SELECT中的MySQL CASE语句

Question

I have a MySQL query question. I built a table that keeps track of high school football scores. It looks like this:

CREATE TABLE `games` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `home_team` int(11) NOT NULL,
  `visitor_team` int(11) NOT NULL,
  `home_score` tinyint(4) NOT NULL,
  `visitor_score` tinyint(4) NOT NULL,
  `quarter` tinyint(4) NOT NULL,
  `week` tinyint(2) NOT NULL,
  `game_date` date NOT NULL,
  `game_time` time NOT NULL,
  `complete` tinyint(4) NOT NULL DEFAULT '0',
  `stadium_id` int(11) NOT NULL,
  `created_at` datetime NOT NULL,
  `updated_at` datetime NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=151;

The query that I am doing uses a team's id to compare with. I want to retrieve the id values of the teams that the given team id defeated only. Here is my query so far.

SELECT 
    CASE 
        WHEN games.home_team != ? AND (games.home_score > games.visitor_score) THEN games.home_team 
        WHEN games.visitor_team != ? AND (games.home_score < games.visitor_score) THEN games.visitor_team 
    END AS id, teams.class_id, classes.name 
FROM games 
    INNER JOIN teams ON id = teams.id 
    INNER JOIN classes ON teams.class_id = class.id
    WHERE games.complete = 1

When I run this query in PHP MyAdmin I get the following error:

#1052 - Column 'id' in on clause is ambiguous

I am using PDO's execute() so the ?'s represent team id values. I figured since I assigned the result of my CASE statements to id, then I could use it to join the teams table. Can anybody point me in the right direction to fix this error? Thank you in advance.

Answer 1

You need to use either the table name in front of columns present in multiple tables, or use an alias:

INNER JOIN teams ON games.id = teams.id 

Edit: Having said that, it seems that it is in fact a column alias, which you can't do as is:

INNER JOIN teams ON
CASE 
    WHEN games.home_team != ? AND (games.home_score > games.visitor_score) THEN games.home_team 
    WHEN games.visitor_team != ? AND (games.home_score < games.visitor_score) THEN games.visitor_team 
END  = teams.id 

You could also use a subquery first, then match the results without the extra case statement.

Select
    sub.id,
    teams.class_id,
    classes.name
from
    (
        SELECT 
            CASE 
            WHEN games.home_team != ? AND (games.home_score > games.visitor_score) THEN games.home_team 
            WHEN games.visitor_team != ? AND (games.home_score < games.visitor_score) THEN games.visitor_team 
            END AS id
        FROM 
            games
        WHERE 
            games.complete = 1
    ) sub
    INNER JOIN teams ON sub.id = teams.id 
    INNER JOIN classes ON teams.class_id = class.id

Answer 2

I made a simple function to make that. It´s working.

// get variable
$area = $_GET['area'];

// function
function cases($a) {

    $sel_dash = mysql_query("SELECT * FROM sys_dash WHERE area = '$a'");
    $dados = mysql_fetch_assoc($sel_dash);
    $page = $dados['page'];

    return $page;
}

// call function with the variable
$page = cases($area);

To test if the value that you get it´s correct you can change the "return" to "echo" and the variable will be write in the code.

The table that i use is:

CREATE TABLE `sys_dash` (
    `id` INT(10) NOT NULL AUTO_INCREMENT,
    `area` VARCHAR(250) NOT NULL,
    `page` VARCHAR(250) NOT NULL,
    PRIMARY KEY (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
ROW_FORMAT=DEFAULT

I hope i help !

It´s note CASE class for PHP but have the same function that i need.

Thanks

Doniani