I've been trying several times to use your code, but I obviously don't know what I'm doing,

Here is what is regenerated:
SELECT
`#__ezrealty`.`smalldesc` AS `title`,
`#__ezrealty`.`id`,
`#__ezrealty`.`cid`,
`#__ezrealty`.`price`,
`#__ezrealty`.`locality`
FROM `#__ezrealty`
WHERE
`#__ezrealty`.`published` = '1'
AND (`#__ezrealty`.`language` = '*' OR `#__ezrealty`.`language` = {langtag})
ORDER BY
`#__ezrealty`.`adline` ASC

I try variations on:
SELECT CONCAT_WS(',', `#__ezrealty`.`smalldesc`, `#__ezrealty`.`locality`,`#__ezrealty`.`price`) AS title
FROM `#__ezrealty`
WHERE
`#__ezrealty`.`published` = '1'
AND (`#__ezrealty`.`language` = '*' OR `#__ezrealty`.`language` = {langtag})
ORDER BY
`#__ezrealty`.`adline` ASC

but no result.

Where is my mistake?