Search one table and use result to search another table - mysql

Question

I want to make a search on one table that returns a value to be used in search on different table.
I have this code, which looks for a team code in the club table:
SELECT Team, Teamcode
FROM epl.club
WHERE Teamcode =
(SELECT Teamcode
FROM epl.club
WHERE Team='Manchester City');
Now I want to use the resulting Teamcode for a select on the matches table.
I have this code that searches the matches table and finds all the matches with a given team code but I need it to get the code from the first search above.
Select *
from epl.matches
where HomeTeam = 35
or AwayTeam = 35
and FTR like "A"
or FTR like "H";
Another thing I don't understand is that I want to make that it would just return the line only if HomeTeam=35'= and '=FTR is A or FTR is H or if AwayTeam=35 and FTR is A or FTR is H, but what the code does is that it returns all the lines even if they contain the 35 but only contain the H or A in the FTR column.

Answer 1

You have to use parentheses in your boolean expression:
SELECT *
FROM epl.matches
WHERE (HomeTeam = 35 or AwayTeam = 35)
AND (FTR like "A" or FTR like "H")
This is because AND has a higher operator precedence as OR.
You can combine the queries with a join:
SELECT Team, Teamcode FROM epl.club c
INNER JOIN epl.matches m ON (m.HomeTeam = c.Teamcode or m.AwayTeam = c.Teamcode)
WHERE (c.Team = 'Manchester City')
AND (m.FTR like "A" or m.FTR like "H")
Additional info:
Here is a very simple explanation how a 'INNER JOIN' can be understood - just if you don't know this already. If you have two tables:
{ Table: Club }----------------| { Table: Matches }----------|
| | | |
| Teamcode | Team | | HomeTeam | AwayTeam | FTR |
|----------+-------------------| |----------+----------+-----|
| 35 | Manchester City | | 38 | 39 | A |
| 38 | Arsenal London | | 38 | 35 | A |
| 39 | Leeds United | | 35 | 39 | H |
|----------+-------------------| | 38 | 35 | A |
| 39 | 38 | H |
|----------+----------+-----|
an INNER JOIN between the tables club and matches means that of all row combinations of the two tables only the rows are included in the result if the join condition m.HomeTeam = c.Teamcode or m.AwayTeam = c.Teamcode is met. If you restrict club.Team to 'Manchester City' you would have the following result for the join:
{ Table: Join Result }------|
| |
| HomeTeam | AwayTeam | FTR |
|----------+----------+-----|
| 38 | 35 | A |
| 35 | 39 | H |
| 38 | 35 | A |
|----------+----------+-----|
It takes some time to get used to declarative style of the join syntax but it helps you to structure your queries (opposed to multiple FROM tables and nested SELECT subqueries). Furthermore, the SQL query optimizer can handle an INNER JOIN better then nested subqueries in most cases.

Answer 2

First query could just be:
SELECT
Team,
Teamcode
FROM epl.club
WHERE Team='Manchester City';
Why a subquery on the same table when you can access directly the Team field?
Then you can do:
SELECT *
FROM epl.matches
WHERE HomeTeam = (SELECT Teamcode FROM epl.club WHERE Team='Manchester City')
OR AwayTeam = (SELECT Teamcode FROM epl.club WHERE Team='Manchester City')
AND FTR like "A"
OR FTR like "H";