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SELECT 
  a.modifier, 
  a.modifier_type, 
  IF(
    shared_option_variants.variant_id IS NOT NULL, 
    shared_option_variants.modifier, 
    a.modifier
  ) as modifier, 
  IF(
    shared_option_variants.variant_id IS NOT NULL, 
    shared_option_variants.modifier_type, 
    a.modifier_type
  ) as modifier_type, 
  a.variant_id 
FROM 
  cscart_product_option_variants a 
  LEFT JOIN cscart_ult_product_option_variants shared_option_variants ON shared_option_variants.variant_id = a.variant_id 
  AND shared_option_variants.company_id = 1 
WHERE 
  1 
  AND a.variant_id IN (
    234725, 233820, 233853, 233870, 234752, 
    233930, 233945, 233976, 234004, 234042, 
    234009, 234031, 234020, 234079, 234092, 
    233977, 234753, 232064
  )

Query time 0.00058

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "shared_option_variants",
      "access_type": "system",
      "possible_keys": ["PRIMARY", "company_id"],
      "rows": 0,
      "filtered": 0,
      "const_row_not_found": true
    },
    "table": {
      "table_name": "a",
      "access_type": "range",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["variant_id"],
      "rows": 18,
      "filtered": 100,
      "attached_condition": "a.variant_id in (234725,233820,233853,233870,234752,233930,233945,233976,234004,234042,234009,234031,234020,234079,234092,233977,234753,232064)"
    }
  }
}

Result

modifier	modifier_type	variant_id
0.000	A	232064
0.000	A	233820
0.000	A	233853
0.000	A	233870
0.000	A	233930
0.000	A	233945
0.000	A	233976
0.000	A	233977
0.000	A	234004
0.000	A	234009
0.000	A	234020
0.000	A	234031
0.000	A	234042
0.000	A	234079
0.000	A	234092
0.000	A	234725
0.000	A	234752
0.000	A	234753