mysql鏈接

inner join
from table_a a inner join table_b b on a.xxx = b.xxx
left join
左鏈接會讀取左表中的數據，即便右邊中沒有數據
from table_a a left join table_b b on a.xxx = b.xxx
right join
右鏈接會讀取右表中的數據，即便左表中沒有數據
from table_a a right join table_b b on a.xxx = b.xxx