.EMPLOYEE_ID
                  AND CONTRACT.CONTRACT_VT_START BETWEEN '01/01/2018' AND '30/06/2018'
            GROUP BY T.BRANCH_ID
        )
        SELECT branch
        FROM TEMPTABLE
        WHERE no_contract IN (SELECT MAX(no_contract)
                             FROM TEMPTABLE);

我想知道是否可以用另一种方式而不是WITH子句来完成。像这样的东西：

SELECT count_per_branch.BRANCH
FROM (SELECT count(CONTRACT_ID) AS no_contract, BRANCH_ID AS BRANCH
      FROM CONTRACT, "EMPLOYMENT" T, TABLE(T."EMPLOYEE") TT
      WHERE CONTRACT.EMPLOYEE_ID = TT.EMPLOYEE_ID
            AND CONTRACT.CONTRACT_VT_START BETWEEN '01/01/2018' AND '30/06/2018'
      GROUP BY T.BRANCH_ID) count_per_branch
WHERE count_per_branch.no_contract =
            (SELECT max(count_per_branch.no_contract)
             FROM count_per_branch);

这给出了ORA-00942：“表或视图不存在”错误在行：9

Answer 1

您可以在FROM子句中使用子查询：

FROM (SELECT count(CONTRACT_ID) ... )

你可以给它一个别名：

FROM (SELECT count(CONTRACT_ID) ... ) count_per_branch

您可以使用该别名来限定列引用：

WHERE count_per_branch.no_contract =

但是您不能将该别名用作另一个子查询中的行源，这是您在此处尝试执行的操作：

(SELECT max(count_per_branch.no_contract)
 FROM count_per_branch)

要以这种方式“重用”子查询，必须使用公用表表达式语法 - 即WITH子句。