SELECT *from t_distribution;
SELECT *from t_department;
SELECT t_distribution.ad_area_code,t_distribution.area_num,t_department.ad_area_name
FROM t_distribution
LEFT JOIN t_department
ON t_distribution.ad_area_code =t_department.ad_area_id;
SELECT A.ad_area_code,A.area_num,A.flag,t_department.ad_area_name
FROM t_distribution as A
RIGHT JOIN t_department
ON A.ad_area_code =t_department.ad_area_id;
SELECT t_distribution.area_num,t_distribution.ad_area_code,t_department.ad_area_name
FROM t_distribution
INNER JOIN t_department
ON t_distribution.ad_area_code =t_department.ad_area_id
结果2：
结果3：
结果4：
结果5：
