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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '76d09f5e39f9bc142007908ed2b3536a1c08f90dd94f4dfe6a3feb8e4c5b6661' 
  AND token = 'sTZLjy2gelu0dnATYgkWr8VAzE4r5b/6v5cmWo6aSG0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}