All language subtitles for 9. WHERE

In the last video, we learned how to retrieve all the rows of the table.

Let us now look at how to retrieve data, which is satisfying a particular specified condition.

Condition is specified using the clause.

Let us see the syntax of this clause.

It starts with select.

You enter all the column names which you want to retrieve from the table name, and then you specify

the condition after the where clause.

Let us look at some examples of these conditions.

Let's say we want to find out if there is any customer who is 25 years old.

This is how we do it.

Select first name from Customer table where age is equal to 25.

This age is equal to 25 will be the condition.

If it is satisfied, we will get a response back.

If it is not, we will get a null response back.

Let us run this query.

Select first name.

From customer table.

Where it is equal to.

25.

Only the customer with first name G is having age 25.

If you wanted the distinct values, you could have used select distinct roles that would have given

you distinct response.

Let us do that.

Run it.

You see, only one G returned.

Now, if you want to put a condition of age more than 25.

You can just change this equal to sign to greater than sign.

And then run this query.

The condition that we apply right now is numeric and correct.

That is, we are checking if that particular number is equal to or more than 25 or not.

We can put conditions on textual variables also.

You can match the variable.

So, for example, if you want to get all the information of the customer with first name G.

We will select star.

From customer table.

We're.

First name.

The.

This query.

You can see all the columns have been retrieved, but only those rows we have got as a result which

have first name as G.

One more thing you can note is in the previous query, we retrieved only first name, but we put a check

on the Age column.

So these two columns were different.

This is allowed by PostgreSQL.

So some variants of the SQL Server would make it necessary that the column on which you put your condition

is part of your selected columns.

But the way we wrote the query that is allowed by PostgreSQL.

So in this video we learned how to put condition while retrieving data.

Next, we will learn how to put multiple conditions at the same time in the same query using an and

or operator.