QUERY

SELECT SQL_NO_CACHE  SUM(GiftCouponFidelizationProducts.assignedpoints) as puntos FROM GiftCouponHistory LEFT JOIN GiftCoupon ON GiftCouponHistory.id_giftcoupon = GiftCoupon.id LEFT JOIN Unit ON GiftCouponHistory.id_unit = Unit.id LEFT JOIN GiftCouponFidelizationProducts ON GiftCouponHistory.id_giftcoupon = GiftCouponFidelizationProducts.id_giftcoupon WHERE GiftCouponHistory.date >= '2018-01-01 00:00:00' AND GiftCouponHistory.date <= '2018-12-31 23:59:59' AND GiftCouponHistory.id_unit != GiftCouponFidelizationProducts.id_unit AND GiftCouponHistory.bt_type = 4 AND GiftCouponHistory.id_unit =75 AND GiftCoupon.bt_offset = 1 GROUP BY GiftCouponHistory.id_unit;

SOLUCION, tras usar EXPLAIN (le recomendamos a la BD que user el index Unit de GiftCouponHistory):


SELECT SQL_NO_CACHE  SUM(GiftCouponFidelizationProducts.assignedpoints) as puntos FROM GiftCouponHistory USE INDEX(Unit) LEFT JOIN GiftCoupon ON GiftCouponHistory.id_giftcoupon = GiftCoupon.id LEFT JOIN Unit ON GiftCouponHistory.id_unit = Unit.id LEFT JOIN GiftCouponFidelizationProducts ON GiftCouponHistory.id_giftcoupon = GiftCouponFidelizationProducts.id_giftcoupon WHERE GiftCouponHistory.date >= '2018-01-01 00:00:00' AND GiftCouponHistory.date <= '2018-12-31 23:59:59' AND GiftCouponHistory.id_unit != GiftCouponFidelizationProducts.id_unit AND GiftCouponHistory.bt_type = 4 AND GiftCouponHistory.id_unit =75 AND GiftCoupon.bt_offset = 1 GROUP BY GiftCouponHistory.id_unit;