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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '2c8346378776820c739a014606be08439001e9d5d6534a840d0e507b0fdb977c' 
  AND token = 'j6yQFgoWCYoY5WpNdJMQHQehRHktRP7+p1qA0NPEC4A=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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