how to write distinct query in sql

Label:Today, I ran into a problem with a Sybase database query. A simple SQL, but do not know why the query does not come out, resulting in the production of the production server frequently hang out. Scared my little heart to bang. Select as Fcilcde from dnd_event_log A WHERE a.doc_ref =? and A.doc_type =? ' S ' Later, the network Operations Manager, the

Method 1:When the publisher filter condition is NULL, how do you write SQL?1 DECLARE @publishers VARCHAR (50);2 SELECT * FROM dbo. Book WHERE Publishers=isnull (@publishers, publishers)Method 2:DECLARE @cinv varchar (50)SELECT * from inventory where 1=1 and ([email protected] or @cinv is null)Method 3:DECLARE @name VARCHAR (+), @page INT =1SET @name = ' Zhang San 'DECLARE @

------------------------------------------------------------------------------------------------------------------------Displays the disk activity volume generated by the transact-SQL statement.Set statistics Io on-- Disable the disk activity volume generated by the transact-SQL statement.Set statistics Io off-- Display [return detailed information about statement execution and estimate the resource require

From: http://www.cnblogs.com/huacn/archive/2007/04/28/ SQL _Prompt_3.html A good SQL query analyzer auxiliary tool found yesterday. SQL prompt 3 is not cracked, and it seems to be a 15-day trial.Its main function is to automatically detect the SQL

directing SQL Server to execute with other query schemes. This method requires: 1. The function to be done on the statement is clear, 2. The structure of the data table to be queried is clear, 3. The relevant business background knowledge is clear. If this method can be solved, of course, it is also a good solution. However, sometimes SQL Server is smarter, and

. This method requires: 1. The function to be done on the statement is clear, 2. The structure of the data table to be queried is clear, 3. The relevant business background knowledge is clear. If this method can be solved, of course, it is also a good solution. However, sometimes SQL Server is smarter, and even if you tweak the statement structure, it does not affect its execution plan.How to compare the performance of two

different. SELECT * FROM dual Select * from dual In fact, the case is different, the Query Analyzer is considered to be two different SQL statements, must be parsed two times. Generate 2 execution plans. So as a programmer, you should ensure that the same query statements everywhere are consistent, one more space is not! 3. Do not

m.meetingname= ' ¨??????????? ¨¨ ' and M2. Meetingname= ' ¨??????? ¨°??? ¤?é?1 ' and m.employeename=m2. EmployeeName(Please refer to the above for garbled questions)Multi-table ConnectionMultiple table joins can actually be seen as n-1 two-table connections to n tables. This understanding makes the problem much easier!For example, the top three tables, the first two tables we have already begun to understand in the article, suppose now added a teacher table, the three tables to the Carte

1 Overview During the recent maintenance of the system, the customer often reports that a query condition should be added to the query list. This requirement is not too much at all, and it seems that the workload is not great, it is not to add a where condition, but when debugging to the Dal layer, petrochemical now -- an SQL statement used to

SQL _ write a simple Stored Procedure for deleting employee information, SQL stored procedure Original Works are from the blog of "Deep Blue blog". You are welcome to reprint them. Please note the following source when reprinting them. Otherwise, you will be held legally liable for copyright. Deep Blue blog:Http://blog.csdn.net/huangyanlong/article/details/439389

the same, then the greater than and equals sign are the same)1.select gid,fariqi,neibuyonghu,reader,title from Tgongwen where fariqi> ' 2004-1-1 ' and fariqiSpents: 3280 milliseconds4. The date column will not slow down the query speed because there is a minute or seconds inputIn the following example, there are 1 million data, 500,000 data after January 1, 2004, but only two different dates, the date is accurate to the day, before the data 500,000,

the database query optimizer thinks it is different. SELECT * FROM dual Select * from dual In fact, the case is different, the Query Analyzer is considered to be two different SQL statements, must be parsed two times. Generate 2 execution plans. So as a programmer, you should ensure that the same query statements ev

IntroductionA few days ago to do such a thing: a game has an activity page, the Activity page has a product, the product below to show the actual number of views, it is equivalent to the user every request for the total number of visits will be added once, the problem is simple, each time you browse to the database to do "+1" operation. But when I do, I can dilute the SQL request and reduce the number of "+1" requests due to the fact that the total nu

not exist in buffer pool, buffer Manager asynchronously initiates an IO operation that reads the requested page from the storage system into buffer pool, which is called a physical read (physical read).　　The entire query must wait for the physical read of the asynchronous operation to complete before we week22, and then discuss some of the details of the wait. Once all the request pages are read into buffer Pool, they are returned to access Methods,

Original: SQL query performance analysisOriginal source: http://blog.csdn.net/dba_huangzj/article/details/7623926The performance of SQL query directly affects the value of the whole database, which must be treated solemnly.SQL Server provides a variety of tools, and here's a simple introduction:First, the

between commit and Rollback Rollback: Roll back all things. Commit: Commit the current thing. There is no need to write things in dynamic SQL, if you want to write please write outside such as: Begin TRAN EXEC (@s) commit trans or write dynamic

demonstrate how to use the ASP. NET project to query data.The northwind database modeled by using LINQ to SQL In the second article of this series, I explained step by step how to use the lint to SQL designer built in vs2008 to create a LINQ to SQL class model. The following is the class model we created for the north

Top keyword: write in front of the field after selectFor example, you want to display the first 5 records of a query, as follows:Select Top 5 * from StudentIn general, top is the same as the order byOrder by uses the order by after the name of the table to fill in the fields you want to sort by, in ascending order (from small to large)Percent: Percent%=percentFor example, to display 5% of data processing, c

N SQL> select empno, ename, job, Mgr, hiredate, Sal, comm, deptno from EMP where ename like '% N % '; Case: Query employee information with the second to last character % in employee name SQL> select empno, ename, job, Mgr, hiredate, Sal, comm, deptno from EMP where ename like '% \ % _ 'escape '\'; Case: query the tot

original index was divided into clustered index and non-clustered index, and burst into tears. I finally knew what the index was. 4. Further study: clustered indexes are physical indexes, non-clustered indexes are logical indexes, and clustered indexes are the storage sequence of data. Non-clustered indexes are logical indexes that are used for clustered indexes. 5. then I learned how to view the execution plan. I finally got a rough idea about the query