如何为两个相关表创建MYSQL记录源

Question

I currently have a page that displays player information from one table named "tblplayers". The query I am currently using is:

$result = mysql_query("SELECT * FROM tblPlayers WHERE lng_RecordID_PK = '".$playerid."' ");

I have a second table named "tblMatches" containing match results for the players. I want the recordset to include the rows from "tblMatches" WHERE "P1_ID" OR "P2_ID" is equal to the "lng_RecordID_PK" field from "tblPlayers".

How can I revise my $result query so that it returns:

• one row from tblPlayers
• multiple rows from tblMatches

???

Thanks for helping me out.

Answer 1

That's called a 'join':

SELECT tblPlayers.*, tblMatches.*
FROM tblPlayers
LEFT JOIN tblMatches ON Ing_RecordID_PK IN (P1_ID, P2_ID)

Answer 2

You are asking about joining two tables where the second table potentially has multiple records for each one in the first table. This is a one-to-many or 1:N join, and most often done using a LEFT JOIN meaning you want everything in the "left" table, and all the records that match from the "right" table, and that you may have some records on the "left" side with no matches.

Your query would look like this:

SELECT *
FROM tblPlayers
LEFT JOIN tblMatches
    ON (tblPlayers.lng_RecordID_PK = tblMatches.P1_ID
        OR tblPlayers.lng_RecordID_PK = tblMatches.P2_ID)
WHERE tblPlayers.lng_RecordID_PK = @PlayerID;

Bits of advice:

• Avoid selecting all columns (*) and instead select just those that you need for the query.
• Consider using parameterized queries to avoid SQL injection attacks. If your variable were to be submitted or altered maliciously, it could result in compromised data or security. (See PHP Data Objects for example.)

Answer 3

There is no way to get rows from two different tables in the way you are describing. You could not get a row from one table, and two rows from another one. What you could is do two separate queries, or use a JOIN statement to join the two tables together, and then receive results from the resulting joined table. If you provide more information about your table structure I am sure more help can be given.