SELECT

The SELECT statement retrieves data from one or more tables.

Basic Syntax

SELECT [DISTINCT] column1, column2, ...
FROM table_name
[WHERE condition]
[GROUP BY column1, ... | ROLLUP(column1, ...) | CUBE(column1, ...)]
[HAVING condition]
[ORDER BY column1 [ASC|DESC] [NULLS FIRST|NULLS LAST], ...]
[LIMIT count [OFFSET offset]]

Parameters

• DISTINCT: Removes duplicate rows from the result
• column1, column2, …: Columns to retrieve; use * for all columns
• table_name: The table to query
• WHERE condition: Filter condition
• GROUP BY: Groups rows by specified columns
• ROLLUP/CUBE: Multi-dimensional aggregation (see ROLLUP and CUBE)
• HAVING: Filter applied to groups
• ORDER BY: Sorting of results (NULLS FIRST or NULLS LAST to control NULL placement)
• LIMIT: Maximum rows to return
• OFFSET: Number of rows to skip

Examples

-- Basic query
SELECT id, name, price FROM products;

-- Filtering
SELECT * FROM products WHERE price > 50.00 AND category = 'Electronics';

-- Sorting
SELECT * FROM products ORDER BY price DESC, name ASC;

-- Pagination
SELECT * FROM customers LIMIT 10 OFFSET 20;

-- Unique values
SELECT DISTINCT category FROM products;

-- Aggregation
SELECT category, AVG(price) AS avg_price, COUNT(*) as count
FROM products
GROUP BY category;

-- Filtering groups
SELECT category, COUNT(*) AS product_count
FROM products
GROUP BY category
HAVING COUNT(*) > 5;

JOIN Operations

Oxibase supports all standard JOIN types:

-- INNER JOIN
SELECT p.name, c.name AS category
FROM products p
INNER JOIN categories c ON p.category_id = c.id;

-- LEFT JOIN
SELECT c.name, o.id AS order_id
FROM customers c
LEFT JOIN orders o ON c.id = o.customer_id;

-- RIGHT JOIN
SELECT c.name, o.id AS order_id
FROM customers c
RIGHT JOIN orders o ON c.id = o.customer_id;

-- FULL OUTER JOIN
SELECT c.name, o.id
FROM customers c
FULL OUTER JOIN orders o ON c.id = o.customer_id;

-- CROSS JOIN
SELECT p.name, c.name
FROM products p
CROSS JOIN colors c;

See JOIN Operations for detailed documentation.

Subqueries

Using subqueries in various clauses (both correlated and non-correlated):

-- Scalar subquery
SELECT name, price,
       (SELECT AVG(price) FROM products) as avg_price
FROM products;

-- IN subquery
SELECT * FROM customers
WHERE id IN (SELECT DISTINCT customer_id FROM orders);

-- EXISTS subquery (correlated)
SELECT * FROM customers c
WHERE EXISTS (SELECT 1 FROM orders o WHERE o.customer_id = c.id);

-- NOT IN subquery
SELECT * FROM products
WHERE id NOT IN (SELECT product_id FROM discontinued_items);

-- Correlated subquery in WHERE
SELECT * FROM employees e1
WHERE salary > (SELECT AVG(salary) FROM employees e2 WHERE e2.department = e1.department);

-- ANY/ALL subquery
SELECT * FROM products WHERE price > ALL (SELECT price FROM products WHERE category = 'Books');

-- Derived table (subquery in FROM)
SELECT * FROM (SELECT id, name FROM products WHERE price > 100) AS expensive;

See Subqueries for detailed documentation.

Common Table Expressions (CTEs)

-- Simple CTE
WITH high_value_orders AS (
    SELECT * FROM orders WHERE total > 1000
)
SELECT * FROM high_value_orders;

-- Multiple CTEs
WITH
customer_totals AS (
    SELECT customer_id, SUM(total) as total_spent
    FROM orders
    GROUP BY customer_id
),
vip_customers AS (
    SELECT * FROM customer_totals WHERE total_spent > 10000
)
SELECT c.name, ct.total_spent
FROM customers c
JOIN vip_customers ct ON c.id = ct.customer_id;

-- Recursive CTE
WITH RECURSIVE numbers AS (
    SELECT 1 as n
    UNION ALL
    SELECT n + 1 FROM numbers WHERE n < 10
)
SELECT * FROM numbers;

See Common Table Expressions for detailed documentation.

Set Operations

-- UNION (removes duplicates)
SELECT name FROM customers
UNION
SELECT name FROM suppliers;

-- UNION ALL (keeps duplicates)
SELECT name FROM customers
UNION ALL
SELECT name FROM suppliers;

-- INTERSECT
SELECT id FROM table1
INTERSECT
SELECT id FROM table2;

-- EXCEPT
SELECT id FROM table1
EXCEPT
SELECT id FROM table2;

Temporal Queries (AS OF)

Query historical data at a specific point in time:

-- Query data as of a specific timestamp
SELECT * FROM orders AS OF TIMESTAMP '2024-01-15 10:30:00';

-- Query data as of current time
SELECT * FROM inventory AS OF TIMESTAMP NOW();

See Temporal Queries for detailed documentation.