Writing Basic SQL Queries

Introduction

SQL (Structured Query Language) is the standard language for managing and manipulating databases. This lesson covers the fundamentals of writing basic SQL queries to interact with databases.

Basic SQL Commands

In SQL, you can perform various operations using different commands. Here are some of the essential SQL commands:

1. SELECT

The SELECT statement is used to retrieve data from a database.

SELECT column1, column2
FROM table_name;

2. INSERT

The INSERT INTO statement is used to add new rows to a table.

INSERT INTO table_name (column1, column2)
VALUES (value1, value2);

3. UPDATE

The UPDATE statement is used to modify existing data in a table.

UPDATE table_name
SET column1 = value1
WHERE condition;

4. DELETE

The DELETE statement is used to remove rows from a table.

DELETE FROM table_name
WHERE condition;

5. WHERE Clause

The WHERE clause is used to filter records.

SELECT column1, column2
FROM table_name
WHERE condition;

6. ORDER BY

The ORDER BY clause is used to sort the result set.

SELECT column1, column2
FROM table_name
ORDER BY column1 ASC;

7. JOINs

JOIN operations are used to combine rows from two or more tables based on a related column.

SELECT columns
FROM table1
JOIN table2 ON table1.common_column = table2.common_column;

8. Aggregate Functions

Aggregate functions perform a calculation on a set of values and return a single value. Common aggregate functions include COUNT(), SUM(), AVG(), MIN(), and MAX().

SELECT COUNT(*)
FROM table_name;

Best Practices

• Use meaningful table and column names for clarity.
• Always specify the columns you need instead of using *.
• Use WHERE clauses to limit the result set.
• Be cautious with DELETE and UPDATE; always back up data.
• Use comments in your SQL code for documentation purposes.