PostgreSQL: Selecting Data with the SELECT Command

Retrieve data from PostgreSQL tables using the SELECT command. This guide covers basic syntax, clauses, and examples for various data retrieval tasks.

Selecting Data in PostgreSQL Using the `SELECT` Command

In PostgreSQL, the `SELECT` command is fundamental for retrieving data from database tables. This guide covers the basic syntax, various clauses, and examples of how to use `SELECT` for different data retrieval tasks.

Basic `SELECT` Syntax

SELECT select_list FROM table_name;

This retrieves data from a table. The `select_list` specifies which columns to retrieve (you can list individual column names separated by commas, or use `*` to select all columns). `table_name` specifies the table from which data is retrieved. PostgreSQL is not case sensitive (e.g., `SELECT` and `select` are equivalent).

Specifying Columns to Retrieve

You can select specific columns:

SELECT column1, column2, column3 FROM my_table;

Or select all columns using an asterisk (`*`):

SELECT * FROM my_table;

While the `*` syntax is convenient, it's generally better to explicitly list the columns you need for better readability, maintainability, and to avoid transferring unnecessary data.

Example 1: Selecting Data from a Single Column

(Note: This assumes a table named "Company"."employee" exists with a column named "name". Screenshots from the original text are not included here. Please refer to the original document for visual verification of the output. The description below aims to convey the information present in the screenshot.)

SELECT name FROM "Company"."employee";

Example 2: Selecting Multiple Columns

(Note: This assumes a table named "Company"."employee" exists with columns "name", "age", and "address".)

SELECT name, age, address FROM "Company"."employee";

Example 3: Selecting All Columns

(Note: This assumes a table named "Company"."employee" exists.)

SELECT * FROM "Company"."employee";

Using Expressions in the `SELECT` Clause

You can use expressions (calculations, functions) in your `SELECT` statement:

SELECT name || ' ' || surname AS full_name FROM employees;

This example concatenates the `name` and `surname` columns and aliases the result as `full_name`.

`SELECT` Without `FROM`

You can use `SELECT` without a `FROM` clause to return literal values:

SELECT 10 * 5 AS result;