Month: June 2008

Using sub queries in the HAVING clause is little different than using a sub query in any other part of the clause. The one thing that may through you is the WHERE clause inside the sub query… it acts as a JOIN criteria, so you might not get the placement right, until you’ve done it…

Last time we discussed triggers, we covered insert triggers. This time we’re doing UPDATE triggers. All the same rules apply to UPDATE triggers that apply to INSERT triggers. CREATE TRIGGER t_tablename_update ON TableName AFTER|FOR|INSTEAD OF UPDATE AS T-SQL code Just like for the INSERT TRIGGER, we can either run the T-SQL code after the update…

I know I’ve covered sub queries before, but I wanted to make sure I made a specific point. When you create a correlated sub query, you can reference columns from your subquery anywhere in your outer query. Usually you’ll either use it in your SELECT clause or your WHERE clause, but you can use it…

Let’s look at the following code using your copy of AdventureWorks. USE AdventureWorks GO SELECT COUNT(*) AS countStar , COUNT(ALL EmployeeID) AS CountAllEmployeeID , COUNT(DISTINCT EmployeeID) as CountDistinctEmployeeID FROM HumanResources.JobCandidate You should get three counts countStar    CountAllEmployeeID    CountDistinctEmployeeID 13 2 2 You need to understand the differences in these counts. COUNT(*)  returns the number of…

The fundamental idea behind sub queries is you execute the sub query once, then take the value(s) from that sub query and substitute them in place of the sub query for the outer query. That’s quite a mouthful. Just think of it like this, the database engine will run the inner query, then replace the…

Every error generated in Microsoft SQL has a specific number, this number should uniquely identify the error that has occurred. This can be useful in building logic on what to do when a certain error is raised since creating a logic test for a number is far quicker than generating one for a string. Let’s…