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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '645de790f0af39519bb762d7c692290559b36d390dc8c3e100afd5e1935e9d27' 
  AND token = '1j2jKMvlk+El7sBvyAhaawx1PoYSacd1YrKloNai7sA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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