Question

所以，我有一个简单的SQL查询，但似乎有问题（或者我的where-clause写错了），因为如果我选择特定的字段，它就不会返回值（{ {1}}）具有特定值（matflag）。

查询基本上是50，select from table1上有子查询，table2只检查子查询中返回的字段是否存在于where-clause中：

table1

返回此输出：

Select distinct  
    t1.matnum as matnum, t1.matflag as matflag, t1.factory as factory 
from 
    table1 t1, 
    (select matnum from table2 where technical_value = 'XX') t2 
where 
    t1.matnum = t2.matnum and t1.matnum = '60000000';

如果我将+----------+---------+---------+ | MATNUM | MATFLAG | FACTORY | +----------+---------+---------+ | 60000000 | | 001000 | | 60000000 | | 002000 | | 60000000 | | 003000 | | 60000000 | | 004000 | | 60000000 | | 005000 | +----------+---------+---------+添加到and t1.matflag != '50'的末尾，则整个输出会消失。

where-clause

输出：

Select distinct 
    t1.matnum as matnum, t1.matflag as matflag, t1.factory as factory 
from 
    table1 t1, 
    (select matnum from table2 where technical_value = 'XX') t2 
where 
    t1.matnum = t2.matnum 
    and t1.matnum = '60000000' 
    and t1.matflag != '50';

列+----------+---------+---------+ | MATNUM | MATFLAG | FACTORY | +----------+---------+---------+的附加信息：它是一个varchar2（2个字符）列，要么没有填充，要么填充值＆＃39; 50＆＃39;或者价值＆＃39; 10＆＃39;或者＆＃39; 20＆＃39;。现在，如果我将where子句从matflag更改为and t1.matflag != '50'，则输出再次正确：

and t1.matflag is null

所以这会返回此输出：

Select distinct 
    t1.matnum as matnum, t1.matflag as matflag, t1.factory as factory 
from 
    table1 t1, 
    (select matnum from table2 where technical_value = 'XX') t2 
where 
    t1.matnum = t2.matnum 
    and t1.matnum = '60000000' 
    and t1.matflag is null;

<>如何应用但matflag is null不适用？

我们运行Oracle Database 11g 11.2.0.3.0版 - 64位生产。

Answer 1

了解如何使用正确的显式JOIN语法：

Select distinct t1.matnum as matnum, t1.matflag as matflag, t1.factory as factory 
from table1 t1 join
     table2
     on t1.matnum = t2.matnum
where t2.technical_value = 'XX' and t1.matnum = '60000000';

然后了解NULL值及其几乎每次比较失败的方法，包括<>。

你想要的逻辑是：

where t2.technical_value = 'XX' and t1.matnum = '60000000' and
      (matflag <> '50' or matflag is null)

Answer 2

在SQL NULL中表示“未知”值，因此使用它的任何操作都将导致NULL。试试COALESCE(t1.matflag, 0) <> 50 ...

SQL没有返回正确的值

2 个答案: