sql server varchar max performance

are: not,! =, 10. Use Delete sparinglyIn general, some of the logic of deleting data will be implemented more or less in stored procedures. For a small number of tables, the problem is not very big. But for large data tables, deleting data with delete can have a certain effect on the performance of the stored procedure. Because delete takes a full table-by-scan approach, it is a transactional operation that is counted into the

It's been a long time since you've written, and DBAs typically have to test server performance before the system is officially online. For example, you have a lot of servers, some do Web server, some do cache server, some do file server, some do database

In earlier articles, the detect methodology in performance tuning was mentioned, and the Detect methodology was briefly reviewed here.Discover the problem: finding problemsExplore The conditions: Reasons to exploreTrack down possible approaches: providing a possible solutionExecute the most likely approach: perform the best possible solutionCheck of Success: Confirm success (if not successful, repeat the above steps)Tie up Loose Ends: complete Remaini

to the table will cause the view to not be automatically added, although we can refresh the view by Sp_refreshview or sp_refreshmodule, but to avoid confusion, It is best to explicitly list the name of the required column in the view definition, and if additional columns are added and we need additional columns in the view, we can modify the view definition by Alter VIEW.View query returns extra columns resulting in inefficient query performance thro

example, the following example uses the pubs database. SELECT au_id, au_lname, au_fname from authors WHERE au_lname = ' White ' The indexes established on the following columns will be useful indexes for the optimizer ? au_lname ? au_lname, au_fname The indexes that are built on the following columns will not work well for the optimizer ? au_address ? au_fname, au_lname Consider using narrow indexes on one or two columns, narrow indexes are more efficient than multiple indexes and composite ind

Tags: ber write amp order parameter IO performance HDD persistence anotherThis article focuses on common metrics for using Performance Monitor to monitor SQL Server under Windows, including the buffer Cache hit Ratio, pages/sec, Available Bytes, Disk Time, AVG. Disk Queue Length, Processor time, Processor queue Length,

A Introduced Some "super users" with access to data have learned professional Transact-SQL. The convenience of the Report Builder in SQL Server 2005 Report Services (SSRS) extends to the creation of powerful Transact-SQL queries, making it easier for more users to use it. Their ability to consume system resources is b

Because SQL Server 2000 lacks some high-end performance, it is considered a 90-pound little. In fact, no strong person can accomplish every feat, and no company needs every high-end feature. For years, many large and small businesses have been using SQL Server to run their c

The database SQLServer is born with the same parent in the Windows operating system, and they have technical connectivity. This is reflected in many aspects. For example, in our daily work, we can adjust some parameters of the Windows operating system to improve the performance of the SQL Server database server. I. res

: here, both have been positioned to occupy One of the CPUs high in SQL , which can combine the efficiency of business scenarios and SQL , and whether communication with developers such as/DBA is optimized or how to optimize (By the way, it is suggested that the amount of data in the database will have a large impact on the performance gap, this test, 10W of

will query through the indexed range query LODGING_PKBecause the index range query will return a set of values, its efficiency will be the peso cited as the only scan lowerExample 2SELECTfromUserWHERE='mrzhang ';This SQL is executed in two steps, Lodging$manager the index range query (get all rowid that match the condition record), and get the value of the lodging column through the ROWID Access table.Because Lodging$manager is a non-unique index, th

When installing SQL Server 2003 Development edition and Enterprise Edition on Windows Server 2000, Windows XP, or Windows 2008, the "performance counter registry Configuration unit consistency" check will fail (Windows Server 2008 has not been tested due to no environment cu

When executing SQL queries, the main bottlenecks are: CPU computing speed, large memory cache area When executing SQL queries, the main bottlenecks are: CPU computing speed, large memory cache area When executing SQL queries, the main bottlenecks are: CPU computing speed, memory cache size, and disk IO speed. For queries of large data volumes, the bottleneck i

, which avoids longer locking of the system tables.25. Avoid using cursors as much as possible, because cursors are inefficient and should be considered for overwriting if the cursor is manipulating more than 10,000 rows of data.26. Before using a cursor-based method or temporal table method, you should first look for a set-based solution to solve the problem, and the set-based approach is generally more efficient.27. As with temporary tables, cursors are not unusable. Using Fast_forward cursors

smallertable (Lookupcolumn) Look at the query execution plan for both At this point we see the above query execution plan, we can clearly see the left JOIN .... Is null or full JOIN then after filtering, just after creating the index performance improved a little, but unlike the left JOIN ... Is null for not exists the planned execution is different from not creating an index, at this point the flow aggregation is used first and then the right half

What is database partition?Database partitioning is a type of horizontal table segmentation. This technology is provided by SQL Server 2005 Enterprise Edition and later SQL Server versions. This type of horizontal table segmentation is different from that in SQL

I. Preface Index plays an important role in database performance. The advantages and disadvantages of index design directly affect the efficiency of DB execution. Therefore, when performing DB tuning, some of them will start to process the index. SQL server also provides a good tool for Database Engine Tuning Advisor and provides some advice on index creation and

level is very limited, there is said wrong or understanding not in place also hope that the great God to correct, lest mislead others, greatly appreciated.Follow-up will continue to write some practical experience in SQL Server query performance optimization, mainly include the following aspectsSQL Server query

server| Problem | performance 1. To optimize the query, you should try to avoid full table scan, first consider the where and the order by the columns involved in the establishment of the index. 2. The null value of the field in the WHERE clause should be avoided as far as possible, or it will cause the engine to discard the use of the index for a full table scan, such as:Select ID from t where num is nullY

deduplication operations we mentioned in the previous article.How can we see a merge interval deduplication? In fact, the reason is very simple, because we have sorted the results before using this operator, and the duplicate values of the sorted results items are closely tied together, therefore, the merge interval method is introduced for processing, so the performance is the best.More importantly, the application scenario of the merge interval ope