If you want to combine results from two select queries in MySQL you can use the “UNION” operator.
In the following examle the results from the users query and the customers query are combined and the final result will be a table with all the results.
(
SELECT
user_id, user_name
FROM
users
)
UNION
(
SELECT
user_id, user_name
FROM
customers
)
Note that the same column names must be in the select clause in both of the queries
Those are the maximum lenght for each MySQL identifier.
You can write names longer than the values in the table below
| Identifier | Maximum Length (characters) |
| Database | 64 |
| Table | 64 |
| Column | 64 |
| Index | 64 |
| Stored Function or Procedure | 64 |
| Trigger | 64 |
| View | 64 |
| Alias | 255 |
Every programmer comes to a situation when he has to compare two databases.
This can be the development and the production database in order to synchronize them or it can be any other two databases that needs to be structurally compared.
I found a very nice and simple free tool written in PHP that does the job very well.
The tool is called mysqldiff and it is a php application. Once you install it on your server you can compare any two MySQL databases.
Check it out.
You can download the tool from here
http://www.mysqldiff.org/downloads.php
