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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '40a208754b911f20fdc32cfef15d3e5c268c8ee08567138977e3738782a444b3' 
  AND token = '6+UCUYpF0rcE+B6uvt2mmnWmZbshOMV9i110+PIrXRs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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