Question

I have a database that which contains two tables, links and tour. Tour is defined as

+----+-------------+-----+-----+--------+---------+-------+---------+
| ID | FileName    | Lat | Lon | Name   | Heading | Width | Height  |
+----+-------------+-----+-----+--------+---------+-------+---------+

and links is defined as

+-----+------------+--------+
| ID  | locationID | linkID |
+-----+------------+--------+

links.locationID is a foreign key to tour.ID. What I want to do is grab all the links that match to a specific tour.name

Right now, I have to run these two queries and use the ID of the first as a variable for the second

SELECT * FROM tour WHERE tour.name = 'name'

SELECT * FROM tour
  INNER JOIN links ON tour.ID = links.linkID 
  WHERE links.locationID = ID of first query

How can I adapt this to a single search?

I’ve tried a subquery:

SELECT * FROM tour 
  INNER JOIN links ON tour.ID = links.linkID 
  WHERE links.locationID = ( SELECT * FROM tour WHERE tour.name = 'name')

This gives me an error 1241 saying that operand should contain one column.

I’ve looked up some examples of subqueries, but hey all lack the inner join statement I’m using. What modifications are necessary to this query?

Answer 1

SELECT links.*, tour.*
FROM links
JOIN tour ON tour.ID = links.linkID
JOIN tour AS location ON location.ID = links.locationID -- you must create an alias, in order to refer to this table without ambiguity
WHERE location.name = 'name';

As for your version with subquery, you could do:

SELECT * FROM tour 
INNER JOIN links ON tour.ID = links.linkID 
WHERE links.locationID = (
    SELECT ID -- "operand should contain one column"
    FROM tour WHERE tour.name = 'name'
);

But prefer the first option.