Select in multiple columns with dot in the name does not return result

Question

Each column is composed of names, Fulano, Ciclano, Beltrano etc. I want to select all names that are different. If there is a Joaquin in two columns, you must return one to me. But the problem is not there, it is in the name of the columns that contains point col.A col.B col.C I do not know if this is allowed, I have not read anything against but the case is that it does not funf neither without [ ] nor with [ ].

Nevertheless , the reason for the question is to know if there is any specification against or any way to run with dot in the names of the columns

   $result = mysql_query("SELECT DISTINCT [col.A] FROM stabela UNION SELECT DISTINCT [col.B] FROM stabela UNION SELECT DISTINCT [col.C] FROM stabela");

    while($row = mysql_fetch_array($result)){
      $nome=$row['col.A'];
    }

Warning: mysql_fetch_array(): supplied argument is not a Valid Mysql result Resource in .... on line 58

Line 58 is (while($Row = mysql_fetch_array($result)))

Answer 1

Have you tried taking the clasps off?

SELECT DISTINCT 
    col.A
FROM stabela 

UNION 
SELECT DISTINCT 
    col.B
FROM stabela 

UNION 

SELECT DISTINCT 
    col.C
FROM stabela

Answer 2

I will post here the solution found in the Mysql Certification Study Guide and also in the documentation recommended by our friend Anderson Carlos Woss Schema Object Names

Put the column names in the query between inverted single quotes.

$query = mysql_query("SELECT DISTINCT `col.A` FROM stabela UNION SELECT DISTINCT `col.B` FROM stabela UNION SELECT DISTINCT `col.C` FROM stabela");

These inverted quotes are nothing more than the crase accent of your keyboard. Shift + accent key and space key. I ran the test on DB and rotated round :)