Database and SQL

What Is a Relational Database? Organizing Data in Tables A database is an organized collection of data. A relational database stores that data in tables, which look like ...

Installing MySQL and Your First Queries Getting MySQL Running MySQL is one of the most popular open-source relational databases. To begin, download MySQL Community Server from the ...

Database Design and Normalization Design Before Data How you structure tables determines how easy the database is to maintain and query. Good design starts with understanding the ...

CREATE TABLE and Data Types Talking to the Database The CREATE TABLE statement defines a table, its columns, data types, and constraints. Choosing the right types and constraints ...

Writing Data: INSERT, UPDATE, DELETE Adding Rows with INSERT Queries that read data are half the story. To store new records you use INSERT, to modify them UPDATE, and to remove ...

Reading Data: SELECT and Filtering The Basic Query SELECT is the workhorse of SQL. Its simplest form picks columns from a table: The asterisk returns every column (SELECT * FROM ...

Joins: Connecting Tables Why Joins Exist Relational design spreads facts across tables: customers in one table, orders in another. To answer a question that touches both, you join ...

Aggregate Functions and GROUP BY Summarizing Data Sometimes you do not want every row, but a summary: the average price, the number of orders, the biggest sale. Aggregate ...

Indexes and Query Performance Why Small Tables Are Fast and Big Ones Are Not A table with a million rows scans slowly if every query has to inspect every row. An index is a sorted ...

Transactions and ACID When One Step Is Not Enough Some operations touch several rows and must succeed or fail as a unit. Transferring money between two accounts updates two ...