indexing

问题 I'm interested to find out if there is a performance benefit to partitioning a numeric column that is often the target of a query. Currently I have a materialized view that contains ~50 million records. When using a regular b-tree index and searching by this numeric column I get a cost of 7 and query results in about 0.8 seconds (with non-primed cache). After adding a global hash partition (with 64 partitions) for that column I get a cost of 6 and query results in about 0.2 seconds (again

问题 I have calculated a series of totals tips by day of a week and appended it to the bottom of totalspt dataframe. I have set the index.name for the totalspt dataframe to None. However while the dataframe is displaying the default 0,1,2,3 index it doesn't display the default empty cell in the top left directly above the index. How could I make this cell empty in the dataframe? total_bill tip sex smoker day time size tip_pct 0 16.54 1.01 F N Sun D 2 0.061884 1 12.54 1.40 F N Mon D 2 0.111643 2 10

问题 Been searching for a solution for a while now, go to (1) or (2) to skip description, first i will explain the situation. My firm have upgraded our erp. system, my primary work is to create lists used by others in the firm, i take all my data from this systems database during upgrade we got some data converted to match the new version, some of it was left behind, some of it was not tampered with and just directly exported to the new database, its on a separate server, basically its a success,

问题 I'm trying to index large 3D arrays using a 2D array of indicies from argmin (or related argmax, etc. functions). Here is my example data: import numpy as np shape3d = (16, 500, 335) shapelen = reduce(lambda x, y: x*y, shape3d) # 3D array of [random] source integers intcube = np.random.uniform(2, 50, shapelen).astype('i').reshape(shape3d) # 2D array of indices of minimum value along first axis minax0 = intcube.argmin(axis=0) # Another 3D array where I'd like to use the indices from minax0

问题 Some searching through Google (and my own experience) shows that in PHP you can't grab an array element when it's been returned from a function call on the same line. For example, you can't do: echo getArray()[0]; However, I've come across a neat little trick: echo ${!${false}=getArray()}[0]; It actually works. Problem is, I don't know why it works. If someone could explain, that would be great. Thanks. 回答1: echo ${!${false}=getArray()}[0]; This is how it works, step by step ${false}=getArray

问题 this is my struct : struct Node { struct Node* data; struct Node* links[4]; } assuming there is no padding, does Node->links[-1] guaranteed to be pointing on Node::data ? 回答1: No guarantee; this is undefined behaviour: Compiler-dependent structure padding Standard only defines array indexing between 0 and length (inclusive) Possible strict-aliasing violation In practice, it's quite possible that you will end up pointing at data , but any attempts to access it will result in UB. 回答2: Array

问题 In the many search functions of C (bsearch comes to mind) if a result is found, a pointer to the spot in the array is returned. How can I convert this pointer to the index in the array that was searched (using pointer arithmetic, i assume). 回答1: ptrdiff_t index = pointer_found - array_name; 来源： https://stackoverflow.com/questions/2711653/c-how-to-convert-a-pointer-in-an-array-to-an-index

问题 What does this mean and how can I fix it? 回答1: You have two separate indexes on the same field of your table ( id ). One of them is implied by having set id as a PRIMARY KEY , the other you probably created explicitly. Only one of them is needed - having both of them may result in performance drop due to the additional index updates. Just drop one of them to resolve this issue. Having a PRIMARY KEY or UNIQUE constraint on a column (or field, if you wish) of a table essentially means that for

问题 We have large MS SQL database with many tables and foreign keys. We need to index all foreign keys in our tables due to performances and we are trying to avoid do it manually. Is there any way to MS SQL do it automatically or with some tools? MS SQL server used is MS SQL Server 2008 R2. Thanks a lot. 回答1: I'd steer you away from trying to do this automatically and encourage you to examine your system (Google missing index DMVs (SQL 2005 or later) for a good start) and create appropriate

问题 I'm building a small web search engine for searching about 1 million web pages and I want to know What is the best way to build the inverted index ? using the DBMS or What …? from many different views like storage cost, performance, speed of indexing and query? and I don't want to use any open source project for that I want to make my own one! 回答1: Perhaps you might want to elaborate why you do not wish to use F/OSS tools like Lucene or Sphinx. 回答2: Most of the current closed-source database