Учебные материалы по SQL

Explore the different methods for filtering out and permanently removing duplicate rows using SQL. Learn the practical applications of how to remove duplicates in SQL Server, MySQL, and PostgreSQL.

Discover how WHERE filters row-level data in SQL queries, while HAVING filters grouped data after aggregation, and master their distinct uses in SQL querying.

Understand the SQL order of execution and how its different from the order of writing. Write accurate and optimized queries for improved performance and avoid common mistakes in query design.

A transitive dependency occurs when one attribute in a database indirectly relies on another through a third attribute, causing redundancy. Keep reading to learn how to identify and eliminate transitive dependencies in database design .

Learn how UPDATE with JOIN in SQL simplifies cross-table updates in SQL Server. Understand how INNER JOIN and LEFT JOIN differ for specific use cases, and explore alternatives using subqueries or the MERGE statement.

Explore how using a SQL alias simplifies both column and table names. Learn why using a SQL alias is key for improving readability and managing complex joins.

LEFT JOIN and LEFT OUTER JOIN in SQL are identical, with no functional difference between them. Keep reading to explore practical examples and discover how to apply these joins effectively in your queries.

The SQL OR operator allows you to filter data by combining multiple conditions, returning rows where at least one condition is true. Learn how to use OR with INSERT, UPDATE, and DELETE statements to modify records in tables.

Learn how to use SQL triggers to automate tasks, maintain data integrity, and enhance database performance. Try practical examples like the CREATE, ALTER, and DROP commands in MySQL and Oracle.

Learn how to use DECODE() in Oracle for conditional logic in data transformation. Compare DECODE() to the CASE WHEN statement in performance and behavior.

Discover how OLAP (Online Analytical Processing) enhances data analysis by providing rapid, multidimensional exploration for informed business decision-making.

Enhance your SQL skills with the SQL PIVOT operator. Learn to convert rows into columns to create pivot tables in SQL Server and Oracle.