select * from 表名

where A in ('') or a is null

----------

通用SQL

SELECT * FROM 表名  WHERE 1=1 ${IF(参数名)==0,""," and (case when a is null then '' else a end) in ('"+参数名+"')"}

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控件数据集

SELECT (case when a='' or a is null then '空' else a end) [new_] FROM TABLE

查询SQL

SELECT * FROM 表名  WHERE 1=1 ${IF(参数名)==0,""," and (case when a is null then '' else a end) in ('"+REPLACE(参数名,"空","''")+"')"}

select * from 表名

where1=1

${if(len(a)=0,"","and A='"+a+"'")}

select * from 表名

where A in ('') or a is null

或

select * from 表名

where A = '${控件}'