select
		dpt.*,
		info.*,
		gd.*,
		mat.*
		from depart as dpt
		left join info_sys as info on dpt.id = info.dept_name
		left join grade as gd on info.id = gd.grade
		left join material as mat on gd.id = mat.material_pro
		where dpt.id = #{id}
		or info.id = #{id}
		or gd.id = #{id}
		or mat.id = #{id}

		<if test="offset != null and limit != null">
			limit ${offset}, ${limit}
		</if>
 

附表的外來鍵是主表的主鍵

將主表的主鍵的id放在前，將附表的外來鍵放在後

中間用等號連結起來

最後邊加上where條件語句

後邊加上if語句