Coding is always a fun but challenging job. Developers do not only have to execute the right output based on the business requirement but also need to maintain the right coding standards by using the optimum use of variable sizes and keeping in view the other best practices. I am going to provide a list of best practices and guidelines today, in this article. Many of us already may have been using these but I thought to gather those in a single page so that while developing, the code can be useful, keeping the standard intact.
Application to be used,

• Developers need to use the Developer Edition of the SQL Server edition rather than using SQL Express or Enterprise edition.

Database Design

• Ensure that the referential integrity is maintained at all the times, i.e., the relationship between Primary Key and Foreign Key.

• Always specify the narrowest columns you can. In addition, always choose the smallest data type you need to hold the data you need to store in a column. The narrower the column, the less amount of data SQL Server must store, and the faster SQL Server is able to read and write data.

Database Configuration Settings

• Create proper database file sizes (this includes Initial DB file size and growth values)
• Maintaining consistency in DB filegroups across the markets.

Data modeling

• Use of appropriate data types and length while the data models are created (limit using blob data types unless really needed). The narrower the column, the less amount of data SQL Server must store, and the faster SQL Server is able to read and write data.

Performance/Load Tests

• While performing perf tests, adjusts the database file sizes accordingly. Suspend the maintenance jobs during the period.

Purging solution

• Checking with the business team over a period to implement the correct data purging solutions which best fits your environment.

Database Objects

• Use user-defined constraint names rather using system-generated names.
• Use database objects to sit in the respective defined Filegroups. Avoid getting the user objects and data to sit in the system/primary filegroup.

Indexing

• Appropriate Index Naming convention.
• Appropriate use of Case while creating objects such as tables, indexes and other objects.
• Use the appropriate column sequence while creating the index schema.
• Try to avoid creating duplicate indexes.
• Limit use of filtered indexes unless you are sure that can give you real benefits.
• When creating a composite index, and when all other considerations are equal, make the most selective column in the first column of the index.
• keep the “width” of your indexes as narrow as possible. This reduces the size of the index and reduces the number of disks I/O reads required to read the index, boosting performance.
• Avoid adding a clustered index to a GUID column (unique identifier data type). GUIDs take up 16-bytes of storage, more than an Identify column, which makes the index larger, which increases I/O reads, which can hurt performance.
• Indexes should be considered on all columns that are frequently accessed by the JOIN, WHERE, ORDER BY, GROUP BY, TOP, and DISTINCT clauses.
• Don't automatically add indexes on a table because it seems like the right thing to do. Only add indexes if you know that they will be used by queries run against the table. Always assess your workload before creating the right indexes.
• When creating indexes, try to make them unique indexes if possible. SQL Server can often search through a unique index faster than a non-unique index because in a unique index, each row is unique, and once the needed record is found, SQL Server doesn't have to look any further.

Properties of Indexes

• Don’t automatically accept the default value of 100 for the fill factor for your indexes. It may or may not best meet your needs. A high fill factor is good for seldom changed data, but highly modified data needs a lower fill factor to reduce page splitting.

Transact-SQL

• If you perform regular joins between two or more tables in your queries, performance will be optimized if each of the joined columns has appropriate indexes.
• Don't over-index your OLTP tables, as every index you add increases the time it takes to perform INSERTS, UPDATES, and DELETES. There is a fine line between having the ideal number of indexes (for SELECTs) and the ideal number to minimize the overhead that occurs with indexes during data modifications.
• If you know that your application will be performing the same query over and over on the same table, consider creating a non-clustered covering index on the table. A covering index, which is a form of a composite index, includes all the columns referenced in SELECT, JOIN, and WHERE clauses of a query. Because of this, the index contains the data you are looking for and SQL Server doesn't have to look up the actual data in the table, reducing I/O, and boosting performance.
• Remove encryption from table columns where it is not necessary at all. Overuse of encryption can lead to poor performance. Check with business users time to time on this to ensure right table columns are only considered for encryption.

Version control/source control

• Maintain all code in a source control system and update it always for all type of changes happening to the code base.

Queries and Stored Procedures

• Keep the transactions as short as possible. This reduces locking and increases the application concurrency, which helps to boost the performance.
• If needed to run SQL commands use only designated columns rather using * to fetch all the commands and use the TOP operator to limit the number of records.
• Avoid using query hints unless you know exactly what you are doing, and you have verified that the hint boosts performance. Instead, use the right isolation levels.
• SET NOCOUNT ON at the beginning of each stored procedure you write.
• Do not unnecessarily use select statements in the code block if you do not want to send any result back to display.
• Avoid such code which can lead to unnecessary network calls. Check the count of the code block and verify if those many calls are really needed.
• When using the UNION statement, keep in mind that, by default, it performs the equivalent of a SELECT DISTINCT on the result set. In other words, UNION takes the results of two like record sets, combines them, and then performs a SELECT DISTINCT in order to eliminate any duplicate rows. This process occurs even if there are no duplicate records in the final recordset. If you know that there are duplicate records, and this presents a problem for your application, then use the UNION statement to eliminate the duplicate rows.
• If you see there is a necessity to use Upper () or Lower () functions or need to use LTRIM () or RTRIM () functions, it will be better to modify the data corrected while accepting the user inputs from the application side rather performing changes in the script. This will make the queries to run faster.
• Carefully evaluate whether your SELECT query needs the DISTINCT clause or not. Some developers automatically add this clause to every one of their SELECT statements, even when it is not necessary.
• In your queries, don't return column data you don't need. For example, you should not use SELECT * to return all the columns from a table if you don't need all the data from every column. In addition, using SELECT * may prevent the use of covering indexes, further potentially hurting query performance.
• Always include a WHERE clause in your SELECT statement to narrow the number of rows returned. Only return those rows you need.
• If your application allows users to run queries, but you are unable in your application to easily prevent users from returning hundreds, even thousands of unnecessary rows of data, consider using the TOP operator within the SELECT statement. This way, you can limit how many rows are returned, even if the user doesn't enter any criteria to help reduce the number of rows returned to the client.
• Try to avoid WHERE clauses that are non-sargable. If a WHERE clause is sargable, this means that it can take advantage of an index (assuming one is available) to speed completion of the query. If a WHERE clause is non-sargable, this means that the WHERE clause (or at least part of it) cannot take advantage of an index, instead of performing a table/index scan, which may cause the query's performance to suffer. Non-sargable search arguments in the WHERE clause, such as "IS NULL", "<>", "!=", "!>", "!<", "NOT", "NOT EXISTS", "NOT IN", "NOT LIKE", and "LIKE '%500'" generally prevents (but not always) the query optimizer from using an index to perform a search. In addition, expressions that include a function on a column, expressions that have the same column on both sides of the operator, or comparisons against a column (not a constant), are not sargable. In such case, break the code appropriately so that a proper index or set of indexes can be used.
• If using temporary tables to keep the backup of the existing large tables in the database, remove them as and when the task is needed as those contain a lot of storage and the maintenance plan will take more time to complete as because those tables will be considered for maintenance as well.
• Do not use special characters or use them very carefully while passing them via a stored procedure. It might change the query execution plan and lead to poor performance. Often the situation is known as Parameter sniffing.
• Avoid SQL server to do an implicit conversion of data, rather use it appropriately (use explicit code-based conversion).

SQL Server CLR
The Common language runtime (CLR) feature allows you to write stored procedures/trigger/functions in .NET managed code and execute the same from SQL Server.

• Use the CLR to complement Transact-SQL code, not to replace it.
• Standard data access, such as SELECT, INSERTs, UPDATEs, and DELETEs are best done via Transact-SQL code, not the CLR.
• Computationally or procedurally intensive business logic can often be encapsulated as functions running in the CLR.
• Use CLR for error handling, as it is more robust than what Transact-SQL offers.
• Use CLR for string manipulation, as it is generally faster than using Transact-SQL.
• Use CLR when you need to take advantage of the large base class library.
• Use CLR when you want to access external resources, such as the file system, Event Log, a web service, or the registry.
• Set CLR code access security to the most restrictive permissions as possible.

Consultation

• You can also a consultant with your in-house DBAs for any advice about Microsoft Best Practices and standard or use of correct indexes to be used.
• You can seek training from any good external training providers.
• Another good option is to use good third-party tools such as RedGate, FogLight, Idera, SQLSentry, SolarWinds and check the performance of the environment by monitoring the scripts.

Process Improvement

• Document common mistakes in the Lessoned Learned page per the PMP best practice guidelines.
• Do check out the new upcoming editions and try to align your code accordingly.

Hope that the above-advised guidelines would be useful. Do share if you use any other steps in your workplace which is found to be helpful.

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