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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b51d617b55f42d2f6fe7d8b8299f45f78a8e36cf05f736cca1a80d3974b6ae8c' 
  AND token = 'R2d1+t+vEkowTuvpBvAgbLzT0L4GK9WJ557TKBbYbTI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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