MySQL Error Occurred

Error Message:
1021: Disk full (/var/mysqltmp/#sql_6b78_21.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")

SQL:
SELECT DISTINCT ( I.productId ), C.cat_id, I.productCode, I.description, I.image, I.price, I.name, I.popularity, I.sale_price, I.stock_level, I.useStockLevel, description,image,weight,price,pkr_list_price,amz_price,amz_list_price,name,sale_price,prod_flag,status FROM cubecart_cats_idx AS C INNER JOIN cubecart_inventory AS I ON C.productId = I.productId WHERE prod_flag=0 AND status=0 AND C.cat_id >0 AND ( I.cat_id=18122017043108 OR C.cat_id=18122017043108 ) GROUP BY I.productId order by productId DESC