子报告中使用的查询

Question

Select 
    * 
From  
    EmploymentDetails a 
Left Join 
    PersonalInfo b 
On 
    a.cnic = b.cnic 
Left Join 
    Warning c 
On 
    a.cnic = c.cnic
Where 
    a.cnic = '{?cnic}' 

此查询显示结果4次。如何解决每个cnic只显示一次结果？