SELECT 
 Date, T1_Client_name, T1_details, T1_Target, T2_Achieve     
 FROM 
    (SELECT  
          target.target_date as Date, target.target_id, target.customer_name as T1_Client_name, target.target_product as T1_details, target.target_pay as T1_Target, NULL AS T2_Achieve
     FROM 
         target_value AS target 
        
         UNION ALL
     SELECT
      order_item.order_id, NULL as T1_Client_name, NULL AS details,  NULL as T1_Target, quantity AS T2_Achieve
              FROM 
         order_item) AS order_item
      LEFT JOIN
    ( SELECT  
          NULL AS Date, orders.order_id, orders.client_name, NULL as T1_Client_name, NULL AS details,  NULL as T1_Target, NULL AS T2_Achieve
     FROM 
         orders) AS orders ON orders.order_id = order_item.order_id
    LEFT JOIN 
        (SELECT 
             customer.customer_id,  customer.customer_name 
         FROM 
             customer) AS customer ON customer.customer_id = orders.client_name     
   ORDER BY 
    Date ASC ;   

MySQL said: Documentation

#1222 – The used SELECT statements have a different number of columns

please tell me my about my mistake ?