我需要比较两个表中的数据并在新表中显示它们

Question

我需要比较两个表（tbl1和tbl2）中的数据，并在新表（tbl_new）中显示它们。

tbl01

------------------------------
price     mat_group     major
------------------------------
100       a001          a
200       a002          a
450       a003          a
520       b001          b
250       b002          b
170       c001          c
80        c002          c

tbl02

------------------------------
price     mat_group     major
------------------------------
150       a001          a
180       a002          a
320       a003          a
220       b001          b
350       b002          b
520       c003          c

tbl_new

---------------------------------------------
t1.price     t2.price     mat_group     major
---------------------------------------------
100          150          a001          a
200          180          a002          a
450          320          a003          a
520          220          b001          b
250          350          b002          b
170                       c001          c     
80                        c002          c  
             520          c003          c

请给我一些MySQL语法？

Answer 1

使用 LEFT JOIN 的组合。首先使用唯一mat_group值的子查询连接第一个表，然后将其与第二个表连接。

<强>查询

select 
  `t`.`price_1`, 
  `t`.`price_2`, 
  coalesce(`t`.`mat_group_1`, `t`.`mat_group_2`) as `mat_group`, 
  coalesce(`t`.`major_1`, `t`.`major_2`) as `major`
from(
  select 
    `t1`.`price` as `price_1`, 
    `t1`.`mat_group` as `mat_group_1`, 
    `t1`.`major` as `major_1`,
    `t2`.`price` as `price_2`, 
    `t2`.`mat_group` as `mat_group_2`, 
    `t2`.`major` as `major_2` 
  from(
    select `mat_group` from `tbl01`
    union
    select `mat_group` from `tbl02`
  ) as `mg` 
  left join `tbl01` as `t1`
  on `t1`.`mat_group` = `mg`.`mat_group` 
  left join `tbl02` as `t2`
  on `t2`.`mat_group` = `mg`.`mat_group`
) as `t`;

<强> Find a fiddle demo here