1-1) Waitfor Delay '0:0:15' -- and Waitfor Delay '0:0:15' -- are two commonly used commands in SQL database management systems. While they may seem similar at first glance, there are key differences between the two that set them apart.

The main function of these commands is to cause a delay in execution. This is useful in certain scenarios where you need to slow down your query or prevent a certain action from happening too quickly. However, the way they achieve this delay is what sets them apart.

The '1-1' in Waitfor Delay '0:0:15' -- stands for 'one millisecond'. This means that the delay caused by this command will last for one millisecond. On the other hand, Waitfor Delay '0:0:15' -- does not have a specific time unit attached to it. Instead, it allows you to specify the time period in a more flexible way, such as 'seconds', 'minutes' or 'hours'.

Another key difference between these two commands is the fact that Waitfor Delay '0:0:15' -- allows you to specify a message to be displayed during the delay period. This can be useful for debugging or providing feedback to users. Waitfor Delay '0:0:15' -- does not have this feature.

When it comes to performance, there is not much difference between the two commands. Both can cause a significant delay in execution time, which can be beneficial or problematic depending on the situation.

In conclusion, while Waitfor Delay '0:0:15' -- and Waitfor Delay '0:0:15' -- may seem similar in function, they have distinct differences that make them suitable for different use cases. Consider your specific needs and the available parameters before deciding which one to use in your SQL statements.