Be sure to use the join syntax. Pick the join order carefully. The majority of outer joins can successfully be rewritten as inner joins with tremendous performance improvements. This is a coding best practice that leads to more maintainable code and database systems. Null Comparisons Database SQL developers, check stored procedures, views, functions and triggers to flag the use of equality and inequality comparisons involving a NULL constant.
Avoid using this feature in new development work, and plan to modify applications that currently use this feature. It is recommended to use quoted identifiers instead. String aliases are not supported in future releases of SQL Server. Tables without a Primary Key defined or a column with a unique constraint defined will not be approved. Foreign keys are also defined as indexes. Database Administrators check stored procedures, functions, views and triggers for use of schema qualified names when referencing tables and views.
However, it is recommended that at least the schema name be specified to identify a table or view inside a stored procedure, function, view or trigger. In either case, SQL Server incurs an additional runtime cost to verify schema binding of unqualified objects. Applications are more maintainable and may experience a slight performance improvement if object references are schema qualified.
It is recommended to specify sort criteria when using TOP clause. Otherwise, the results produced are plan dependent and may lead to undesired behaviour. Avoid Stored Procedure Recompiles Performance Recommendations General Considerations Stored procedures perform one process and not a series of processes. It is better to create a stored procedure that performs an insert rather than a stored procedure that performs an insert, update and a delete.
Executing multiple stored procedures is preferred over executing one, unwieldy, multi-task stored procedure. If data operations are mixed, the SQL server must recompile procedures each time to determine the best plan to use for each new or dropped object.
Therefore, coding all creates and drops together reduces the amount of stored procedure compiles. Avoid using a DROP statement for temporary tables in stored procedures, because tables are automatically dropped when the procedure is completed. Specifying the owner of objects such as dbo. Tablename and dbo. Stored procedure name cuts down on recompiles. Temporary Tables Often procedure throughput can be dramatically improved by the use of temporary tables.
Please note: use a temporary table to manipulate small amounts of data, and if data exceeds records add an index. Table Variable Type The table variable type functions exactly like the temporary table, with the exception that all data is loaded directly in random access memory. Temporary Tables vs. When a procedure creates a temporary table and has no CREATE INDEX issued on it, and it is dropped all in the same procedure, consider using table variables instead to potentially observe fewer recompilations.
Note that if large data volumes are inserted in the temporary table it may still be preferred to use temporary tables over table variables due to parallel execution restrictions and statistics maintenance.
Indexes Examine the performance of the statements within the procedure and the entire application to determine if an additional index will justify its overhead. Consider overall index usage all along the development path. Please note when setting an index, pay close attention to the fill factor for the given index.
The fill factor is the amount space consumed by the index and more importantly the amount of space that will be kept free for expansion. For tables that do a high volume of inserts, updates, deletes consider a lower fill factor, or perhaps not having a clustered index at all. A clustered index slows down inserts but speed up selects. The developer determines what the best trade-off is. Ultimately, it is the responsibility of the developer coding the stored procedures and the SQL code to determine what the best indexes are and how they are used.
Execution Plan When debugging and tuning a stored procedure, examine the execution plan for clues as to the performance of the procedure and how it may be improved.
The reason for execution plan is to determine whether an index is required. In the example below, execution identifies a missing index that could improve performance.
From this, one asks if another index should be created to avoid the scan. If yes, create an index and rerun. The SQL developer can analyse the output from these tools and give suggestions on what tables or objects have problems and can benefit from index creation.
Programmatic Recommendations This section provides recommendations to developers for improving the reliability of procedures and triggers. Stylistic Recommendations This section provides recommendations to SQL developers for improving the readability of procedures and triggers. Use compound Boolean expressions instead.
No more than 4 nested IF statements are allowed. In a development environment, the developer testing the package may own the package but in all other environments SA System Administrator owns the package.
The package may very well have the same name as the job. The difference between a job and a package is that a job is a scheduled package. A package on its own must be started manually. The package names can be mixed case for ease of readability.
The job name is the same name as the SSIS package. SA owns the job in all environments. Exercises at the end of each chapter let you practice the skills you learn. With this book, you will: Move quickly through SQL basics and learn several advanced features Use SQL data statements to generate, manipulate, and retrieve data Create database objects, such as tables, indexes, and constraints, using SQL schema statements Learn how data sets interact with queries, and understand the importance of subqueries Convert and manipulate data with SQL's built-in functions, and use conditional logic in data statements Knowledge of SQL is a must for interacting with data.
With Learning SQL, you'll quickly learn how to put the power and flexibility of this language to work. In order to build effective database applications, you must gain a thorough understanding of these features. This book provides you with a comprehensive introduction to the T-SQL language and shows you how it can be used to work with both the SQL Server and releases.
Beginning with an overview of the SQL Server query operations and tools that are used with T-SQL, the author goes on to explain how to design and build applications of increasing complexity.
By gaining an understanding of the power of the T-SQL language, you'll be prepared to meet the ever-increasing demands of programming. What you will learn from this book How T-SQL provides you with the means to create tools for managing hundreds of databases Various programming techniques that use views and stored procedures Ways to optimize query performance How to create databases that will be an essential foundation to applications you develop later Who this book is for This book is for database developers and administrators who have not yet programmed with Transact-SQL.
Some familiarity with relational databases and basic SQL is helpful, and some programming experience is helpful. Wrox Beginning guides are crafted to make learning programming languages and technologies easier than you think, providing a structured, tutorial format that will guide you through all the techniques involved.
Apply powerful window functions in T-SQL—and increase the performance and speed of your queries Optimize your queries—and obtain simple and elegant solutions to a variety of problems—using window functions in Transact-SQL.
Discover how to: Go beyond traditional query approaches to express set calculations more efficiently Delve into ordered set functions such as rank, distribution, and offset Implement hypothetical set and inverse distribution functions in standard SQL Use strategies for improving sequencing, paging, filtering, and pivoting Increase query speed using partitioning, ordering, and coverage indexing Apply new optimization iterators such as Window Spool Handle common issues such as running totals, intervals, medians, and gaps.
Work at your own pace through a series of lessons and practical exercises, and then assess your skills with practice tests on CD—featuring multiple, customizable testing options. Maximize your performance on the exam by learning how to: Create database objects Work with data Modify data Troubleshoot and optimize queries You also get an exam discount voucher—making this book an exceptional value and a great career investment.
T-SQL is the foundation for business logic embedded in the database in the form of stored procedures and functions. Beginning T-SQL starts you on the path to mastering T-SQL, with an emphasis on best-practices and sound coding techniques leading to excellent performance. Important techniques such as windowing functions are covered to help write fast executing queries that solve real business problems.
A stand-out feature in this book is that most chapters end with a "Thinking About Performance" section. These sections cover aspects of query performance relative to the content just presented. They'll help you avoid beginner mistakes by knowing about and thinking about performance from Day 1. Imparts best practices for writing T-SQL Helps you avoid common errors Shows how to write scalable code for good performance.
After reading this book, you will be able to create, modify, and delete databases, tables, and indexes. You can practice querying the data and running complex analytics on it. You will also be able to add, delete, and modify procedures, user-defined functions, triggers, and views. You'll then learn how to use DDL statements to create, modify and delete tables and indexes. Successively, you'll learn XML and JSON data processing, and by the time you'll reach the end of this book, you will learn to program in SQL Server and various strategies to deploy your databases and programs.
Throughout the book, you'll learn through simple examples and straightforward explanations, diagrams, and numerous real-world use-cases. Readers with a basic understanding of programming would have an advantage. Getting started 2. Tables 3. Index 4. DML 5. Built-In Functions - Part 1 6. Join, Apply, and Subquery 7. Built-In Functions - Part 2 8.
Variables and Control Flow Statements Error Handling and Transaction Management Programmability If so, you're in the right place! You will then focus on query execution plans and leverage them for troubleshooting. In later chapters, you will explain how to identify various T-SQL patterns and anti-patterns.
This will help you analyze execution plans to gain insights into current performance, and determine whether or not a query is scalable. Next, you will work with the built-in tools of SQL Server to shorten the time taken to address query performance and scalability issues.
In the concluding chapters, the book will guide you through implementing various features, such as Extended Events, Query Store, and Query Tuning Assistant, using hands-on examples.
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