如何交叉连接 sql 中的两个表

Question

所以我需要交叉连接 2 个表，但我无法在不收到错误的情况下找到这样做的方法

ORA-01427: single-row subquery returns more than one row ORA-06512: at "SYS.DBMS_SQL", line 1721

这是我正在使用的代码，但我不知道我的错误来自哪里，我是 sql 的新手，所以感谢您的帮助：

INSERT INTO Valid_Safety (Area, Course_ID, Course_Name, Personnel_Number, ESA_Name, Section_Leader, Valid, Expire_Date)

Select Safety_Map.Area,
       Course_ID,
       Course_Name,
       _ESA.Personnel_Number,
       _ESA.ESA_Name,
       _ESA.Section_Leader,
    (Select
    COUNT(*) Valid
     From
    SAP_Data
    Where Personnel_Number = TX3_ESA.Personnel_Number
    AND Duplicate1 = 'Valid'
    AND Course_Num = Safety_Map.Course_Num) As Valid,
    
     (Select 
     Expire_Date
     From 
      SAP_Data
    Where Personnel_Number = _ESA.Personnel_Number
    AND Duplicate1 = 'Valid'
    AND Course_Num = Safety_Map.Course_Num) As Expire_Date
   
From Safety_Map CROSS JOIN _ESA;

Answer 1

好吧，看起来像 Expire_Date 的子查询，returns 多于一行：

因此解决方案可能因逻辑而异，但这是一种方法：

...
    (
        Select max(Expire_Date)
        From SAP_Data
        Where Personnel_Number = _ESA.Personnel_Number
        AND Duplicate1 = 'Valid'
        AND Course_Num = Safety_Map.Course_Num
    ) As Expire_Date
From Safety_Map CROSS JOIN _ESA;

Answer 2

(Select Expire_Date 从 SAP_Data 其中 Personnel_Number = _ESA.Personnel_Number AND 复制 1 = 'Valid' AND Course_Num = Safety_Map.Course_Num)

返回多行。如果您只需要前 1 行，那么您可以使用 rownum 或仅获取前 10 行

Select Safety_Map.Area,
       Course_ID,
       Course_Name,
       _ESA.Personnel_Number,
       _ESA.ESA_Name,
       _ESA.Section_Leader,
    (Select
    COUNT(*) Valid
     From
    SAP_Data
    Where Personnel_Number = TX3_ESA.Personnel_Number
    AND Duplicate1 = 'Valid'
    AND Course_Num = Safety_Map.Course_Num) As Valid,
    
     (Select 
     Expire_Date
     From 
      SAP_Data
    Where Personnel_Number = _ESA.Personnel_Number
    AND Duplicate1 = 'Valid'
    AND Course_Num = Safety_Map.Course_Num
    and rownum=1 ) As Expire_Date
   
From Safety_Map CROSS JOIN _ESA;

或者您可以使用聚合（max() 或 min()）：

(Select 
     max(Expire_Date)
     From 
      SAP_Data
    Where Personnel_Number = _ESA.Personnel_Number
    AND Duplicate1 = 'Valid'
    AND Course_Num = Safety_Map.Course_Num
    and rownum=1 ) As Expire_Date

如何交叉连接 sql 中的两个表

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