SELECT t1.id, t1.name, t1.population, CAST(SUM(t2.town_1) AS CHAR) AS town, CAST(SUM(CASE WHEN t2.id LIKE 23 THEN 1 ELSE 0 END) AS CHAR) AS population FROM area1 t1 LEFT JOIN area2 t2 ON t1.id = t2.id WHERE t1.id like 23
Normally it will match if id = 23 exist in both tables. But it's not the case (not in t1 table) so the request return NULL values.
How i can do to return no result?
If you only want the result to be matched if the ID exists in BOTH tables, you're looking for an INNER JOIN instead of a LEFT JOIN.
EDIT:
On second thought, it's because of your aggregate functions (SUM). You're casting them as CHARs (didn't even know you could do that). You should be using a GROUP BY. Try this:
SELECT
t1.id,
t1.name,
t1.population,
SUM(t2.town_1) AS town,
SUM(CASE WHEN t2.id LIKE 23 THEN 1 ELSE 0 END) AS population
FROM
area1 t1
INNER JOIN area2 t2
ON t1.id = t2.id
WHERE
t1.id like 23
GROUP BY
t1.id,
t1.name,
t1.population
On a side note, there's no need for the like in your WHERE clause. The way you have it, it's doing the same thing as an = sign.
