rdbms

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 4 years ago . I'm looking at implementing an RDBMS. Are there any good resources out there about how a database works internally, and the kinds of things I'd need to know when starting out to build my own? (Please no comments about whether it's a practical idea or not - just imagine it's for a hobby project or something).

问题 I've always considered that there were no isolation within a single transaction. For example if I have 2 methods M1 and M2, M1 update X in database and M2 select X or a set containing X. If both method belongs to the same transaction and M2 is executed after M1: Does M2 always seen M1 update whatever the type of operation, the RDBMS or the isolation level is ? If no, can someone explain in details the different possible behavior according to associated criteria 回答1: In the situation described

问题 I have seen many examples about fully functional dependencies, but they use to say that: x->y such that y shouldn't be determined by any proper subset of x, x has to be a key. But, what if y is determined by an attribute other than the proper subset or subset of x. Suppose that I have a students table which consists of rollno(primary key), name, phone no unique not null, email unique not null. As rollno is a primary key, let it be x and take name as y. now x->y, but phone or email also

问题 As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance. Closed 7 years ago . I'm having difficulties to answer this question. Can someone help me? Discuss the benefits of MYSQL and explain why it is gaining

问题 I am using triggers for the first time. If I update a field in a table by an update trigger on the same table, with this spark a loop? Does sql server guard against this recursive behavior? Thanks 回答1: This page (search for RECURSIVE_TRIGGERS ) describes some of the database settings you can use to modify this behavior. Also, one way to safeguard your procedures is to use either the UPDATE() function or the COLUMNS_UPDATED() function. If, for example, you have a table with columns A , B , and

问题 The definition of schema is logical structure of data in database. It is owned by a user and has the same name as the database user. The schema contains name of table, what is it's column type etc. And the data dictionary also contains metadata only (offcourse it is at database level and not at user level). What is the exact difference between schema and data dictionary? 回答1: These definitions are from my experience (programmer for 20+ years, 7 years in consulting, some time as an independent

问题 I have a VB6 application accessing a single table on a MSSQL2000 server via ADO. I'm using read-only access (adOpenStatic, adLockReadOnly) There are other applications in the network which do make changes to the table. For some reason I'm getting errors about my application being chosen as a deadlock victim. I'm really confused: Why can there be a deadlock when I'm just reading from a single table? I'd expect timeouts, because of the writing of the other applications, but not a deadlock...

问题 Coming from question “Relation” versus “relationship” What are definitions of "relation" vs. "relationship" in RDBMS (or database theory)? Update: I was somewhat perplexed by comment to my question: "relation is a synonym for table, and thus has a very precise meaning in terms of the schema stored in the computer" Update2: Had I answered incorrectly that question , in terms of RDBMS, having written that relation is one-side direction singular connection-dependence-link, i.e. from one table to

问题 I have to store scheduled events, (like say class times, for example) that can be organized on a weekly, daily or monthly basis. Events can occur, say, every Monday and Wednesday, or every second Thursday of the month. Is there a way to store this information in an RDBMS that adheres to 3NF? EDIT: This is not homework; I'm building something with a friend for our own edification and we want it in 3NF. To be specific, I'm trying to store the schedules for mass and confession times at RC

问题 I have around 3500 flood control facilities that I would like to represent as a network to determine flow paths (essentially a directed graph). I'm currently using SqlServer and a CTE to recursively examine all the nodes and their upstream components and this works as long as the upstream path doesn't fork alot. However, some queries take exponentially longer than others even when they are not much farther physically down the path (i.e. two or three segments "downstream") because of the added