Concat 2 columns in a string, then get a count for each concatenation
<p>I am trying to concatenate 2 columns, then count the number of rows i.e. the total number of times the merged column string exists, but I don't know if it is possible. e.g:</p>

<pre><code>SELECT 
    CONCAT(column_1,':',column_2 ) as merged_columns, 
    COUNT(merged_columns) 
FROM 
    table 
GROUP BY 1
ORDER BY merged_columns DESC
</code></pre>

<p><strong>Note:</strong> the colon I've inserted as a part of the string, so my result is something like 12:3. The 'count' then should tell me the number of rows that exist where column_1 =12 and column_2 = 3.</p>

<p>Obviously, it tells me 'merged_columns' isn't a column as it's just an alias for my CONCAT. But is this possible and if so, how?</p>