SQL SELECT

What is the SQL SELECT statement?

SELECT retrieves data from one or more tables or views and returns it as a result set.

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Compatible dialects for SQL SELECT:

SQL SELECT Full Explanation

SELECT is the cornerstone of SQL and the primary means of reading data. A SELECT statement creates a virtual table (the result set) by projecting columns, filtering rows, joining related tables, grouping aggregates, ordering results, and optionally limiting the number of rows returned. It never modifies data. Because most database optimizers focus heavily on SELECT, understanding its clauses helps you write performant queries. The logical processing order is FROM, WHERE, GROUP BY, HAVING, SELECT, DISTINCT, ORDER BY, LIMIT-OFFSET, though the written order differs. Some dialects add proprietary extensions such as TOP (SQL Server) or QUALIFY (Snowflake). You can nest SELECT inside subqueries and common table expressions (CTEs) to build complex analyses. Caveats: omitting a WHERE clause selects all rows, NULLs require special handling with IS NULL, and non-aggregated columns must appear in GROUP BY unless the dialect supports functional dependency shortcuts (e.g., MySQL ONLY_FULL_GROUP_BY disabled).

SQL SELECT Syntax

SELECT [ALL | DISTINCT] column1, column2, ...
FROM table_expression
[WHERE condition]
[GROUP BY column_list]
[HAVING condition]
[ORDER BY column_list [ASC | DESC]]
[LIMIT count] [OFFSET start];

SQL SELECT Parameters

column_list (list) - One or more columns or expressions to return.
table_expression (table/view/cte) - Source data set; may include JOINs or subqueries.
WHERE condition (boolean) - Row-level filter applied before grouping.
GROUP BY column_list (list) - Columns that define aggregation groups.
HAVING condition (boolean) - Filter applied after aggregation.
ORDER BY column_list (list) - Defines sort order of the result.
LIMIT count (integer) - Maximum number of rows to return (not in all dialects).
OFFSET start (integer) - Rows to skip before returning results.
DISTINCT (keyword) - Removes duplicate rows from the projection.
ALL (keyword) - Returns all rows, including duplicates (default).

Example Queries Using SQL SELECT

-- 1. Basic read
SELECT *
FROM users;

-- 2. Filter and sort
SELECT id, name, created_at
FROM users
WHERE active = true
ORDER BY created_at DESC
LIMIT 20;

-- 3. Aggregate with grouping
SELECT department_id, COUNT(*) AS headcount
FROM employees
WHERE active = true
GROUP BY department_id
HAVING COUNT(*) > 5;

-- 4. Join two tables
SELECT o.id, o.total, c.company_name
FROM orders o
JOIN customers c ON c.id = o.customer_id
WHERE o.status = 'shipped';

Expected Output Using SQL SELECT

The database engine returns a result set consisting of zero or more rows and the requested columns, optionally containing aggregated values, sorted and limited as specified

Use Cases with SQL SELECT

Reading data for application features
Building analytics and dashboards
Validating ETL results
Feeding reports or APIs with live data
Rapid ad-hoc exploration in an editor like Galaxy

Common Mistakes with SQL SELECT

Forgetting WHERE and unintentionally selecting every row
Referencing non-aggregated columns in SELECT without listing them in GROUP BY
Assuming ORDER BY without LIMIT is inexpensive on large tables
Using SELECT * in production code, causing brittle queries and excess I/O
Misusing DISTINCT to remove duplicates that should be handled by better modeling

First Introduced In

ANSI SQL-86 (X3.135-1986)

Frequently Asked Questions

What does SQL SELECT return?

It returns a result set - a virtual table of rows and columns that match the query conditions.

Can I use SELECT without FROM?

Yes in some dialects. For example, `SELECT 1;` returns a single row with the value 1, useful for quick calculations or health checks.

How do DISTINCT and GROUP BY differ?

DISTINCT removes duplicate rows across all selected columns, while GROUP BY collapses rows into groups so you can apply aggregate functions like COUNT or SUM.

Why is my SELECT query slow?

Common causes include missing indexes on filtered or joined columns, returning too many rows, or sorting large result sets without supporting indexes.