denormalization

问题 i have a data state in redux store like: { 123: { a: 'abc' }, 456: { a: 'def' }, 789: { a: 'ghi' }, } this is an array of objects like: const trainersArray= [ { _id: 123, a: 'abc' }, { _id: 456, a: 'def' }, { _id: 789, a: 'ghi' }, ] export const trainer = new schema.Entity( 'trainers', {}, { idAttribute: '_id' } ); const { trainers: normalizedTrainers } = normalize(trainersArray, [ trainer, ]).entities; now i want to denormalize like below in a component but i just don't get it? const

问题 I am trying to get data from a YAML file into a Pandas DataFrame. Take the following example data.yml : --- - doc: "Book1" reviews: - reviewer: "Paul" stars: "5" - reviewer: "Sam" stars: "2" - doc: "Book2" reviews: - reviewer: "John" stars: "4" - reviewer: "Sam" stars: "3" - reviewer: "Pete" stars: "2" ... The desired DataFrame would look like this: doc reviews.reviewer reviews.stars 0 Book1 Paul 5 1 Book1 Sam 2 2 Book2 John 4 3 Book2 Sam 3 4 Book2 Pete 2 I've tried feeding the YAML data to

问题 I am trying to get data from a YAML file into a Pandas DataFrame. Take the following example data.yml : --- - doc: "Book1" reviews: - reviewer: "Paul" stars: "5" - reviewer: "Sam" stars: "2" - doc: "Book2" reviews: - reviewer: "John" stars: "4" - reviewer: "Sam" stars: "3" - reviewer: "Pete" stars: "2" ... The desired DataFrame would look like this: doc reviews.reviewer reviews.stars 0 Book1 Paul 5 1 Book1 Sam 2 2 Book2 John 4 3 Book2 Sam 3 4 Book2 Pete 2 I've tried feeding the YAML data to

问题 When it comes to denormalizing data in a transactional database for performance, there are (at least) three different approaches: Push updates through stored procedures which update both the normalized transactional data and the denormalized reporting/analysis data; Implement triggers on the transactional tables that update the secondary tables; this is almost always the route taken when maintaining histories; Defer the processing to a nightly batch process, possibly doing an ETL into a data

问题 Overview (Sorry its vague - I think if I went into more detail it would just over complicate things) I have three tables, table one contains an id, table two contains its own id and table one's id and table three contains its own id and table two's id. I have spent a lot of time pondering and I think it would be more efficient for table three to also contain the related table ones id. -It will mean I will not have to join three tables, I can just query table three (for a query that will be

问题 Overview (Sorry its vague - I think if I went into more detail it would just over complicate things) I have three tables, table one contains an id, table two contains its own id and table one's id and table three contains its own id and table two's id. I have spent a lot of time pondering and I think it would be more efficient for table three to also contain the related table ones id. -It will mean I will not have to join three tables, I can just query table three (for a query that will be

问题 I need to separate the following array data but can't think of a good and quick way to do it. Name OrderGroup OrderDate PID365583 FY13Q1-D 8/28/2014 12:00:00AM PID354731,361935 FY13Q2-D 8/28/2014 12:00:00 AM PID354737,361937 FY13Q3-D 11/7/2014 12:00:00 AM PID359099,361933,363165 FY13Q4-D 11/13/2014 12:00:00 AM Every name that has more than one number associated with it (separated by commas) I need to move to a separate line in the array and copy the same info from the array line that it's

问题 Seems like a blog with comments is the standard example used for describing different modeling strategies when using MongoDB. My question relates to the model where comments are modeled as a sub collection on a single blog post document (i.e one document stores everything related to a single blog post). In the case of multiple simultaneous writes it seems like you would avoid overwriting previous updates if you use upserts and targeted update modifiers (like push). Meaning, saving the

问题 I read that in nosql (cassandra for instance) data is often stored denormalized. For instance see this SO answer or this website. An example is if you have a column family of employees and departments and you want to execute a query: select * from Emps where Birthdate = '25/04/1975' Then you have to make a column family birthday_Emps and store the ID of each employee as a column. So then you can query the birthday_Emps family for the key '25/04/1975' and instantly get all the ID's of the

问题 What are the best practices for database design and normalization for high traffic websites like stackoverflow? Should one use a normalized database for record keeping or a normalized technique or a combination of both? Is it sensible to design a normalized database as the main database for record keeping to reduce redundancy and at the same time maintain another denormalized form of the database for fast searching? or Should the main database be denormalized but with normalized views at the