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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'f8921e2be09a177973faec5179267b61d08b26c77238e402500926a78ec5ebbd' 
  AND token = 'uxtnOlB1+3Pv0eC5nAZGQxvh9JiKuDLiMq1EW573sbk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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