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"
      ]
    }
  }
}