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SQL random Query
SQL Server:
Select Top N * from Table order by newid ()
The newid () function creates a unique value of the uniqueidentifier type. The preceding statement reads N records randomly from the table.
MySQL: Select * from Table order by rand () limit 10
STR converts a number to a string for compa
output stuid=3)Stuid=4 .....Therefore, the Select Assignment statement in the dynamic row to column above can be interpreted as:The results from the back of the (select course from scores) are assigned to the course variable one at a time, and the operation after each copy is: string connectionSoSelect @sql [email protected] + ' max (case course if ' +course + ' then score else 0 End '+ ' + ' + ' + ', ' fr
Ind_attribute.is_ Disabled as [is disabled] 4 from (5 select Tab_name,index_name, [Co_names]=stuff ((SELECT ', ' +[co_name ') from 6 (select Tab. Name as Tab_name,ind. Name as index_name,col.name as Co_name from sys.indexes IND 7 INNER JOIN Sys.tables tab on Ind. object_id = tab.object_id and Ind.type in (8) inner join sys.index_columns index_columns on tab.object_id = Index_colu mns.object_id and ind.index_id = index_columns.index_id 9 inner join sys.columns Col on tab.object_id = col.object_i
It is understood that the vast majority of developers have a thorough understanding of indexing, limited to the fact that most daily work has no chance, and there is no need to care about or understand indexing, when a query is too slow, you can create an index based on the query conditions. When another query is slow, you can create an index, or directly send th
it is to increase I/O.2. Vertical and horizontal partition table, reduce the size of the table (Sp_spaceuse)3. Upgrading hardware4, according to the query criteria, index, optimize the index, optimize access mode, limit the data volume of the result set. Note that the fill factor is appropriate (preferably using the default value of 0). The index should be as small as possible, using a Lie Jian index with a small number of bytes (refer to the creatio
The word booksearch may be unfamiliar to many developers. Many people have encountered this word, but they have not paid enough attention to it, so they have always ignored its existence.
The word booksearch may be unfamiliar to many developers. Many people have encountered this word, but they have not paid enough attention to it, so they have always ignored its existence.
The growth of SQL Server Cognit
(TRUE ), when the write lock is performed, all Query Cache related to the table will be invalidated. If it is set to 0 (FALSE), the Query Cache related to the table can still be read at the lock time.
3. Query Cache and Performance
Nothing is too late, especially for systems with frequent writes, enabling the Query Ca
The growth of SQL Server Cognition
1. I don't have to graduate or work for a long time. I only know the relationship between SQL and SQL Server Oracle and MySql. I usually think that SQL is S
Small Program Ape SQL Server Cognitive growth
1. Did not graduate or work not long, only know that there is a database, SQL such dongdong, unaware of the SQL and SQL Server Oracle, MySQL relationship, usually considered
Label:1. View the user tableSelect from Sys.tables Select from where type='U' Select from where xtype='U' where type or xtype value:U = user table S = system table V = view FN = scalar function TF = table function P = stored procedure
TR = Trigger
D = defaults or Default constraints PK = PRIMARY KEY constraintF = FOREIGN KEY constraint UQ = UNIQUE constraint SELECT from Information_schema. TABLES2. View ViewSELECT * from Information_schema. Views3. View the table/view fieldsS
Label:There are three basic types of joins: Cross joins, Inner joins, and outer joins. The cross join has only one step-cartesian product; There are two steps in the inner join-Cartesian product, filtering, outer join has three steps-cartesian product, filtering, adding outer row.Inner joinsCode: SELECT e.empid, E.firstname, E.lastname, O.orderid
from as E
JOIN as O
on = O.empid; Another way to do this: SELECT e.empid, E.firstname, E.lastname, O.orderid
from as as O
WHERE = O.e
It is understood that most developers have a smattering of understanding of the index, limited to most of the daily work no opportunity, what is not necessary to care about, understand the index, it is really a query too slow to find the query conditions to build an index on OK, which day again a query slow, and then establish an index is, Or simply send the enti
There are many reasons for slow query speed in SQL Server databases. The following are common causes:
1. No index or no index is used (this is the most common problem of slow query and is a defect in programming)
2. Low I/O throughput, resulting in a bottleneck effect.
3. the query
The growth of SQL Server Cognition 1. I don't have to graduate or work for a long time. I only know the relationship between SQL and SQL Server Oracle and MySql. I usually think that SQL is SQ
Myth 1. An index is established on a table and an indexed column is used at query time, and the index is bound to take effectFirst of all, it is wrong to make it clear that the SQL Server query optimizer is a cost-based optimizer that determines whether to use an index, what type of index to use, and which index to use
Tag: Style color IO using strong SP data on problemIn recent times, has been exploring the SQL Server query performance issues, of course, also aimless search for a lot of information, but also from the online great God's articles learned a lot, here, to the great God salute. It is by the great God selfless dedication of the influence of the spirit, so, the young
This article introduces parameterized query. I will discuss how SQL Server optimizer attempts to parameterize a query and how you can create your own parameterized query if the query can be parameterized.
This article introduces p
What is parameterized query?
A simple way to understand parameterized queries is to think of it as just a T-SQL query that accepts parameters that control what the query returns. By using different parameters, a parameterized query returns different results. To obtain a para
SQL Server stored procedure dynamic parameter call implementation code. For more information, see.
SQL Server stored procedure dynamic parameter call implementation code. For more information, see.
Just take notes. nothing !!
The
Label:Original: 1th week how SQL Server executes a queryHello everyone, Welcome to the 1th week of SQL Server Performance Tuning training . Before we go into the tedious details of SQL Server performance tuning, I want to build th
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