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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '81b3d1d9bfa7e376e131bad69573e29b1253dcd9ceb1a87aa91612bc7cb4f15d' 
  AND token = 'k6rq+fxXvCeG10KW+3vgX4nsuXaE8coP7/5mpZLQyyg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00037

JSON explain

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