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SELECT GROUP_CONCAT(CONCAT(a.first_name,' ',a.last_name) SEPARATOR ',') FROM customer AS a JOIN customer AS b WHERE SUBSTR(a.first_name,1,1)=SUBSTR(b.first_name,1,1) AND SUBSTR(a.last_name,1,1)=SUBSTR(b.last_name,1,1) GROUP BY SUBSTR(a.first_name,1,1), SUBSTR(b.first_name,1,1)

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