你这个得判断

select * from 表 where 1=1 ${if(len(sql("数据连接", "select date from 表 where date = '"+参数+"' " ,1 )) = 0 , "  and date =select max(date) from 表 " , "and date ='"+参数+"'")  }

大概这么个道理

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and 1=1 ${if(len(月份)==0,"",

             if(len(sql("数据连接","select distinct audit_yf from fr_problem_write where audit_yf = '"+月份+"'",1,1)) == 0 ,

             " and audit_yf  = (select max(audit_yf) from fr_problem_write limit 0,1) ",

             " and audit_yf = '"+月份+"'"

             ))}

之前写过个类似的， 是mysql的你参考一下； 月份参数有数据的查询，没有的查询最近月份