SELECT 
  jmj_product_descriptions.product_id, 
  jmj_product_descriptions.short_description, 
  IF(
    jmj_product_descriptions.short_description = '' 
    OR jmj_product_descriptions.short_description IS NULL, 
    jmj_product_descriptions.full_description, 
    ''
  ) AS full_description 
FROM 
  jmj_product_descriptions 
WHERE 
  jmj_product_descriptions.product_id IN (
    938, 939, 942, 943, 944, 945, 946, 947, 
    948, 949, 951, 952, 953, 954, 956, 958, 
    960, 962, 963, 965, 967, 968, 969, 970, 
    972, 973, 974, 975, 976, 977, 978, 979, 
    980, 981, 984, 985, 986, 987, 988, 989, 
    990, 991, 992, 993, 994, 995, 996, 997
  ) 
  AND jmj_product_descriptions.lang_code = 'en'

Query time 0.01104

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "115.21"
    },
    "table": {
      "table_name": "jmj_product_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "product_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "product_id",
        "lang_code"
      ],
      "key_length": "9",
      "rows_examined_per_scan": 48,
      "rows_produced_per_join": 48,
      "filtered": "100.00",
      "index_condition": "((`jmj_test`.`jmj_product_descriptions`.`product_id` in (938,939,942,943,944,945,946,947,948,949,951,952,953,954,956,958,960,962,963,965,967,968,969,970,972,973,974,975,976,977,978,979,980,981,984,985,986,987,988,989,990,991,992,993,994,995,996,997)) and (`jmj_test`.`jmj_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "105.61",
        "eval_cost": "9.60",
        "prefix_cost": "115.21",
        "data_read_per_join": "183K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ]
    }
  }
}

Result

product_id short_description full_description
938 <p>BIGGER SIZE AVAILABLE ON DEMAND </p>
939
942
943
944
945
946
947
948
949
951
952
953
954
956
958
960
962
963
965
967
968
969
970
972
973
974
975
976
977
978
979
980
981
984
985
986
987
988
989
990
991
992
993
994
995
996
997