错误1241（21000）：操作数应包含1列-School项目

Question

SELECT naam, adres, postcode, plaats, telefoon  
FROM klanten 
WHERE plaats IN (SELECT * FROM(
                    (SELECT plaats, COUNT(plaats) AS W 
                     FROM klanten 
                     GROUP BY plaats 
                     ORDER BY W DESC LIMIT 1) AS T));

So, where did I goof? Where is my syntax mistake or am I derping.

My goal is to print name (naam), adres (address), place (plaats), telephone (telefoon) from the city where the most customers (klanten) live.And before you ask, I'm doing this for a school project and we have to use an older version of MySQL that doesn't allow LIMIT 1 in subqueries. That's why the Select * FROM is there with the subquery.

Answer 1

The query you are trying to write looks like this:

SELECT naam, adres, postcode, plaats, telefoon
FROM klanten
WHERE plaats IN (SELECT plaats
                 FROM klanten
                 GROUP BY plaats
                 ORDER BY COUNT(*) DESC
                 LIMIT 1
                );

The syntax error is because the IN subquery is returning two columns -- that is pretty obvious from the message. The subquery in the subquery is not necessary; you can ORDER BY an aggregation expression.

Also, IN is a bit misleading. You can just use = .