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Group by with multiple columns using lambda
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@Jacob - Anonymous types are immutable classes with properly overriden GetHashCode & Equals methods. They where designed for exactly this kind of use case.
– Enigmativity
Aug 4 '11 at 2:57
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【解决】Linux mysql如何重置root密码？ - 更多技术 - 清泛网 - 专注C/C++及内核技术
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4. 略过grant授权表启动mysql/MariaDB服务
启用--skip-grant-tables选项后，任何人都可以在没有密码和所有权限的情况下连接到数据库服务器：
mysqld_safe --skip-grant-tables &
上面命令末尾的＆符号将导致程序在后台运行，因此我...
App Inventor 2 TableView 拓展：TableView 拓展：数据表格视图，表格展示...
...索 App Inventor 2 TableView 拓展：TableView 拓展：数据表格视图，表格展示数据
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Storing JSON in database vs. having a new column for each key
I am implementing the following model for storing user related data in my table - I have 2 columns - uid (primary key) and a meta column which stores other data about the user in JSON format.
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Why do people hate SQL cursors so much? [closed]
...I. Cursors are how parts of the RDBMS work under the hood. Often CREATE TABLE and INSERT have SELECT statements, and the implementation is the obvious internal cursor implementation.
Using higher-level "set-based operators" bundles the cursor results into a single result set, meaning less API b...
Why can't C# interfaces contain fields?
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The virtual keyword is implemented in .NET with methods and a so-called v-table, an array of method pointers. The override keyword fills the v-table slot with a different method pointer, overwriting the one produced by the base class. Properties, events and indexers are implemented as methods und...
How do I make a list of data frames?
... data import function for read.csv as appropriate. readr::read_csv or data.table::fread will be faster, or you may also need a different function for a different file type.
Either way, it's handy to name the list elements to match the files
names(my_data) <- gsub("\\.csv$", "", my_files)
# or, ...
Is there any difference between GROUP BY and DISTINCT
...river :: GroupBy : Distinct and screw => get list of unique values in a table column)
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When is CRC more appropriate to use than MD5/SHA1?
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I found a study that shows how inappropriate CRC hashes are for hash tables. It also explains the actual characteristics of the algorithm. The study also includes evaluation of other hash algorithms and is a good reference to keep.
The relevant conclusion on CRC for hashes:
CRC32 was neve...
SqlException from Entity Framework - New transaction is not allowed because there are other threads
...for performance for large datasets? If you have a millions records in the table. ToList() will suck them all into memory. I'm running into this very problem and was wondering whether the following would be feasible a)Detach the entity b)Create a new ObjectContext and attach the detached entity to i...