列相等与不等

最新推荐文章于 2024-09-16 09:14:14 发布

转载最新推荐文章于 2024-09-16 09:14:14 发布 · 78 阅读

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CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/hilite/archive/2010/01/23/1654967.html

本文介绍了一种在SQL中处理NULL值的方法，通过比较不同情况下的变量值来判断是否相等，有效避免了因NULL值导致的逻辑运算错误。

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declare @f1 int, @v1 int
set @f1=null
set @v1=null
if @f1=@v1 or (@f1 is null and @v1 is null) print '相同' else print '不同'
if @f1<>@v1 or (@f1 is null and @v1 is not null) or (@f1 is not null and @v1 is null)
print '不同' else print '相同'

print '------------------------------------------'
set @f1=1
set @v1=1
if @f1=@v1 or (@f1 is null and @v1 is null) print '相同' else print '不同'
if @f1<>@v1 or (@f1 is null and @v1 is not null) or (@f1 is not null and @v1 is null)
print '不同' else print '相同'

print '------------------------------------------'
set @f1=1
set @v1=null
if @f1=@v1 or (@f1 is null and @v1 is null) print '相同' else print '不同'
if @f1<>@v1 or (@f1 is null and @v1 is not null) or (@f1 is not null and @v1 is null)
print '不同' else print '相同'

print '------------------------------------------'
set @f1=null
set @v1=1
if @f1=@v1 or (@f1 is null and @v1 is null) print '相同' else print '不同'
if @f1<>@v1 or (@f1 is null and @v1 is not null) or (@f1 is not null and @v1 is null)
print '不同' else print '相同'

print '------------------------------------------'
set @f1=0
set @v1=1
if @f1=@v1 or (@f1 is null and @v1 is null) print '相同' else print '不同'
if @f1<>@v1 or (@f1 is null and @v1 is not null) or (@f1 is not null and @v1 is null)
print '不同' else print '相同'

print '------------------------------------------'

解决由于Null致使逻辑运算产生的误差

转载于:https://www.cnblogs.com/hilite/archive/2010/01/23/1654967.html