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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a51ce14c66773e4cd7c68fd04a1ef94e6e1bac0c712179af3f88d0a64bbd67a4' 
  AND token = 'DQ5kbPBhKlZLP3M0dByeF8om8DJEtWo0yis4lTFPsqM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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