SELECT 
  cscart_cp_tag_ext_description.tag_id 
FROM 
  cscart_cp_tag_ext_description 
WHERE 
  tag like 'Books' 
  AND cscart_cp_tag_ext_description.company_id = 1

Query time 0.00045

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_cp_tag_ext_description",
      "access_type": "range",
      "possible_keys": ["tag"],
      "key": "tag",
      "key_length": "767",
      "used_key_parts": ["tag"],
      "rows": 1,
      "filtered": 100,
      "index_condition": "cscart_cp_tag_ext_description.tag like 'Books'",
      "attached_condition": "cscart_cp_tag_ext_description.company_id = 1"
    }
  }
}