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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b3c1878fe42f65f70fd1254ca88c9fc6e6c54cbfa6825c94f6d4f4259efb46f2' 
  AND token = 'L8AiMJkGN1KUYSPn47OIvzeVFtDxtpvj7ShHl1sibos=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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