deduplication rate

In the table, duplicate values may be included. That's not a problem, but sometimes you might want to just list different values (distinct). Keyword DISTINCT is used to return only different values.Table A:Example 1Select distinct name from AThe following results are performed:Example 2Select DISTINCT name, ID from AThe following results are performed:is actually based on "Name+id".Example 3: StatisticsSelect COUNT (distinct name) from A; --The number of the table name to go back to, SQL Server

Php array deduplication and analysis. Duplicate items in one-dimensional array: Use the array_unique function. use the following example: Copy the code as follows :? Php $ aaarray (apple, banana, pear, apple, wail, watermalon); $ Repeated items in one-dimensional array: Use the array_unique function. use the following example: The code is as follows: $ Aa = array ("apple", "banana", "pear", "apple", "wail", "watermalon ");$ Bb = array_unique ($ a

directory. Result indicates the entire record. File obtains the final output file name, hash, bitwise operation, and modulo operation for output balancing. Map output structure The purpose of this operation is to ensure that the same record has the same key and save the type. Partition needs to press left of textpair, that is, this key, This ensures that all records to be written to the same output file are written to the same reduce. One reduce can write multiple output files, but one output f

Note: It tells you that N numbers allow you to keep one repeated number and sort the output. Analysis: Store a number every time it is read. There were countless RESS yesterday because I first output the first one and then output each one in sequence. The problem is that if only one element needs to access the first element Code: 1 #include View code 1 #include Array Simulation Hlg1287 number deduplication and sorting II [hash]

(*) from gczbxx_zhao t group by gcmc, gkrq having Count (*)> = 1 order by GKRQ) Select * from gczbxx_zhao where viewid in (select max (viewid) from gczbxx_zhao group Gcmc) order by gkrq desc --- this is feasible. .One question says: the efficiency of distinct deduplication is very low. I saw this article on the Internet as if it was very efficient to use group by having?In a test, I have a product table with 0.26 million records. Only the product num

ZOJ question 2734 Exchange Cards (DFS deduplication OR primary function) Exchange Cards Time Limit: 2 Seconds Memory Limit: 65536 KB As a basketball fan, Mike is also fond of collecting basketball player cards. but as a student, he can not always get the money to buy new cards, so sometimes he will exchange with his friends for cards he likes. of course, different cards have different value, and Mike must use cards he owns to get the new one

004 string deduplication (keep it up), 004 keep Design algorithms and write code to remove repeated characters in strings. No extra cache space is available. Note: one or two additional variables can be used, but an additional array copy is not allowed. Simple question: #include Keep it up writes several algorithm questions every week, entertainment! What is keep it up? Keep upPersistence; maintenance; continue; Do not low; do not bend (disease, et

// Array Function Extension array. prototype. each = function (FN) {fn = FN | function. k; var A = []; var ARGs = array. prototype. slice. call (arguments, 1); For (VAR I = 0; I This article from the "Dream think Xi" blog, please be sure to keep this source http://qiangmzsx.blog.51cto.com/2052549/1549392 Array Function Extension-difference set, Union set, collection, deduplication

functionremoverepetition (str) {varresult = "", Unstr; for(vari=0,len=str.length;i){ //because UNSTR is always the previous letter of the current Str.charat (i) because the assignment of Unstr Unstr=str.charat (i) is done in the previous cycle //so you can delete the place where it repeats. if(Str.charat (i)!==unstr) {Unstr=Str.charat (i); Result+=Unstr; Console.log (result); } } returnresu

Let's say we have a MongoDB collection, Take this simple set as an example, we need to include how many different mobile phone numbers in the collection, the first thought is to use the DISTINCT keyword, Db.tokencaller.distinct (' Caller '). length If you want to see specific and different phone numbers, then you can omit the length property, since Db.tokencaller.distinct (' Caller ') returns an array of all the mobile phone numbers. However, this approach is sufficient for all situations.

name,address, which requires the result set to be unique for both fieldsSelect Identity (int,1,1) as Autoid, * into #Tmp from TableNameSelect min (autoid) as autoid into #Tmp2 from #Tmp Group by name,autoidSELECT * from #Tmp where autoid on (select Autoid from #tmp2) The last select is the result set that name,address not duplicate (but one more autoid field that can be written when actually writing Omit this column in the SELECT clause) (iv) Duplication of queriesSELECT * FROM tablename where

groupedSuch as:-The total number of girls and boys receivedSelect Sex,count (*) from Student GROUP by sexOrder of Query statements:Select from where the group by has an order byNote: Where is the filter for the source data. It can only use columns that are referred to in the table following the fromAn aggregate function cannot be used after a where condition, and an error will be made if usedHavingIf you are filtering the result set after grouping, then you need to have a having, because the wh

1, use distinct to weight (suitable for querying the total number of the whole table)There are multiple schools + teachers to contribute, need to count the total number of authorsSelectcount (author)As total from files each author has a lot of contributions, there are duplicate records here. Selectdistinctauthor from files;It is possible that the names of teachers in both schools are the same, and only one error is counted. SelectdistinctAuthor,sid the combined unique value of the From files sta

Tag: equals code uses element delete to perform dev repeat hashTo insert into the database go to weight: 1. Iterate through the list you have read 2. Get the data you need to query before you insert the method into the database, execute the Query method 1 devlist=devicedao.finddevice (Device.getrfid ()); 2 if (Devlist.size () >0) { 3 messagestr = "Duplicate data, please re-import!" "; 4 5 } Else { 6 devicedao.save (device);

)Create Tabletmp_relationship_id as(Select min(ID) asId fromRelationshipGroup bySource,target having Count(*)>1)Create an indexAlter Table Add index name (field name)DeleteDelete from Relationship where not inch (Select from tmp_relationship_id) and inch (Select from relationship)2.2 Quick MethodIn practice, it is found that the above method of removing field duplication, because there is no way to rebuild the index for multiple fields, resulting in large data volume is very inefficient, lo

of the above mechanism, using the drop of a table or delete data, the space will not be self-Recycle, for some of the tables that are determined not to be used, when removing the space at the same time, there are 2 ways to do this:1, the use of Truncate method for truncation. (But data recovery is not possible)2. Add purge option at drop: drop table name purgeThis option also has the following uses:You can also delete the table permanently by deleting the recyclebin zone, and the original delet

Today, my friend asked a particularly tangled question: in a database table, we need to repeat a field in the table and sort the remaining data by another field, Today, my friend asked a particularly tangled question: in a database table, we need to repeat a field in the table and sort the remaining data by another field, Today, my friend asked a particularly tangled question: In a table in the database, the table duplicates a field in the table and sorts the remaining data according to ano

t group by gcmc, gkrq havingCount (*)> = 1 order by GKRQ)Select * from gczbxx_zhao where viewid in (select max (viewid) from gczbxx_zhao groupGcmc) order by gkrq desc --- this is feasible..One question says: the efficiency of distinct deduplication is very low. I saw this article on the Internet as if it was very efficient to use group by having?In a test, I have a product table with 0.26 million records. Only the product number is indexed and the br

The group by statement can deduplicate a column.Directly run the preceding statement: select io_dev_id from io_info where (TID = 1 AND host_name = 'yang1') group by 1; deduplication BY io_dev_id. P: The difference between order by and distinct is that group by is used to select order by Based on the column. distinct is similar to group by, but it can only be placed behind select, the front of the filtered field. For example, select distinct a, B, c fr

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