如何在MYSQl中合並具有兩列相同內容的多個表

Question

我有四個表table_1，table_2，table_3和table_4。 他們四個人都有這樣的列：

table_1: age_grp, gender, height;
table_2: age_grp, gender, weight;
table_3:  age_grp, gender, shoesize;
table_4: age_group, gender, BMI;

我想用列創建一個新表：

age_grp, gender, height, weight, shoesize, BMI

我只希望合並所有表中age_grp and gender相同的列。 任何想法如何做到這一點？

Answer 1

這很容易通過INNER JOIN ：

SELECT table_1.*, table_2.*, table_3.*, table_4.* FROM table_1  
  INNER JOIN table_2 ON table_1.age_grp = table_2.age_grp  
    AND table_1.gender = table_2.gender
  INNER JOIN table_3 ON table_2.age_grp = table_3.age_grp  
    AND table_2.gender = table_3.gender
  INNER JOIN table_4 ON table_3.age_grp = table_4.age_grp  
    AND table_3.gender = table_4.gender

如果您要求所有表中的所有數據在列中具有相同的值，則可以將任何表與任何表JOIN 。

請注意，您不應在實際的生產腳本中使用* ，而應顯式使用列名稱。

Answer 2

您很有可能不會通過單純的比賽獲得想要的結果。 例如，以下將創建您描述的表：

insert into newtable 
    select t1.age_grp, t1.gender, t1.height, t2.weight, t3.shoesize, t4.BMI 
    from table_1 t1 
    inner join table_2 t2 on t1.age_grp = t2.age_grp 
        and t1.gender = t2.gender
    inner join table_3 t3 on t1.age_grp = t3.age_grp 
        and t1.gender = t3.gender
    inner join table_4 t4 on t1.age_grp = t4.age_grp 
        and t1.gender = t4.gender;

問題是，如果任何一項失敗，您將不會獲得任何支持。 您可以考慮使用外部聯接。

Answer 3

盡管此請求已得到答復，但我想為缺少值的情況添加一個答案，例如，僅不為age_grp / gender對給出鞋號。

對於帶有連接的解決方案，您需要MySQL不支持的FULL OUTER JOIN。 而用LEFT和/或RIGHT OUTER JOINs來模仿這一點可能會給多張桌子帶來痛苦。

這是使用UNION ALL和最終聚合的解決方案。

create table mytable as
select age_grp, gender, max(height) as height, max(weight) as weight, max(shoesize) as shoesize, max(bmi) as bmi
from
(
  select age_grp, gender, height, cast(null as unsigned integer) as weight, cast(null as unsigned integer) as shoesize, cast(null as unsigned integer) as bmi from table_1
  union all
  select age_grp, gender, cast(null as unsigned integer) as height, weight, cast(null as unsigned integer) as shoesize, cast(null as unsigned integer) as bmi from table_2
  union all
  select age_grp, gender, cast(null as unsigned integer) as height, cast(null as unsigned integer) as weight, shoesize, cast(null as unsigned integer) as bmi from table_3
  union all
  select age_group, gender, cast(null as unsigned integer) as height, cast(null as unsigned integer) as weight, cast(null as unsigned integer) as shoesize, bmi from table_4
) x
group by age_grp, gender;

我很驚訝CAST(NULL AS INT)導致語法錯誤，btw。 我必須將其更改為CAST(NULL AS UNSIGNED INTEGER) 。

SQL提琴： http ://www.sqlfiddle.com/#!2 / f4fa5c /1 。