数据库常见问题解决汇总

（1）查询某个字段不为空的数据

select * from tb_Grade where GradeName is not null 或 select * from tb_Grade where LEN(GradeName)>0

或

select * from tb_Grade where ISNULL(GradeName,'1')!='1' 或 select * from tb_Grade where not GradeName is null

（2）检测null值

select * from tb_Grade where GradeName is null

（3）查询某个表或视图的所有字段名称

select COLUMN_NAME,DATA_TYPE,IS_NULLABLE,COLUMN_DEFAULT
from INFORMATION_SCHEMA.COLUMNS
where TABLE_NAME='View_KnowledgeCategory_Edubg_Discipline'
order by ORDINAL_POSITION

解析：查询表或视图每个字段的名称，数据类型，是否可以为空，默认值

（4）自定义函数

定义：

USE [EducationCloud]
GO
/****** Object: UserDefinedFunction [dbo].[aaa] Script Date: 2015/3/20 15:59:28 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER function [dbo].[aaa](@a int,@b int,@c int)
returns int as
begin
declare @k int
set @k=0
set @k=@a+@b+@c
return @k
end

执行:select * from tb_Discipline where SpecialtyID=dbo.aaa(5,5,4)

(5)简单使用case when

select
(
case GradeName
when '一年级' THEN '小学'
when '二年级' THEN '小学'
when '三年级' THEN '小学'
when '四年级' THEN '小学'
when '五年级' THEN '小学'
when '六年级' THEN '小学'
when '初一' THEN '初中'
when '初二' THEN '初中'
when '初三' THEN '初中'
when '高一' THEN '高中'
when '高二' THEN '高中'
when '高三' THEN '高中'
else '其他'
end) form tb_Grade