Introduction to T-SQL

T-SQL (Transact-SQL) is Microsoft's extension of SQL used in SQL Server and Azure SQL Database, adding procedural programming features like variables, loops, and error handling on top of standard SQL.

SQL vs T-SQL

Standard SQL (Structured Query Language) lets you query and manipulate relational data with commands like SELECT, INSERT, and UPDATE. T-SQL builds on this foundation with Microsoft-specific extensions — variables, control-of-flow statements, stored procedures, and built-in functions — that turn SQL from a purely declarative query language into something closer to a full programming environment for the database.

T-SQL runs on Microsoft SQL Server and Azure SQL Database, and is one of the most widely used database skills in corporate and enterprise environments worldwide.

A First Query

Almost every T-SQL statement you write revolves around tables — structured collections of rows and columns. Here's a first look at retrieving data from one.

SELECT FirstName, LastName, Email
FROM Customers;

Common Mistakes

• Assuming all SQL dialects are identical — T-SQL, MySQL, and PostgreSQL each have their own extensions and quirks.
• Forgetting the semicolon at the end of statements, which SQL Server tolerates for single statements but is required by the standard and good practice for clarity.
• Confusing a database (a container) with a table (a structured collection of data inside it).
• Not knowing which database you're connected to before running a query, especially in an environment with multiple databases.