In different databases, the syntax of selecting top N records are slightly different. They may also differ from ISO standards.
In Oracle database, you can select from dual table if you only want to return a one row result set. In many other databases, the query engine supports select directly from constant values without specifying a table name.
JSON is commonly used in modern applications for data storage and transfers. Pretty much all programming languages provide APIs to parse JSON.
This code snippet shows how to convert string to date.
This code snippet shows how to calculate time differences.