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sql - oracle sql结果不一致

问题描述

我有三个完全相同的 sql 查询。但是，其中之一不返回任何结果。我找不到该问题的适当解释。

任何人都可以

--returns one result
   SELECT col1
   FROM table1
   WHERE col1  not IN
   (select x.hesno from (SELECT c1||c2||c3 FROM Table2 S) x) ; 

--returns no result
   SELECT col1
   FROM table1
   WHERE col1  not IN
     (SELECT c1||c2||c3 FROM table2)  ;


--returns one result
   SELECT col1
   FROM Table1
   WHERE NOT EXISTS (
     SELECT 1 FROM table2 WHERE c1||c2||c3 = col1
   );

这是表格说明

Table1
Name   Null? Type          
------ ----- ------------- 
COL1          VARCHAR2(15)  

Table2
Name            Null? Type          
--------------- ----- ------------- 
C1                    VARCHAR2(2)   
C2                    VARCHAR2(3)   
C3                    VARCHAR2(10)

标签： sqloraclesubquery

解决方案

如果子查询在内部返回空值NOT IN ( subquery )，则查询不会返回行。

下面的 SQL 返回12345

With WTH0 AS (
  SELECT '12345' x FROM dual
),
WTH1 AS (
  SELECT '1' c1, '2' c2, '3' c3 FROM dual
)
SELECT X 
FROM WTH0
WHERE X NOT IN (SELECT C1||C2||C3 FROM WTH1);

然而

With WTH0 AS (
  SELECT '12345' x FROM dual
),
WTH1 AS (
  SELECT '1' c1, '2' c2, '3' c3 FROM dual union
  SELECT null c1, null c2, null c3 FROM dual
)
SELECT X 
FROM WTH0
WHERE X NOT IN (SELECT C1||C2||C3 FROM WTH1);

返回空结果集。

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