如何从带有乘法表的数据库中获取数据？

Question

Hello Guys!

I have a problem with get result from database correctly. I have lot of table but this is not important right now. I have a table look like that:

***PUBLISHER_DEVELOPER table***
pd_id : [int] AUTO PRIMARY
pd_name: [varchar]
pd_type: [integer] (0,1 or 2)

***GAME_INFO table***
g_id: [int] AUTO PRIMARY
g_label: [varchar]
g_publisher: [integer]
g_developer: [integer]

The connections beetwen the tables are this:

PUBLISHER_DEVELOPER : GAME_INFO = 1:LOT

I would like to get the game info with the publisher and developers normal name, but i always got ZERO row returned.

My SQL query:

*SELECT pd_name, pd_name, g_label FROM PUBLISHER_DEVELOPER,GAME_INFO WHERE pd_id = g_publisher AND pd_id = g_developer*

Any idea what i do wrong?

Answer 1

Probably the publisher and developer are different. There should be a relationship between the first table and either the g_publisher or g_developer.

SELECT pd_name, pd_name, g_label FROM PUBLISHER_DEVELOPER INNER JOIN GAME_INFO ON pd_id = g_publisher

SELECT pd_name, pd_name, g_label FROM PUBLISHER_DEVELOPER INNER JOIN GAME_INFO ON pd_id = g_developer

Or

SELECT pd_name, pd_name, g_label FROM PUBLISHER_DEVELOPER LEFT OUTER JOIN GAME_INFO ON pd_id = g_publisher

Answer 2

如果g_publisher和g_developer都引用了PUBLISHER_DEVELOPER.pd_id，那么您可以两次连接到该表。

  SELECT pd_1.pd_name, pd_2.pd_name, gi.g_label FROM PUBLISHER_DEVELOPER pd_1, PUBLISHER_DEVELOPER pd_2, GAME_INFO gi WHERE pd_1.pd_id = gi.g_publisher AND pd_1.pd_id = gi.g_developer;

Answer 3

Assumedly you want two joins to the PUBLISHER_DEVELOPER table to get back both the publisher and the developer.

SELECT p.pd_name AS p_name, d.pd_name AS d_name, g_label
FROM GAME_INFO
JOIN PUBLISHER_DEVELOPER p ON p.pd_id = g_publisher
JOIN PUBLISHER_DEVELOPER d ON d.pd_id = g_developer

SQL Fiddle example

For the query in your comment, a similar rewrite would look something like this.

SELECT f.fk_nev, k.fk_nev, k_nev, j_cim, j_megjelent, j_megjelenes, 
  j_cover, a_becenev, b_head, b_ci?m, b_cimke, b_lead, b_tartalom, 
  b_komment, b_datum, b_burl
FROM jatek_info ji
JOIN fejleszt_kiad f ON f.fk_id = ji.j_fejleszt  
JOIN fejleszt_kiad k ON k.fk_id = ji.j_kiad
JOIN jatek j ON j.j_jatek_info = ji.j_id  
JOIN blog b ON b.b_jatek = j.j_id
JOIN admin a ON a.a_id = b.b_szerzo

I'm guessing to a certain extent how your tables are linked, but I think that should be correct.

Note that there is a ? in one of the field names which I'm assuming is a non-ASCII character that got corrupted when you cut and paste the query into the comment. Be sure to fix that if you're cutting and pasting my code back.