如何在MYSQl中合并多个共有两列的表

我有四张桌子表1，表2，表3和表4。所有四个都有如下列：

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

我想创建一个包含列的新表：

age_grp, gender, height, weight, shoesize, BMI

---

我只希望合并所有表中年龄和性别相同的列。你知道怎么做吗？

可以通过以下方式轻松完成：

如果您要求所有表中的所有数据在列中具有相同的值，则可以将任何表与任何表连接起来

---

请注意，在实际生产脚本中不应使用

*

，请明确使用列名。

这可以通过以下方式轻松实现：

如果您要求所有表中的所有数据在列中具有相同的值，则可以将任何表与任何表连接起来

---

请注意，在实际生产脚本中不应使用

*

，应明确使用列名。

很可能无法通过纯匹配获得所需的结果。例如，以下内容将创建您描述的表：

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;

---

问题是，如果其中任何一项失败，就不会得到一行。你可以考虑使用外部连接。

< P>有一个很好的机会，你不会得到一个纯粹的匹配你想要的结果。例如，以下内容将创建您描述的表：

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;

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;

---

问题是，如果其中任何一项失败，就不会得到一行。你可以考虑使用外部连接。

尽管这个请求已经被回答了，但是我想给丢失的值的情况添加一个答案，例如，对于一个AGEGEGRP/性别对，只有SueSeIe。

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;

对于具有连接的解决方案，您需要MySQL不支持的完整外部连接。用左外联接和/或右外联接来模拟这一点对于几个表来说可能是一件痛苦的事情

这里是一个使用联合调用和最终聚合的解决方案

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;

我很惊讶

CAST（NULL为INT）

会导致语法错误，顺便说一句。我不得不将其更改为

CAST（NULL为无符号整数）

---

SQL fiddle:。

尽管此请求已经得到了回答，但我想为缺少值的情况添加一个答案，例如，对于年龄/性别对，仅给出鞋码

对于具有连接的解决方案，您需要MySQL不支持的完整外部连接。用左外联接和/或右外联接来模拟这一点对于几个表来说可能是一件痛苦的事情

这里是一个使用联合调用和最终聚合的解决方案

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;

我很惊讶

CAST（NULL为INT）

会导致语法错误，顺便说一句。我不得不将其更改为

CAST（NULL为无符号整数）

---

SQL FIDLE:。

对于第三个和第四个，我可以在逗号后添加名称吗？@VMAtm我有类似的查询，想优化LINQquery@ArijitMukherjee在使用LINQ时，您应该提出不同的问题。但是，

JOIN

s无法轻松优化。@VMAtm无法将此对话带到聊天室？@VMAtm非常感谢。请不要介意我问这个问题，但我只有一个小问题。现在我不希望年龄和性别重复出现。我的意思是现在新的部分有像

age\u grp

gender

height

age\u grp

gender

weight

等行。对于第三行和第四行，我可以在逗号后添加名称吗？@VMAtm我有类似的查询，想要优化LINQquery@ArijitMukherjee在使用LINQ时，您应该提出不同的问题。但是，

JOIN

s无法轻松优化。@VMAtm无法将此对话带到聊天室？@VMAtm非常感谢。请不要介意我问这个问题，但我只有一个小问题。现在我不希望年龄和性别重复出现。我的意思是现在新的部分有像

age\u grp

gender

height

age\u grp

gender

体重

等行。