generate a unique and random number and save it when a row insert or update

1. run create_table file query's to create a table (the_table) with one column (rand)
2. now run create_random_number_function file query's to create a function for generating unique random number note that in this function table name and column name are important because we make query to check existing number if you have different name the you need to change in in this file
3. run create_trigger file query's to create a trigger . we use trigger to apply function in insert or update query's
4. now we need to apply trigger to the table use query's in file add_trigger_to_table. note that we used table name in here so be careful
5. now you can insert or update a row to generate and save a new unique random number