rdbms

问题 what is the use of decimal and numeric datatype in postgreSQL. As per the reference the following is the explanation given to these datatypes. Decimal,numeric --> It is a user specified precision, exact and range up to 131072 digits before the decimal point and up to 16383 digits after the decimal point. The above statement shows the description of decimal and numeric datatype. But, still I didn't understand what is the exact use of these data type and where it is used instead of other

问题 Simple question, could I conceivably use redis instead of mysql for all sorts of web applications: social networks, geo-location services etc? 回答1: Nothing is impossible in IT. But some things might get extremely complicated. Using key-value storage for things like full-text search might be extremely painfull. Also, as far as I see, it lack support for large, clustered databases: so on MySQL you have no problems if you grow over 100s of Gb in Database, and on Redis... Well, it will require

问题 I wonder how Object Oriented data modeling is different from Object Relational data modeling? Is it something like the pluses of both object oriented and relational data modeling were clubbed to achieve object relational data modeling? cheers 回答1: Object-Relational data modeling supports some object-oriented concepts, while still supporting some relational concepts: Inheritance -- one table can have an IS-A relationship with another table. Likewise custom data types support inheritance.

问题 I recently switched from Postgres to Solr and saw a ~50x speed up in our queries. The queries we run involve multiple ranges, and our data is vehicle listings. For example: "Find all vehicles with mileage < 50,000, $5,000 < price < $10,000, make=Mazda..." I created indices on all the relevant columns in Postgres, so it should be a pretty fair comparison. Looking at the query plan in Postgres though it was still just using a single index and then scanning (I assume because it couldn't make use

问题 I have a table Users (simplified) : UserId (int, PK) | Username | PasswordHash | LastVisitTimestamp Every time user visits a web site, LastVisitTimestamp column is updated. Is it a good idea to move that column into a separate table, so that timestamp updates do not lock entire row (actual row is bigger than presented here). I did that because I was frequently getting "row modified" exception when updating user information (result of update with optimistic concurrency). Or is there a better

问题 I am trying to map a existing relational database to a key value store. Couple of example tables are represented below. For an instance the above "Employee Details" table can be represented as follows in Redis (or any similiar key-value store) set emp_details.first_name.01 "John" set emp_details.last_name.01 "Newman" set emp_details.address.01 "New York" set emp_details.first_name.02 "Michael" set emp_details.last_name.02 "Clarke" set emp_details.address.02 "Melbourne" set emp_details.first

问题 It happened to me when I was reading about PostgreSQL on its wiki page where it refers to itself as an ORDBMS. I always knew about Microsoft SQL Server which is an RDBM system. Can someone help me understand the main differences between Relational Database Management System(RDBMS) and Object Relational Database Management System (ORDBMS) and in what scenarios should I use one of them? Also, my key question is related to the fact that in the world of Microsoft SQL Server we often use a layer

问题 It happened to me when I was reading about PostgreSQL on its wiki page where it refers to itself as an ORDBMS. I always knew about Microsoft SQL Server which is an RDBM system. Can someone help me understand the main differences between Relational Database Management System(RDBMS) and Object Relational Database Management System (ORDBMS) and in what scenarios should I use one of them? Also, my key question is related to the fact that in the world of Microsoft SQL Server we often use a layer

问题 I am working on an online survey. Most questions have a scale of 1-5 for an answer. If we need to add a question to the survey, I use a simple web form, which does an INSERT into the appropriate table, and voila! surveys are asking the new question -- no new code or change to the database structure. We are being asked to add survey questions that can have answers of different data types. The spec is to have the survey 'configurable', so that at any point in the future, when someone says, "We

问题 I have read some concept about time-series database and some answers about the differences between these 2 but I can't still get my head around these differences. How data is written and stored to disk that make the differences between time-series database and rdbms? What are the best use cases for time-series database over rdbms and VICE VERSA?. I mean the cases that make the time-series database provide outstanding performance over rdbms, also I want to know the cases that rdbms is a more