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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '50ca2df03e10ac991369744adaff10c766c20d67faf0b79dba73f8c3d548e7d2' 
  AND token = '5hDnwyJzrx+ad/X1wQRNwnf4KoorU1g2fHLlCEPAMJE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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