Gogula G. Aryalingamhttp://dbantics.wordpress.com T-SQL Coding Standards And Best Practices for developers
Rationale Witness to totally messed up databases Perspectives of a lot of developers regarding SQL Server (or any database system): Hostility towards SQL Server (the database system) High priority to the client application Back-end nature of SQL Server (the database system) Any more reasons why you do not like SQL Server?
Why naming conventions? Reduces the effort needed to read and understand Increases the fluency in identifying objects Do you use naming conventions?
Object Naming Conventions Tables: Use upper camel case Do not use underscores to separate words Use the plural form of nouns E.g.: EmailAddresses, Customers, SalesInvoices For relationship tables combine the related tables names E.g.: StudentsCourses Consider using Schemas (in SQL Server 2005 and later) to group related objects (in databases with large structures) Suggestions?
Object Naming Conventions Field Names: Use upper camel case Do not use underscores to separate words Use the singular form of nouns E.g.: FirstName, DateOfBirth Using the data type as a prefix is not considered a best practice anymore For identity column names use table name suffixed with ID Suggestions?
Other SQL Server objects Views: vwSalesSummary2007 Indexes: IX_Customers_SocialSecurityNumber Stored Procedures: Do not prefix with sp_ Names based on functionality: Get: GetSalesInvoices Insert: InsertCustomers Update: UpdateCourses References: http://vyaskn.tripod.com/object_naming.htm http://www.cms.hhs.gov/dbadmin/downloads/sqlserverstandardsandguildelines. pdf http://www.cms.hhs.gov/dbadmin/downloads/sqlserverstandardsandguildelines. pdf Object Naming Conventions
Prettifying the Horrifying Why prettify? Readability by others Readability by self Results in: Ease of debugging and modifying of code
Prettifying the Horrifying How to prettify? Indents Comments Upper case for keywords Shortening lines Use square braces for table/view names and column names Use table aliases using Use tabs instead white spaces Suggestions?
Standards for creating tables Make sure all tables are in the 3 rd Normal form Primary keys for unique row identification Choosing a primary key Natural key vs. Surrogate key Natural keys have a tendency to change An integer identity (surrogate) column is the best suited [UserID] int IDENTITY(1,1) Avoid GUID/UNIQUEIDENTIFIER data types for primary key Reference: http://databases.aspfaq.com/database/what-should-i-choose-for-my-primary- key.html http://databases.aspfaq.com/database/what-should-i-choose-for-my-primary- key.html
Standards for creating tables Choose data types with the minimal size as possible Use Unicode data types only if it is needed Make sure data integrity is applied Primary keys, Foreign keys, Check, Default and Unique constraints Keep in mind the 8060 B row size rule Choose varchar(max), nvarchar(max) and varbinary(max) over text, ntext and image
Standards for creating tables Avoid storing BLOBs in tables especially if there is constant access Alternatively: Store the path in the table and the data in files Store the data in a varbinary(max) field using FILESTREAM (SQL Server 2008)
Querying Tips Rather than SELECT * FROM … use SELECT [col1],… [coln] FROM … Select only the columns that are required for output Use Common Tables Expressions (CTEs) wherever possible instead of temporary and derived tables SET NOCOUNT ON within batches and stored procedures to increase on performance
Querying Tips Avoid cursors as much as possible Alternatively use: Set based approach to update or insert data from one tables to another Tables variable and While loop (suited for small result sets) Wild card characters at the beginning of a phrase in the LIKE clause should be avoided WHERE [Name] LIKE %Powell Refer to table names with schema name prefixed … FROM [HumanResources].[Employee ]
Querying Tips Prefix column names with table name or alias SELECT Employee.[Name], Contact.[Address] FROM … Avoid using functions on columns in the WHERE clause WHERE UPPER([Name]) = BARBIE Declare all variables and initialize values at the beginning of the code (Makes the query optimizer reuse plans) When checking for existence of records, simply use IF EXISTS(SELECT * FROM dbo.Employees). It does not return a result set, hence is fast.
Querying Tips Avoid dynamic SQL Try to find alternatives that do not constitute of dynamic SQL. If at all using dynamic SQL, use sp_executesql instead of EXECUTE ( EXEC ) When testing query performance using the graphical execution plan, look for Index seeks over Index scans or Table scans. When performing Inserts, use column list in the INSERT clause: INSERT INTO ([Name], [Age], [Address]) VALUES (Neil, 32, Hendala Junc.)
Querying Tips Place all data access tasks in SQL Server itself. Avoid queries and data manipulations on the client app/business tier. Use stored procedures Reference: http://blog.sqlauthority.com/2008/09/25/sql-server- guidelines-and-coding-standards/ http://blog.sqlauthority.com/2008/09/25/sql-server- guidelines-and-coding-standards/ Suggestions?
Perform all referential and domain integrity rules using constraints Avoid using triggers for this purpose (poor performance) Use only if cannot be implemented by constraints Avoid triggers for business functionality Less visible Can avoid indirect recursion problems Alternatively use stored procedures Triggers can be used for tasks such as auditing and custom validations
Trigger Mania When writing triggers Write for a recordset rather than for a single record Suggestions?
Q1 You have an SQL Server 2008 database. You need to load data from one table to another. New records will have to be added, existing records need to be updated and records not in the source should be deleted from the destination. How would you perform this with best performance? Using the MERGE statement
Q2 You use an SQL Server 2005 database. You need to store map images which are between 50MB and 100MB in size. What is the optimum method to perform the storage? Store the images in the file system and the file path in an SQL Server table
Q3 What alternatives can be used for cursors? Set based operations Table variables and WHILE loop (for small data sets)
Q4 Name some Best Practices for triggers. Avoid using business functionality within triggers Code for record sets rather than single records Best suited for auditing and other custom tasks
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