SQL is used to query and extract information from a database. So in this blog post, you will learn about the standard SQL commands that often used to query a database.

Let’s say you have a collection of data stored in the following data table:

1. SELECT  is used to retrieve selected information that match the criteria specified.

SELECT column1, column2, ….. columnN

FROM table_name 

Using the example from the table above (CUSTOMER):

SELECT customer_id, last_name, first_name, age

FROM CUSTOMER;

2. If need to select all the columns available in the table then just use *.

SELECT  * FROM table_name;

Using the example from the table above (CUSTOMER):

SELECT * FROM CUSTOMER;

3. A clause known as “WHERE” can be used to extract specific row observations from the table. You can also specify a condition using comparison operators such as the following:

= (equal)

!= OR <> (not equal)

> (greater than)

< (less than)

>= (greater than or equal)

<= (less than or equal)

and so on. 

Using the example from the table above (CUSTOMER):

SELECT * FROM CUSTOMER

WHERE age > 35; 

OR

SELECT * FROM CUSTOMER

WHERE last_name = “Long”; 

Single quotes (“text“) must be used for characters or strings.

Categories: SQL Learning

Tags: sql basic, sql select