MySQL 8.0

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CREATE TABLE remunerations
AS
SELECT 2000 AS anyo_trab, 12 AS mes_trab
SELECT DATE_SUB(CONCAT(MAX(rm.anyo_trab),'-', MAX(rm.mes_trab),'-15'), 
            INTERVAL '0-0' YEAR_MONTH) AS fecha2
FROM
                remunerations rm

fecha2

2000-12-15

SELECT CAST(CONCAT(MAX(rm.anyo_trab),'-', MAX(rm.mes_trab),'-15') AS DATE) AS fecha2
FROM remunerations rm

fecha2

2000-12-15