How to Use the SELECT Statement in MariaDB

How do I use the SELECT statement in MariaDB to retrieve and filter data?

SELECT retrieves rows and columns from one or more MariaDB tables based on optional filtering, sorting, grouping, and limiting clauses.

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Description

Example H2

Example H3

What is the purpose of SELECT in MariaDB?

SELECT returns data stored in tables. You can fetch every column or only the fields you need, apply conditions, join tables, aggregate results, and order or limit the output.

How do I select specific columns?

List the column names after SELECT. Example: SELECT id, name, email FROM Customers; This reduces network traffic and speeds up queries.

How can I filter rows with WHERE?

Attach a WHERE clause.Example: SELECT * FROM Orders WHERE total_amount > 100; Use comparison, BETWEEN, IN, LIKE, IS NULL, and logical operators.

How do I join multiple tables?

Use INNER JOIN (default), LEFT JOIN, RIGHT JOIN, or CROSS JOIN. Example: SELECT c.name, o.order_date FROM Customers c JOIN Orders o ON c.id = o.customer_id;

When should I aggregate with GROUP BY?

Apply GROUP BY with aggregate functions to summarize data.Example: SELECT customer_id, SUM(total_amount) AS lifetime_spend FROM Orders GROUP BY customer_id;

How do I sort and limit results?

ORDER BY arranges rows; LIMIT restricts row count. Example: SELECT * FROM Products ORDER BY price DESC LIMIT 5;

What are best practices for SELECT?

Always specify columns, filter early, index filter columns, avoid SELECT *, test LIMIT before heavy queries, and analyze EXPLAIN plans.

Can I use subqueries and CTEs?

Yes.Subquery example: SELECT name FROM Products WHERE id IN (SELECT product_id FROM OrderItems WHERE quantity > 10); CTE example (MariaDB 10.2+): WITH high_value AS (SELECT id FROM Orders WHERE total_amount > 500) SELECT * FROM high_value;

Real-world scenario

Fetch the five most expensive items ever ordered, with buyer email: SELECT p.name, p.price, c.email FROM OrderItems oi JOIN Products p ON oi.product_id = p.id JOIN Orders o ON oi.order_id = o.id JOIN Customers c ON o.customer_id = c.id ORDER BY p.price DESC LIMIT 5;

Why How to Use the SELECT Statement in MariaDB is important

How to Use the SELECT Statement in MariaDB Example Usage


-- Top 3 customers by lifetime spend
SELECT c.id,
       c.name,
       SUM(o.total_amount) AS lifetime_spend
FROM   Customers c
JOIN   Orders o ON o.customer_id = c.id
GROUP  BY c.id, c.name
ORDER  BY lifetime_spend DESC
LIMIT  3;

How to Use the SELECT Statement in MariaDB Syntax


SELECT [ALL | DISTINCT]
       select_expr [, select_expr ...]
FROM   table_reference
       [JOIN type JOIN table_reference ON join_condition ...]
[WHERE  condition]
[GROUP BY expr [, expr ...]]
[HAVING group_condition]
[ORDER BY expr [ASC|DESC] [, expr ...]]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]

-- Ecommerce-oriented example
SELECT c.name,
       o.order_date,
       o.total_amount
FROM   Customers AS c
JOIN   Orders    AS o ON o.customer_id = c.id
WHERE  o.order_date >= '2024-01-01'
ORDER BY o.total_amount DESC;

Common Mistakes

Using SELECT * in production queries. This returns unnecessary columns, increases network usage, and breaks apps if schema changes. Fix: list required columns explicitly.
Forgetting indexes on columns used in WHERE or JOIN conditions. This causes full table scans and slow queries. Fix: add appropriate indexes and analyze with EXPLAIN.