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SELECT 
  variant_id, 
  yml2_unit 
FROM 
  cscart_product_feature_variant_descriptions 
WHERE 
  variant_id IN (
    '92', '91', '88', '95', '93', '99', '94', 
    '136', '98', '89', '97', '55', '52', 
    '58', '49', '46', '39', '63', '61', 
    '59', '51', '41', '56', '53', '44', 
    '45', '47', '64', '50', '54', '48', 
    '60', '62'
  ) 
  AND lang_code = 'ru'

Query time 0.00394

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_feature_variant_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["variant_id", "lang_code"],
          "rows": 33,
          "filtered": 100,
          "index_condition": "cscart_product_feature_variant_descriptions.variant_id in ('92','91','88','95','93','99','94','136','98','89','97','55','52','58','49','46','39','63','61','59','51','41','56','53','44','45','47','64','50','54','48','60','62') and cscart_product_feature_variant_descriptions.lang_code = 'ru'"
        }
      }
    ]
  }
}

Result

variant_id	yml2_unit
39
41
44
45
46
47
48
49
50
51
52
53
54
55
56
58
59
60
61
62
63
64
88
89
91
92
93
94
95
97
98
99
136

variant_id	yml2_unit
39
41
44
45
46
47
48
49
50
51
52
53
54
55
56
58
59
60
61
62
63
64
88
89
91
92
93
94
95
97
98
99
136

variant_id	yml2_unit
39
41
44
45
46
47
48
49
50
51
52
53
54
55
56
58
59
60
61
62
63
64
88
89
91
92
93
94
95
97
98
99
136

variant_id	yml2_unit
39
41
44
45
46
47
48
49
50
51
52
53
54
55
56
58
59
60
61
62
63
64
88
89
91
92
93
94
95
97
98
99
136