使用PDO在两个数据库之间连接

Question

I have two databases and I am trying to compare two tables. My code does not seem to be working, not sure what I am doing wrong.

Here is the code.

<?php
include 'connection.php';
/* 
 * This code compares between two tables
 */

//SQL call
$getData = $connection->prepare("SELECT `CustomerCity` FROM `auth` LEFT JOIN `tb_data.cobs.city` WHERE `CustomerCity` =  `tb_data.cobs.city` LIMIT 3");
$getData->execute();
$gotData = $getData->fetchAll(PDO::FETCH_ASSOC);
print_r($gotData);

In my database I have two tables, on is cobs, the other is tb_data. tb_data has a table called cobs and auth is a table within a database called d_data. Both of these tables have a city column. I need get every record in auth that has a city that matches in the cobs table.

Answer 1

The query is incorrect, you need to specify the link betweeen the tables auth and tb_data.cobs.city. For example:

SELECT
    * 
FROM 
    FOOTABLE FOO
LEFT JOIN
    BARTABLE BAR ON BAR.FOO_ID FOO.ID = -- here goes the link between them
WHERE
    ...