What is T-SQL?
Transact-SQL (T-SQL) is an extension of SQL (Structured Query Language) used in Microsoft SQL Server and Sybase ASE. It includes procedural programming, local variables, and various support functions for string processing, date processing, mathematics, etc.
Basic Syntax
Here are some essential elements of T-SQL syntax:
SELECT Statement
Used to query data from a database:
SELECT column1, column2
FROM table_name
WHERE condition;
INSERT Statement
Used to insert new records into a table:
INSERT INTO table_name (column1, column2)
VALUES (value1, value2);
UPDATE Statement
Used to modify existing records in a table:
UPDATE table_name
SET column1 = value1, column2 = value2
WHERE condition;
DELETE Statement
Used to delete records from a table:
DELETE FROM table_name
WHERE condition;
Key Concepts
1. Data Types
Understanding data types is crucial for defining the type of data that can be stored in a column. Common data types include:
- INT: Integer data type.
- VARCHAR: Variable-length string.
- DATE: Date value.
- DECIMAL: Numeric data type with fixed precision and scale.
2. Functions
T-SQL includes a variety of built-in functions to perform operations on data:
- GETDATE(): Returns the current date and time.
- LEN(): Returns the length of a string.
- SUBSTRING(): Extracts a substring from a string.
- CONVERT(): Converts a value from one data type to another.
3. Joins
Joins are used to combine rows from two or more tables based on a related column:
- INNER JOIN: Returns records that have matching values in both tables.
- LEFT JOIN: Returns all records from the left table and matched records from the right table.
- RIGHT JOIN: Returns all records from the right table and matched records from the left table.
- FULL JOIN: Returns all records when there is a match in either left or right table.
SELECT a.column1, b.column2
FROM table1 a
INNER JOIN table2 b ON a.common_field = b.common_field;
Best Practices
- Use meaningful and descriptive names for tables and columns.
- Always include a WHERE clause with UPDATE and DELETE statements to avoid unintentional changes.
- Use comments to document your code for better readability and maintenance.
- Normalize your database to reduce redundancy and improve data integrity.
- Regularly back up your database to prevent data loss.
Resources
For further learning, consider the following resources:
