Write a query to change the datatype of the column starttime to datetime in the table 'bookings' and make it as Not null column.Refer the existing DDL of table below.Existing DDLThe required input table is created in the back end.

To change the datatype of the column 'starttime' to datetime and make it as Not null in the table 'bookings', you can use the ALTER TABLE statement in SQL. Here is a step-by-step guide:

1. First, you need to ensure that all existing data in the 'starttime' column can be converted to datetime. If there are any values that cannot be converted, you will need to update or delete these rows.

2. Once you have ensured that all data can be converted, you can use the ALTER TABLE statement to change the datatype of the column. Here is the SQL command:

ALTER TABLE bookings
ALTER COLUMN starttime TYPE TIMESTAMP USING starttime::TIMESTAMP;

3. To set the column as NOT NULL, you can use the following command:

ALTER TABLE bookings
ALTER COLUMN starttime SET NOT NULL;

Please note that these commands are for PostgreSQL. The exact syntax might vary depending on the SQL dialect you are using. Also, please be aware that altering a table's structure can be a risky operation if not done properly, especially when it involves changing the datatype of a column. Always make sure to backup your data before performing such operations.