Question

I am not a MySQL expert by any means, but after reading the documentation for the SELECT statement, I did not find an answer to my problem.

I have this statement:

SELECT COUNT(*)=x.c FROM someTable, 
    (SELECT COUNT(*) c 
     FROM someTable 
     WHERE firstId <= secondId) x;

And I’m trying to figure out what the x.c means in the context of the query? Specifically, what is with the x that seems to be hanging out there?

I interpret the nested SELECT as SELECT COUNT(*) as c, making an alias for the row count as c, is that what the x is as well? What would it be an alias for?

Thanks!

Answer 1

The x is a table alias – a name for the nested SELECT statement in parentheses.

COUNT(*)=x.c

Is a boolean condition that the total row count of someTable be equal to the row count of someTable where firstId <= secondId

x.c is the column name for the count returned by the subquery.