SQL Where Archives - Page 3 of 3 - SQL Training Online

June 10, 2012 by Joey Blue Leave a Comment

SQL IN

The SQL IN clause is used when you are filtering data and you want to look for more than one value.

Let’s take a look at the following query:

select * 
from customer 
where customer_company = 'Dell' 
 or customer_company='HP' 
 or customer_company='Walmart';

This query says that we want all of the columns, from the company table, where the customer_company is either Dell, or HP, or Walmart.

Here are the results:

This query works great, but it means you have to type a lot more than you need to.

That is where the “IN” clause comes into play. Instead of typing “customer_company” 3 times like we did in the previous SQL Query, we can write the query as follows:

select * 
from customer 
where customer_company IN ('Dell','HP','Walmart');

The results of this query are the exact same as the results above.

Notice how much less typing I had to do. And, notice the syntax.

It goes column name (in this case customer_company), then you use the “IN” word, then you list all of the values in side of parenthesis and separated by commas.

That’s it. I often use the IN clause instead of a bunch of OR’s, because it is neater and easier for me to read.

As you start putting more complex queries together, it will be a lot easier to keep track of an IN clause instead of a bunch of OR statements.

Remember to put any question, comments, or other topics you would like for me to explain into the comment section below.

June 9, 2012 by Joey Blue Leave a Comment

SQL AND OR

The SQL AND OR is used when filtering with the SQL Where clause. More specifically, we are talking about the “AND” and the “OR” clauses.

Let’s start by looking at a basic SQL statement:

select * from customer

The customer table has the following records:

Now if we were to filter to just the “Dell” records, we would use the following query:

select * 
from customer 
where customer_company = 'Dell';

But, I want to get the “Dell” records and the “HP” records. To do that we would use the following query:

select * 
from customer 
where customer_company = 'Dell' 
 or customer_company='HP';

And we get the following results:

Now, you are probably asking, “You said we want Dell AND HP records, why did we use the OR clause?”

It can be a little confusing, but here is how I think of it.

In the case where we want the company of Dell and HP, we are actually saying we want all of the records where the customer_company is Dell or the customer company is HP.

There is a never a case where the customer_company is both Dell and HP.

So let’s look at an example where we use the AND statement.

If, I wanted to get all of the Dell customers that have a name of Bill, I would use the following query:

select * 
from customer 
where customer_company = 'Dell' 
 and customer_name='Bill';

In this case, I am actually looking for records where both criteria is met. Here is the result:

Those are the basics of using the SQL AND and OR clauses.

Please leave and questions or comments below and let me know if you want me to talk about any other topics.

June 8, 2012 by Joey Blue Leave a Comment

SQL Where

The SQL Where clause in the SQL Language allows you to filter data when you query a database.

Let’s look at the following query that gets data from the customer table:

select * from customer;

Here are the results:

Now, I only need to get the “Dell” customers. In order to do that, I have to use the where clause.

Let’s add that to the query:

select * from customer where customer_company='Dell';

When I execute this query, I get the following results:

So I have filtered the records from 6 down to 2.

Notice the following part of the query:

customer_company='Dell';

The red part is how Microsoft SQL Server represents a string. It knows it is a string, because of the single tick (‘) marks.

All strings need to be enclosed in these.

Let’s show an example where we want everyone except for Dell customers:

select * from customer where customer_company != 'Dell';

Instead of using the “=” sign, we use the “!=” which says “Not Equal”.

Here are the results:

We have filtered out the 2 Dell records.

That is the basics of the where clause.

Please leave any comments or questions below.