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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a21f3a6deed61117fcbc0886af9281fe649d761058f9e7fc5c16687027c74a2f' 
  AND token = 'JydPPqdJrOY6ugDGJHYlupiDDXt1AiBVhxnmXaD9Brk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00039

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}