SQL Filters

This tutorial covers SQL Filters.

In this section, filters refer to statements that help with the retrieval of specific information

We cover Select Distinct and Select Top in this page. These filters work well with the “select” and “where” statements.

This page encompasses:

Let’s use the table “student_info” from the previous tutorials.

id	firstName	lastName	age
1	John	Smith	21
2	Patrick	Casey	26
3	Sam	Adams	19
4	Mike	Garcia	NULL
5	Patrick	Dumont	21

Select Distinct

As the name suggest, this statement filters only distinct (or different) data records.

By different, it means that duplicate values will not display.

The keyword is “distinct” and it is placed after the “select” statement.

The following is an example.

SELECT DISTINCT firstName
FROM student_info;

The above statement lists all unique names (no duplicates).

You will often have to work with very large databases.

And sometimes, we need only a few records. Instead of displaying hundreds or thousands of data records, we can use the “select top”.

The “select top” filters data and outputs a pre-specified number of records.

SELECT TOP 2 id, firstName, lastName
FROM student_info;

id	firstName	lastName
1	John	Smith
2	Patrick	Casey