为什么这两个sql的结果不同

Question

我尝试使用以下查询更新表中的列。在那种情况下，更新32000行。

Update Table72D012 t2 set DEFINING_ARGUMENT_ID = 
(
SELECT t3.ID 
FROM  Table70t3 t3, 
     Table70t1 t1, 
     Table70t0 t0,   
     Table4 t4 
WHERE t2.Model_id = t4.ID 
AND  t3.ID = t1.PARAM_VALUE_BPVA_ID 
AND  t3.VALUE_BPAR_ID = t0.ID 
AND  t0.KEY='SPECIAL_KEY' 
AND  t1.LANGUAGE='en' 
AND  t4.Model = t1.name 

); 

我想检查结果，我用下面的查询来获得相关ID的计数。我得到了26500结果..为什么结果（更新计数和选择结果计数）彼此不同？
我该如何纠正UPDATE查询？

只能选择

SELECT t3.ID 
FROM  Table70t3 t3, 
     Table70t1 t1, 
     Table70t0 t0, 
     Table72D012 t2, 
     Table4 t4 
WHERE t2.Model_id = t4.ID 
AND  t3.ID = t1.PARAM_VALUE_BPVA_ID 
AND  t3.VALUE_BPAR_ID = t0.ID 
AND  t0.KEY='SPECIAL_KEY' 
AND  t1.LANGUAGE='en' 
AND  t4.Model = t1.name 

Answer 1

首先，你需要了解正确的联接语法。在WHERE子句中进行连接是一个糟糕的主意。

原因很简单。第一个查询是在表中更新非常行，因为您没有WHERE子句或其他条件。

第二个查询返回与查询匹配的所有行。在更新版本中，这些行将获得NULL值。

这是很好的语法，通过MS SQL，但不支持DB2：

Update Table72D012 t2 
    set DEFINING_ARGUMENT_ID = t3.ID 
    from (SELECT t4.id as t4_id, t3.ID 
      FROM Table70t3 t3 join 
       Table70t1 t1 
       on t3.ID = t1.PARAM_VALUE_BPVA_ID join 
       Table70t0 t0 
       on t3.VALUE_BPAR_ID = t0.ID join 
       Table4 t4 
       on t4.Model = t1.name 
      WHERE t0.KEY='SPECIAL_KEY' AND t1.LANGUAGE='en' 
     ) t 
    WHERE t2.Model_id = t4_ID 

我不认为DB2允许在一个UPDATE子句，所以你需要的东西是这样的：

Update Table72D012 t2 
    set DEFINING_ARGUMENT_ID = 
     (SELECT t3.ID 
      FROM Table70t3 t3 join 
       Table70t1 t1 
       on t3.ID = t1.PARAM_VALUE_BPVA_ID join 
       Table70t0 t0 
       on t3.VALUE_BPAR_ID = t0.ID join 
       Table4 t4 
       on t4.Model = t1.name 
      WHERE t0.KEY='SPECIAL_KEY' AND t1.LANGUAGE='en' and t2.Model_id = t4.ID 
     ) 
    WHERE exists    
     (SELECT t3.ID 
      FROM Table70t3 t3 join 
       Table70t1 t1 
       on t3.ID = t1.PARAM_VALUE_BPVA_ID join 
       Table70t0 t0 
       on t3.VALUE_BPAR_ID = t0.ID join 
       Table4 t4 
       on t4.Model = t1.name 
      WHERE t0.KEY='SPECIAL_KEY' AND t1.LANGUAGE='en' and t2.Model_id = t4.ID 
     )