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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, 234341, 234386, 234369, 234393, 
    234394, 234430, 234446, 234479, 234486, 
    234495, 234506, 234517, 234574, 234559, 
    234546, 233977, 234759, 232064
  )

Query time 0.00045

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": 19,
      "filtered": 100,
      "attached_condition": "a.variant_id in (234725,234341,234386,234369,234393,234394,234430,234446,234479,234486,234495,234506,234517,234574,234559,234546,233977,234759,232064)"
    }
  }
}

Result

modifier	modifier_type	variant_id
0.000	A	232064
0.000	A	233977
0.000	A	234341
0.000	A	234369
0.000	A	234386
0.000	A	234393
0.000	A	234394
0.000	A	234430
0.000	A	234446
0.000	A	234479
0.000	A	234486
0.000	A	234495
0.000	A	234506
0.000	A	234517
0.000	A	234546
0.000	A	234559
0.000	A	234574
0.000	A	234725
0.000	A	234759