T-SQL Language Elements - MSDN Documentation

Transact-SQL (T-SQL) is Microsoft's proprietary extension of the SQL standard. It is used for querying and managing databases in Microsoft SQL Server. T-SQL enhances SQL with procedural programming, local variables, various support functions for data manipulation, and extended programming constructs.

Understanding the fundamental building blocks of T-SQL is crucial for effective database development and administration. This section provides an overview of the core language elements that form the basis of all T-SQL statements and scripts.

Key Language Elements

Identifiers

Identifiers are the names used to refer to database objects such as tables, views, columns, stored procedures, functions, and more. They must follow specific rules regarding characters, length, and uniqueness within their scope. T-SQL supports both regular and delimited identifiers.

Example of a regular identifier:

CustomerOrders

Example of a delimited identifier (useful for names with spaces or reserved keywords):

[Customer Orders]

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Literals

Literals are constant values that are directly represented in source code. T-SQL supports various types of literals, including character literals (strings), numeric literals, date and time literals, and bit literals.

Examples:

'Hello, World!'

123.45

GETDATE() -- Not a literal, but a function call returning a date/time value

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Keywords

Keywords are predefined words that have special meaning in T-SQL and cannot be used as identifiers unless they are delimited. Examples include SELECT, FROM, WHERE, CREATE, ALTER, DELETE, INSERT, UPDATE, and IF.

Example using keywords:

SELECT Column1, Column2 
FROM YourTable 
WHERE Column1 = 'SomeValue';

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Comments

Comments are non-executing parts of T-SQL code used for documentation, explanation, or temporarily disabling code. T-SQL supports two types of comments: single-line comments using double hyphens (--) and multi-line comments enclosed in /* ... */.

Example of single-line comment:

-- This is a single-line comment.

Example of multi-line comment:

/*
               This is a
               multi-line comment
               explaining the code below.
            */

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Operators

Operators are special symbols or keywords that perform operations on one or more operands. T-SQL includes arithmetic operators, string concatenation operators, comparison operators, logical operators, bitwise operators, and assignment operators.

Common examples:

Arithmetic: +, -, *, /, %
Comparison: =, <>, >, <, >=, <=
Logical: AND, OR, NOT

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Structure of T-SQL Statements

T-SQL statements are typically structured to perform specific database operations. The most common statement, SELECT, retrieves data and follows a general structure:

SELECT column_list
FROM table_name
[WHERE conditions]
[GROUP BY column_list]
[HAVING conditions]
[ORDER BY column_list];

Other T-SQL statements, such as INSERT, UPDATE, DELETE (Data Manipulation Language - DML), and CREATE, ALTER, DROP (Data Definition Language - DDL), have their own syntax and structure.

Putting It All Together

By combining identifiers, literals, keywords, and operators within well-formed statements and control-flow structures (like IF...ELSE and WHILE), developers can create complex and powerful database solutions using T-SQL.

This overview serves as a starting point. Each element is detailed further in its respective documentation section.

SQL Server T-SQL

T-SQL Language Elements Overview