The logical model and/or physical design of a database.

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1answer
281 views

Conversion of simple ERD to Table: is the solution below any good?

Consider the following ERD: Suppose that all entities only have two attributes: a PK plus a name/number. I want to convert that ERD to tables. Is it needed 4 tables (1 for each relationship ...
1
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1answer
521 views

Unique constraint to enforce max one null per item

I am using PostgreSQL 9.3. Suppose we are manufacturing some items of certain types, at any moment we are producing at most one item of a certain type. The following table captures our history of ...
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3answers
370 views

Heterogeneous ordered list of value

I have the following object model: class A { List<Thing> orderedListOfThings; } interface Thing { } class X implements Thing { int attr; } class Y implements Thing { String ...
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1answer
1k views

3NF Decomposition - I'm not sure about this example

I am trying to make sense of an example of 3NF decomposition using the 4-step algorithm mentioned by Ullman here, but I'm not understanding what my lecturer is doing with the last step (or, worse, I'm ...
1
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1answer
271 views

What is the advantages of using auto_increment in database as primary key over set of attributes?

I have table as CREATE TABLE circle ( circle_id int(11) auto_increment primary key not null, user_id int (11) not null, title varchar(255) collate utf8_general_ci not null ); CREATE ...
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1answer
222 views

Entity ID field that can refer to multiple tables?

In designing both audit tables and notification tables, I've run into an issue where I need a row to refer to an entity in another table, but which table that entity is isn't always the same. For ...
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1answer
1k views

Select rows from table where each row refers to a different schema

I have customer table in public schema. And I have a schema named after each customer. Each customer schema contains different tables like portals, plugin, ... When I want to select portals used by ...
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2answers
2k views

Which schema is better for a shopping project? [closed]

I'm working on a business-to-customer project that has variety of product types. There are a few properties like name, description, brand_id that each product has but there are also many specialized ...
0
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1answer
167 views

What are the first necessary actions needed to help secure a database's schema & data? [closed]

This smells like an open-ended, opinionated, wiki free-for-all, but I'm not trying to make this a battle of opinions. It seems like there should be a good checklist out there for all to agree on ...
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3answers
1k views

What is the optimal data type for an MD5 field?

We are designing a system that is known to be read-heavy (on the order of tens of thousands of reads per minute). There is a table names that serves as a sort of central registry. Each row has a ...
11
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2answers
421 views

Implementation of a many-to-many relationship with total participation constraints in SQL

How should I implement in SQL the scenario depicted in the following Entity-Relationship diagram? As it is shown, every A entity type occurrence must be related to at least one B counterpart (...
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4answers
2k views

How to store data in a database without tables?

All I learned in school was SQL which saves data to tables. Right now I am working on a project where data is stored in XML-files. Additionally every XML contains a reference to visual files (JPEG). ...
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4answers
1k views

Where should one put indexes in a time dimension table?

After reading the Questions and Answers from this website about indexes, a question came to my mind. What if, one is using a time dimension table with the lower level of granularity being the day. ...
9
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2answers
2k views

How does using separate schemas affect SQL Server 2008 performance?

I want to use separate schemas for objects with different purposes in our SQL Server 2008 database. Right now we use a fairly mind-numbing naming convention to indicate the purpose of a table or ...
8
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4answers
604 views

What are the performance considerations between using a broad PK vs a separate synthetic key and UQ?

I have several tables where records can be uniquely identified with several broad business fields. In the past, I've used these fields as a PK, with these benefits in mind: Simplicity; there are no ...
7
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4answers
1k views

How to create a database for unknown kinds of data?

I am in the process of designing a database for a new PHP/MySql-based application. My problem is that I do not and cannot represent what should be saved in the database because it is unlimited and ...
6
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2answers
15k views

Efficient way of changing VARCHAR to NVARCHAR fields in a large table in SQL Server 2008?

I am aware of when adding new fields to large tables, it is recommended to add them to the end of the fields rather than somewhere in the middle, and wondering if something like this applies when ...
6
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4answers
546 views

Purpose of IDs in a User Table Database

In a table, such as a user table, where there will only be 1 row with a for any particular user, why have an ID field, let alone as the primary key?
6
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2answers
179 views

Creating relationships between tables that where not specified in the given UML diagram

Good evening! I'm working on designing my very first actual database from the following UML class diagram (in French unfortunately): I'm at the point of creating the relational sketch of it which ...
6
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2answers
230 views

Is there a name for this “restricted one to many” relationship? Can it be enforced in the DB?

In an application I'm working on, we have a kind of "restricted one-to-many" relationship. I'm wondering if this has a name, and whether it's possible to enforce at the database level. A standard one-...
6
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1answer
89 views

Is my implementation of type/subtype design pattern (for mutually exclusive subclasses) correct?

Introduction In order for this question to be useful for future readers I will use the generic data model to illustrate the problems I face. Our data model consists of two entities, which shall be ...
5
votes
2answers
36k views

Using Same CASE WHEN Conditions For Multiple Query Columns

Is there a "better" way to rewrite a SELECT clause where multiple columns use the same CASE WHEN conditions so that the conditions are only checked once? See the example below. SELECT CASE ...
5
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2answers
4k views

What Is The Point of a Primary Key?

Why do I need to have a primary key on my database for it to function correctly? In every tutorial I read, you need to make the id key the primary key. What does the primary key do differently than ...
5
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2answers
254 views

Is there a reason/benefit I am not aware of for this kind setup?

I now manage a MySQL database that was designed and created by another. I am confused about a certain setup that the original developer created.. He did not use auto increments for table IDs. ...
5
votes
1answer
902 views

Enforce data integrity with a recursive table

I have an existing oracle 11g database schema that works with a web application. I am planning an expansion to the application so a web service can do data operations on the database. As part of the ...
5
votes
3answers
775 views

how do I model this in database?

I am using mysql as my backend database. Here is the use case; A HolidayPackage is configured with some default offerings. These default offerings can be up/downgraded based on the options provided. ...
4
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6answers
5k views

using IDENTITY column with increment -1

I need to run a sql server logging db with 2 main tables in 2 seperate datacentres writing to both at the same time. I had the idea of restoring the db to the new datacentre and then reseeding the ...
4
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1answer
769 views

SQLite3 simple database design question

I'm an ruby hobbist with no experience at all related to databases. I'm writing an application that is going to gather and backup tweets and blog posts (via rss feed) in an SQLite3 database. The ...
4
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3answers
5k views

indexes, foreign keys and optimization

Not a DBA so pardon my ignorance... I have a table with 20 fields of which 8 are foreign keys. Mysql has by default added an index for each foreign key. Table has about 100k rows. When retrieving ...
4
votes
3answers
192 views

SQL - Many-to-Many relationship with same table and with relationship constraint

I have a SellerProduct table. Each row within the table represents product information as offered by a seller. The SellerProduct table has the following columns: id (serial, pk) productName (nvarchar(...
4
votes
2answers
61 views

Does this simple database design work even if it's cyclic?

I am a graduate student working on breast cancer in a veterinarian facility. I am designing a database to keep track of the health of my mouse colony. Each day, animal care staff verify each cage ...
4
votes
1answer
3k views

Under what conditions are polymorphic associations used? What are the alternatives?

As I understand it, polymorphic relationships among tables in a database allow one table to have one foreign key that references many tables. I have found that tags are a common application of this ...
4
votes
2answers
115 views

What could justify a non explicit - non atomic primary key

I'm working as a "guest" dev at a random company. I'm working with a table that does not have a primary key by definition(Oracle). The column named "SOMETHING_ID" is varchar2(10) and constructed at ...
4
votes
1answer
183 views

Non-overlapping rectangles constrained to a boundary

I am trying to model placement of parts on a circuit board. Without any meaningful constraints, my basic schema looks like this: create table part ( part_id bigserial primary key, name text ...
4
votes
1answer
420 views

Storing phone number in E.164

TLDR; If I store a phone number in MySQL(or any DB with equivalent constraints), would the correct format be E.164 values into a VARCHAR(32) field? Have been reading up on format/storage of ...
3
votes
0answers
106 views

Inputting auto-incrementing, grouped, unique hashes?

Alright, here's what I've come up with so far: SET @id=(SELECT IFNULL(MAX(id) + 1, 0) FROM leads); UPDATE leads SET id=@id WHERE id IN ( SELECT id FROM (SELECT * FROM leads) AS something WHERE ...
3
votes
3answers
123 views

Schema for a lease platform

I have following tables: A room I want to lease (has user.id as ForeignKey) A users table for users who can rent it An availability table for time periods the room is to use with prices for that ...
3
votes
2answers
506 views

Is there a way I can speed up queries against this particular view?

I have three tables in a PostgreSQL database that I'm querying via a view and some joins. CREATE TABLE network_info ( network CIDR NOT NULL, some_info TEXT NULL, ...
3
votes
2answers
303 views

Deciding when to extend to child tables

I have a table of entities. For example purposes, lets call them Vehicles: Car, Boat, Motercycle, etc. I'd ideally like to place all entities in a single Vehicles table because a lot of related ...
3
votes
2answers
406 views

Database design for multiple user attributes

I am building an app with Laravel, and I have users which also have a profile. I am unsure about the best way to set up the database for the user attributes. For example: user_ud | name | ...
3
votes
2answers
339 views

Data Model For Summarizing Student Info

I work for a school district and one of the many things the admin wants to know is how many tardies a student has for a given time frame. I could certainly go retrieve the count from the attendance ...
3
votes
2answers
317 views

Use composite type to create new table

In ORDBMS databases I have seen that complex types can be used: create type name as( ...) And I can references those types when creating a new table, like: create table example (row_name ref(name))...
3
votes
3answers
176 views

Choosing a PK: VARCHAR(2) or SMALLINT(2)?

Today we were discussing the following: Brazil has 27 states and each one has its own abbreviation (just like USA). So we've got RJ for Rio de Janeiro, SP for São Paulo, MG for Minas Gerais and so on....
3
votes
2answers
248 views

Both Primary and Foreign Key Needed on Table?

Someone recently asked this question: There are two tables: Deal and DealCategories. One deal can have many deal categories. So the proper way should be to make a table called ...
3
votes
2answers
196 views

Simple table normalisation

In raw form, I have data with 2 columns: skills in welsh and stats for that skill. For storing these information in a database, would it be best to combine the stats with the categories, or split ...
3
votes
1answer
4k views

Two-column foreign key constraint only when third column is NOT NULL

Given the following tables: CREATE TABLE verified_name ( id SERIAL PRIMARY KEY, name TEXT NOT NULL, email TEXT NOT NULL, UNIQUE (name, email) ); CREATE ...
2
votes
2answers
457 views

Please review my first thought-out attempt at a database schema

I am researching database design and theory and have finally made a thoughtful attempt at creating a schema that would be based upon SQL. I would like, if someone has time, to review my layout and ...
2
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1answer
76 views

How to go about modeling the main object of relationship?

I'm using MySQL and MyISAM tables. I have a bunch of objects that I want to group together 1 object belongs to 1 and only 1 group 1 group can have many objects 1 group has 1 required main object ...
2
votes
3answers
240 views

Table naming and Database normalization

I'm creating a database of simulation results, and am trying to do so the right way. I've attempted to show relationships between data to make sure nothing redundant is thrown in. My current ...
2
votes
1answer
860 views

counter table in mysql

i was going through the book: High performance MySql 2nd edition. In chapter 4 it says: An application that keeps counts in a table can run into concurrency problems when updating the counters. ...