relational-database

I am trying to figure out the fastest way to access data stored in a junction object. The example below is analagous to my problem, but with a different context, because the actual dataset I am dealing with is somewhat unintuitive in its relationships. We have 3 classes: User , Product , and Rating . User has a many-to-many relationship to Product with Rating as the junction/'through' class. The Rating object stores the answers to several questions which are integer ratings on a scale of 1-5 (Example questions: How is the quality of the Product , how is the value of the Product , how user

I have a table with N columns. Let's call them c1 , c2 , c3 , c4 , ... cN . Among multiple rows, I want to get a single row with COUNT DISTINCT(cX) for each X in [1, N]. c1 | c2 | ... | cn 0 | 4 | ... | 1 Is there a way I can do this (in a stored procedure) without writing every column name into the query manually? Why? We've had a problem where bugs in application servers mean we rewrite good column values with garbage inserted later. To solve this, I'm storing the information log-structure, where each row represents a logical UPDATE query. Then, when given a signal that the record is

I'm trying to draw an ER diagram for my project management software describing the following. It contains these entities: project - software projects tasks - software projects that can be broken into a number of tasks employees - employees that belong to this software And: A project can be divided into tasks. (Tasks can be created by the admin user, who can assign those tasks to selected projects. Here there is only assignment of tasks to projects, not assignment of employees to projects.) Employees can be assigned to projects. (An employee can be assigned to projects. Here there is only

I am creating a database for the first time using Postgres 9.3 on MacOSX. Let's say I have table A and B . Table A starts off as empty and Table B as filled. I would like the number of entries in column all_names in table B to equal the number for each names in table A like table B below. Thus names should contain each unique entry from all_names and number its count. I am not used to the syntax yet so I do not really know how to go about it. The birthday column is redundant. A names | number -------+------------ Carl | 3 Bill | 4 Jen | 2 B all_names | birthday -------+------------ Carl | 17

Woocommerce v2.6 stores the following meta_key values in the wp_postmeta table: _sku _price _regular_price _sale_price _manage_stock _stock_status _featured Does Woocommerce v3.x, still store are all of the above in an identical manner as v2.6 or have any of the above been relocated to another table and/or modified in any way? In WooCommerce 3+ everything listed is the same, except for _featured that doesn't work any more. The " feature " product functionality in WooCommerce 3+: Since version 3, WooCommerce generates a featured term (name and slug) located in wp_terms table, which custom

I'm fairly new to database management and this question never seems to be answered in more than one sentence. All other SO answers say "A candidate key is a minimal super key." That means nothing to me. A candidate key is supposed to specify uniqueness of a db record, correct? And a primary key is a candidate key. If a primary key already specifies uniqueness, what's point of adding more candidate keys? I have seen example records like the following: Employee(ID, Name, PhoneNumber) where ID is the primary key and PhoneNumber is a candidate key. From what I see, the ID is enough to specify the

Basically I'd like to know the difference between using REFERENCES with or without a foreign key. I have these 2 examples: CREATE TABLE Employee ( id INT, name VARCHAR(50), birthYear INT, boss INT REFERENCES Employees(id), worksAt INT NOT NULL REFERENCES Department(id) ON DELETE CASCADE, PRIMARY KEY (id,worksAt) ); Example 2: CREATE TABLE Department ( id INT PRIMARY KEY, name VARCHAR(50), numberOfEmployees INT, location INT NOT NULL, country INT NOT NULL, manager INT, FOREIGN KEY (location,country) REFERENCES Location(locId,countryId), UNIQUE KEY (manager) ); What I'm asking here is why does