mysql連接

inner join
from table_a a inner join table_b b on a.xxx = b.xxx
left join
左連接會讀取左表中的數據，即使右邊中沒有數據
from table_a a left join table_b b on a.xxx = b.xxx
right join
右連接會讀取右表中的數據，即使左表中沒有數據
from table_a a right join table_b b on a.xxx = b.xxx