PostgreSQL Select

The SELECT Statement

A SELECT statement names the columns you want and the table to read them from. PostgreSQL executes the FROM clause first internally, then applies any filtering, and finally projects only the columns you listed. Column names are separated by commas, and the statement ends with a semicolon.

SELECT name, department, salary
FROM employees;

Selecting All Columns

The asterisk (*) is shorthand for every column in the table, in the order they were defined. It's convenient while exploring data interactively, but it returns columns you may not need and breaks if the table's shape changes later.

Aliases and Computed Columns

SELECT isn't limited to raw column names. You can rename output columns with AS, combine columns with expressions, call functions, and concatenate text, all within the same list. An alias only renames the result set; it never changes the underlying table.

SELECT name,
       salary AS annual_salary,
       salary / 12 AS monthly_salary
FROM employees;

• AS renames a column or expression in the result set
• Arithmetic expressions (salary / 12) can appear directly in the column list
• String concatenation uses the || operator, e.g. first_name || ' ' || last_name
• Function calls like UPPER(name) can be used anywhere a column can

SELECT DISTINCT department
FROM employees;