Hey there, welcome back to part seven of topic three in our database class. In this video, I'm going to discuss modifying data by using the SQL update statement. And I'll also provide a live demonstration in SQL Server Management Studio. Now let's learn how we can update or change the values of existing data in the database. And we do that with the update statement in SQL. And the update statement is very straightforward, easy to use. Again, it's always just about learning the pattern. So in this case, we begin with the keyword update. And then we specify the name of the object whose data we want to update in this case, the employee table. So we're saying, hey, database, I want to change some data in the employee table. And then we're going to specify the new values. So we say set. And then the name of the column whose value we want to change, along with its new value. So in this case, we're changing the value of the phone column to 6572781234. And then we optionally can specify a where clause, which is like a filter that will tell the database where to apply this change. So we're saying I want to change the value of the phone number column to 6572781234. But only if the employee ID is equal to 29. So if we did not specify a where, then the database would assume that we want to change the value of the phone number column to 6572781234 for every row in the employee table. So if I were to run this statement alone, without the where clause, every phone number in the employee table would be changed to this value, because I didn't specify a filtering criterion. When this is here, it's only going to apply that change to rows where this condition is true where it's met. So assuming I only have one employee ID that has or one employee who has an employee ID of 29, then this statement would only update the phone number of one person in my employee table. But without this where clause, it would change the phone number for everybody in that table. Now this generally highlights an interesting phenomenon in SQL that I've noticed over the years, and that is often you can do the most damage with the shortest SQL statements. Okay, so this statement here is more complicated. It's longer and more complicated than it would be if that part were omitted. This is a simpler statement. But this statement here will change much more data or has the potential to change much more data in the employee table than this one. So if you leave out the where, the change that you tell it to make will apply to every row in the table. If you specify a where, however, the change that you're telling it to make will apply only to those rows where the condition specified after the where statement is met. All right, let's take a look at the next example in this case we're just changing the value of one column. But in this next example, we're simultaneously changing the value of two columns. So we're in this case updating records in our employee table and we're changing the value of department ID to two and the value of higher date to the 22nd of January 2021. Or any row in that table in the employee table where the employee ID is equal to 62, which probably is just one row. So basically the overall thing we're saying here is, hey database change department ID in the employee table to two and higher date to the 22nd of January 2021 for employee number 62. So the database will automatically look through the employee table will find the row for employee number 62 and it will change that employee's department ID to two. And their higher date to the 22nd of January 2021. So if you want to manipulate more than one column value at the same time, you do it using this approach just a comma separated list of column names and their new values. So set the department ID to two, set the higher date to the 22nd of January for the same employee employee number 62. And finally down here we see an example where there is no where clause and again. If you write something like this, it's going to apply the changed every row in the table. So we were a very large say multinational corporation with, I don't know, 200,000 employees and you ran this SQL statement. It would change the value of department ID in your employee table for all 200,000 employees right so this one statement would make 200,000 changes to the table. Because you did not specify a where clause. So got to be careful with this right you can really cause a lot of damage with the one simple little statement. All right. Just taking a look at some quick live examples of this here we see some data we have project three project four project five. And let's see some updates. Okay, so instead of an insert. Let's update our project table. And we will set the project name to, I don't know, test project where the project ID is equal to four. Oh, if I go ahead and run this see we update one row in the table. And if I take a look at the data again, you'll see that we've changed the project name for project number four to test project. But again, if I leave this out. So I'm going to apply that changed every row in the table. I run this see it's affected six rows. And if we look at our data. We'll see the project name is now project test project for all of them. And importantly, there's no on do button. Right, so I can't just undo those changes easily to undo them. I would need to do something called a rollback. Which means that we'd have to look at the transaction log file and work backwards. And restore the previous values to their to what they used to be.