SQL SELECT Statement

The SELECT statement is one of the most commonly used SQL commands and is essential for retrieving data from a database. This tutorial will guide you through the basics of using the SELECT statement to query data from a single table.

What is the SELECT Statement?

The SELECT statement is used to select data from a database. The data returned is stored in a result table, sometimes called the result set.

Syntax of the SELECT Statement

The basic syntax of the SELECT statement is as follows:

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1SELECT column1, column2, ...
2FROM table_name;

• column1, column2, ... are the fields (columns) of the table you want to fetch data from.
• table_name is the name of the table from which you want to retrieve the data.

Selecting All Columns

To select all columns from a table, you can use the asterisk (*) wildcard character.

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1SELECT * FROM table_name;

This will return every column from every row in the table.

Selecting Specific Columns

To retrieve only the necessary data, specify the column names you want to select:

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1SELECT column1, column2 FROM table_name;

This will return only the data from column1 and column2.

Using Aliases

Aliases can be used to give a table or a column a temporary name. This is useful for improving readability or when you have multiple columns with the same name from different tables.

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1SELECT column_name AS alias_name FROM table_name;

For example:

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1SELECT first_name AS FirstName, last_name AS LastName FROM employees;

Filtering Results with WHERE

The SELECT statement can be combined with a WHERE clause to filter the results based on a condition.

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1SELECT column1, column2 FROM table_name WHERE condition;

For example:

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1SELECT FirstName, LastName FROM employees WHERE Department = 'Sales';

Sorting Results with ORDER BY

You can sort the result set by one or more columns using the ORDER BY clause. The default sorting order is ascending (ASC). To sort in descending order, use the DESC keyword.

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1SELECT column1, column2 FROM table_name ORDER BY column1 ASC, column2 DESC;

For example:

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1SELECT FirstName, LastName FROM employees ORDER BY LastName ASC;

Limiting Results with LIMIT

To limit the number of rows returned by a query, you can use the LIMIT clause.

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1SELECT column1, column2 FROM table_name LIMIT number;

For example, to get only the first 10 rows:

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1SELECT * FROM employees LIMIT 10;

Combining Columns with Concatenation

You can combine column values into a single column using the concatenation operator (|| in some databases like PostgreSQL or CONCAT() function in others like MySQL).

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1SELECT CONCAT(column1, ' ', column2) AS full_name FROM table_name;

For example:

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1SELECT CONCAT(FirstName, ' ', LastName) AS FullName FROM employees;

Distinct Values

To get distinct values from a column, use the DISTINCT keyword.

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1SELECT DISTINCT column1 FROM table_name;

For example:

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1SELECT DISTINCT Department FROM employees;

The SELECT statement is a powerful tool in SQL for retrieving data from a database. By specifying columns, using aliases, filtering with conditions, sorting, limiting, concatenating values, and selecting distinct entries, you can manipulate the result set to meet your requirements.