sql server 判空查询

SELECT * FROM tableName WHERE columnName IS NOT NULL  --排除空值
 
SELECT * FROM tableName WHERE ISNULL(columnName, '')<>''  --排除空值和空字符
 
SELECT * FROM tableName WHERE columnName<>NULL --需SET ANSI_NULLS ON但即使符合条件也返回零行
 
SELECT * FROM tableName WHERE columnName<>''  --排除空字符