Join one row to multiple rows in another table

Question

I have a table to entities (lets call them people) and properties (one person can have an arbitrary number of properties). Ex:

People

Name  Age
---         


        

Answer 1

You can use INNER JOIN to link the two tables together. More info on JOINs.

SELECT *
FROM People P
INNER JOIN Properties Pr
  ON Pr.Name = P.Name
WHERE P.Name = 'Joe' -- or a specific age, etc

However, it's often a lot faster to add a unique primary key to tables like these, and to create an index to increase speed.

Say the table People has a field id
And the table Properties has a field peopleId to link them together

Then the query would then look something like this:

SELECT *
FROM People P
INNER JOIN Properties Pr
  ON Pr.id = P.peopleId
WHERE P.Name = 'Joe'

Answer 2

Use:

   SELECT x.name,
          GROUP_CONCAT(y.property SEPARATOR ', ')
     FROM PEOPLE x
LEFT JOIN PROPERTIES y ON y.name = x.name
    WHERE x.age > 26
 GROUP BY x.name

You want the MySQL function GROUP_CONCAT (documentation) in order to return a comma separated list of the PROPERTIES.property value.

I used a LEFT JOIN rather than a JOIN in order to include PEOPLE records that don't have a value in the PROPERTIES table - if you only want a list of people with values in the PROPERTIES table, use:

   SELECT x.name,
          GROUP_CONCAT(y.property SEPARATOR ', ')
     FROM PEOPLE x
     JOIN PROPERTIES y ON y.name = x.name
    WHERE x.age > 26
 GROUP BY x.name

I realize this is an example, but using a name is a poor choice for referencial integrity when you consider how many "John Smith"s there are. Assigning a user_id, being a unique value per user, would be a better choice.

Answer 3

SELECT x.name,(select GROUP_CONCAT(y.Properties SEPARATOR ', ')
FROM PROPERTIES y 
WHERE y.name.=x.name ) as Properties FROM mst_People x 

try this