使用UNION查询3个表仅适用于其中2个表

Okay so I have three user tables separated intentionally. I have written some PHP to allow any user (Designer/Developer/Employer) to log in using a UNION query however this only works with the Developer and Employer tables. As soon as I add the Designer table to the query, it is impossible to log in. If I use just the Designer table in the query, that also works. Any ideas?

This used to work but now doesn't (Developers, Employers and Designers

$email = clean_string($db_server, $email); 
$password = clean_string($db_server, $password);
$query = "SELECT * FROM connectdDB.developers WHERE developers.email='$email' UNION SELECT * FROM connectdDB.employers WHERE employers.email='$email' UNION SELECT * FROM connectdDB.designers WHERE designers.email='$email'"; 
$result = mysqli_query($db_server, $query);

This works (Developers & Employers)

$email = clean_string($db_server, $email); 
$password = clean_string($db_server, $password);
$query = "SELECT * FROM connectdDB.developers WHERE developers.email='$email' UNION SELECT * FROM connectdDB.employers WHERE employers.email='$email'"; 
$result = mysqli_query($db_server, $query);

This works (Just Designers)

$email = clean_string($db_server, $email); 
$password = clean_string($db_server, $password);
$query = "SELECT * FROM connectdDB.designers WHERE designers.email='$email'"; 
$result = mysqli_query($db_server, $query);

Designers

id  | firstname | lastname | email | password | jobtitle | age | experience | bio | speciality
--------------------------------------- ------------------------------------------------------

Developers

id  | firstname | lastname | email | password | jobtitle | age | experience | bio | 
--------------------------------------- -------------------------------------------

Employers

id  | firstname | lastname | email | password | businessname | businesstype | businesswebsite | businessbio |
-------------------------------------------------------------------------------------------------------------

Designers has 10 columns the others have 9 columns.Union requires the same number of columns,what you could do is specify the columns

SELECT col1,col2... FROM t1 UNION SELECT col1,col2... FROM t2

Use aliases to homogenize the column names.