如何为下表编写SQL查询？

Question

My table is defined like this:

Name is a string and property too.

ID | Name | Property

An example for data in this table is this:

ID | Name | Property
1    Peter  Newsletter
2    Paul   Register
3    Peter  Register
4    Shaun  Newsletter
5    Steve  Register

Now I like to query all people that have the property newsletter and register. As a result I should get Peter, because he has both property's.

So the resulting table should be like:

ID | Name | Property
1    Peter  Newsletter
3    Peter  Register

So everything I try to query is which person has both property's newsletter and register.

Answer 1

Here is one method:

select t.*
from table t
where exists (select 1
              from table t2
              where t2.name = t.name and t2.property = 'NewsLetter'
             ) and
      exists (select 1
              from table t2
              where t2.name = t.name and t2.property = 'Register'
             );

If you just want the list of names, perhaps with id s, I would do that as:

select t.name
from table t
where t2.property in ('NewsLetter', 'Register')
group by t.name
having count(distinct property) = 2;

How you get the list of id s depends on your database, something like listagg() or group_concat() or string_agg() .

Answer 2

An alternative, pretty much on the same lines as Gordon's solution, but without using EXISTS :

select * from tablename
where name in (select name from tablename where property = 'Newsletter')
and name in (select name from tablename where property = 'Register')

Answer 3

It's hard to be sure without knowing more about the data. Given the exact requirements that you gave to us, this will give the results you showed:

WITH multprop (multName) AS (
   SELECT NAME FROM myTable
       WHERE Property IN('Newsletter','Register')
       GROUP BY NAME
       HAVING count(*)>1 )
select id, Name, Property
 from multprop inner join myTable
      on multName = Name

But minor differences in your requirements will mess things up. For example, will there ever be Property values other than the two you listed? Or can a Name show up multiple times with the same Property?

EDIT: The added WHERE clause limits rows in the CTE to the requested specific set of Property values. This is from the more detailed requirements in comments.

Answer 4

One more way:

SELECT * FROM T as T1
WHERE Property IN ('Newsletter','Register')
      AND EXISTS (SELECT * FROM T 
                      WHERE Name=T1.Name 
                            and Property IN ('Newsletter','Register')
                            and Property <> T1.Property
                 )

SQLFiddle demo

Answer 5

Another one, for the record

WITH cteHasBoth
 as (select Name
       from MyTable
       where Property in ('Newsletter', 'Register')
       group by Name
       having count(*) = 2)
 select ID, Name
  from MyTable
  where name in (select Name from cteHasBoth)

This would require only two sacns through the table.