udacity statistics

-- ------------------------ SELECTDate, MAX(CASENAMEWHEN‘小说‘THENScount ELSE0 END) 小说, MAX(CASENAMEWHEN‘‘ THENScount ELSE0 END) FROMTabName GROUPBYDate 　　 --- ----------------------- --row-to-column statistics ----------- --------------- select NBSP;NBSP;NBSP;NBSP; date name ,scount) As b_str from NBSP; group by date /table>

The LAG () and lead () statistics functions are able to fetch the first n rows of the same field and the values of the last n rows in a single query . Such operations can be implemented using table joins to the same table, but using lags and leads is more efficient. The following examples of lag () and lead () are organized:LAG (expression,Sql> Select Year,region,profit, Lag (profit,1) over (order by year) as 51xit_exp from test;Year Region PROFIT 51x

Original: 12th Chapter--sqlserver Statistics (4)--statistical information on the filtered indexObjective:From The beginning, a new feature is introduced to enhance the nonclustered index-filter index, youcan use a statement with a where condition to create a nonclustered index, filter out the unwanted data, Improve query performance by reducing maintenance overhead and storage space for indexes.Preparatory work:On the AdventureWorks2012 , there is a

) {collection.update ({"Name": Name, "Time.day":d ay, "title": title},{$inc: {"PV": 1}},function (ERR) {mongodb.close (); if (err) return callback (ERR);}); Doc.post=markdown.tohtml (doc.post);d Oc.comments.forEach (function (comment) {comment.content = markdown.tohtml ( comment.content);});} Callback (null, DOC);//return query for an article});});};Note here: Collection.findone ({"Name": Name,"Time.day": Day,"title": Title}, function (Err, doc) {if (err) {Mongodb.close ();Return callback (ERR);

likelihood function called a sample. Any observations of the sample (), if is called the maximum likelihood estimate of the parameter, which is the maximum likelihood estimator of the parameter. If or about differentiable, the maximum likelihood estimate of the parameter can be obtained by the equation: Get. For the monotone function, the maximum likelihood estimate of the parameter can also be obtained by the equation: , the solution of the latter one is often much more convenient than the

There are two tables: MessageInfo and MessageType. The table structure is as follows: Then we need to implement the following query results: This is what I encountered during the interview, and the above news type is gibberish. I didn't do it at the time, and then I came back and studied it again. At the beginning, the news type table MessageType left connected to leftjoin new There are two tables: MessageInfo and MessageType. The table structure is as follows: Then we need to implement the fol

Collect Oracle statistics Optimizer statistical range: Table statistics; -- number of rows, number of blocks, average length of rows; all_tables: num_rows, blocks, avg_row_len;Column statistics; -- the number of unique values in the column, the number of null values, and the data distribution;-- Dba_tab_columns: num_distinct, num_nulls, histogram;Index

Introduction to statistics management of Optimizer1. Preface In our daily maintenance, we accept some systems that have been running well for a long time. suddenly one day, the user did not perform any operation. It took only a few seconds for a function module of the system or a report, but now it takes several minutes or longer to return the result. In this case, we usually analyze the SQL statement and find that the SQL Execution Plan has changed.

Collect statistics from ORACLE Link: http://blog.itpub.net/2317695/viewspace-1226138/Today, I saw an article on Statistics Collection on the Internet, which is not bad. 1. Understand what is statistical information Optimizer statistics are a set of objects that describe databases and databases in more detail. These statistics