Oracle 10g 如何在布尔表达式中评估 NULL
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How Oracle 10g evaluates NULL in boolean expressions
提问by Phani Kumar PV
if not (i_ReLaunch = 1 and (dt_enddate is not null))
How this epression will be evaluated in Oracle 10g
when the input value of the i_ReLaunch = nulland the value of the dt_enddateis not null
it is entering the loop.
According to the rules in normal c# and all it should not enter the loop as
it will be as follows with the values.
当 the 的输入值i_ReLaunch = null和 的值dt_enddate不为空时，如何在 Oracle 10g 中评估此 epression 将进入循环。根据普通c#中的规则，它不应该进入循环，因为它的值如下。
If( not(false and (true))
= if not( false)
=if( true)which implies it should enters the loop
If( not(false and (true))
= if not( false)
=if( true)这意味着它应该进入循环
But it is not happening
但它没有发生
Can someone let me know if i am wrong at any place
有人可以让我知道我是否在任何地方错了
采纳答案by zendar
Boolean operations with NULL value in Oracle return UNKNOWN- not true or false. So you have something like this:
Oracle 中具有 NULL 值的布尔运算返回UNKNOWN- 不是 true 或 false。所以你有这样的事情：
If( not(UNKNOWN and (true)) = if not( UNKNOWN) =if( UNKNOWN )
In this case, IFwill treat UNKNOWN as false.
在这种情况下，IF将 UNKNOWN 视为 false。
If i_relaunchcan be null, then you need to use some of NULL handling functions(NVL, NVL2, NULLIF, COALESCE, LNNVL) to be sure that you have correct result.
如果i_relaunch可以为空，那么您需要使用一些空处理函数( NVL, NVL2, NULLIF, COALESCE, LNNVL) 来确保您得到正确的结果。
See these article for more information:
有关更多信息，请参阅这些文章：
- Nulls: Nothing to Worry About
- Fundamentals of PL/SQL. Scroll down to -
Handling Null Values in Comparisons and Conditional Statements
- 空值：没什么好担心的
- PL/SQL 基础。向下滚动到 -
Handling Null Values in Comparisons and Conditional Statements
