MySQL为每个公司ID基于其他多个行插入新行

Question

I have a MySQL database with many companies (several hundred). For each company I need to insert a single row in a new table that combines data from two rows in another table. Kind of like this:

For each company in Companies{
  Get min(AgeInMonths) as YoungestGroup from AgeGroups where companyid = company;
  Get max(AgeInMonths) as OldestGroup from AgeGroups where companyid = company;
  Insert YoungestGroup,OldestGroup,CompanyId into CombinedAgeGroups
}

My table structure is (basically) as follows:

Companies

• CompanyId
• CompanyName

AgeGroups

• AgeGroupId
• CompanyId
• AgeInMonths

CombinedAgeGroups

• CompanyId
• YoungestGroupId
• OldestGroupId
• MaxGroupSize

So in the CombinedAgeGroups table I will need to end up with a single row for each company. How do I loop through all the companies, get the youngest group and the oldest group out of the AgeGroups table for each company, and insert those values into CombinedAgeGroups?

Answer 1

You can use INSERT ... SELECT with a grouped query:

INSERT INTO CombinedAgeGroups (
         CompanyId, YoungestGroupId , OldestGroupId
)
SELECT   CompanyId, MIN(AgeInMonths), MAX(AgeInMonths)
FROM     AgeGroups
GROUP BY CompanyId