Skip to main content

SELECT

SELECT is one of the most widely used commands in SQL. This command is used to select data from a database. The data returned is stored in a results table, also called the result-set.

Syntax​

The simplest way to use the SELECT statement is to return all columns from a table. This can be done with the following syntax:

SELECT * FROM table_name;

This will return all fields (columns) of all records (rows) from the table.

If you want to select just certain columns, you can specify them by name, separated by commas:

SELECT column_name1, column_name2 FROM table_name;

SELECT DISTINCT​

The SELECT DISTINCT statement is used to return only unique values in the output. It can be used to eliminate duplicate values in the returned data.

SELECT DISTINCT column_name FROM table_name;

WHERE Clause​

The WHERE clause is used to filter records. The WHERE clause is used to extract only those records that fulfill a specified condition.

SELECT column_name FROM table_name WHERE condition;

ORDER BY​

The ORDER BY keyword is used to sort the result-set in ascending or descending order. The ORDER BY keyword sorts the records in ascending order by default. If you want to sort the records in descending order, you can use the DESC keyword.

SELECT column_name FROM table_name ORDER BY column_name ASC|DESC;

Aggregate Functions​

Aggregate functions in SQL are functions where the values of multiple rows are grouped together to form a single value of more significant meaning, such as a list, a set, or a sum. Some examples include SUM(), COUNT(), MIN(), MAX(), and AVG().

SELECT COUNT(column_name) FROM table_name WHERE condition;
SELECT AVG(column_name) FROM table_name WHERE condition;
SELECT SUM(column_name) FROM table_name WHERE condition;
SELECT MIN(column_name) FROM table_name WHERE condition;
SELECT MAX(column_name) FROM table_name WHERE condition;

GROUP BY​

The GROUP BY statement is often used with aggregate functions (COUNT, MAX, MIN, SUM, AVG) to group the result-set by one or more columns.

SELECT column_name1, COUNT(column_name2) FROM table_name WHERE condition GROUP BY column_name1 ORDER BY COUNT(column_name2) DESC;

HAVING Clause​

The HAVING clause was added to SQL because the WHERE keyword could not be used with aggregate functions. It works like the WHERE clause but on grouped records.

SELECT column_name, COUNT(column_name) FROM table_name GROUP BY column_name HAVING COUNT(column_name) > value;

The above are the most common uses of the SELECT keyword in SQL. There are other keywords and functions you can use to manipulate the data as well. These will give you a good start on using SELECT in your SQL queries.