Information Systems

Candidate Key

A candidate key is a column, or set of columns, in a table that can uniquely identify any database record without referring to any other data. Each table may have one or more candidate keys, but one candidate key is unique, and it is called the primary key. This is usually the best among the candidate keys to use for identification.

SQL Composite Key

A composite key is a combination of two or more columns in a table that can be used to uniquely identify each row in the table when the columns are combined uniqueness is guaranteed, but when it taken individually it does not guarantee uniqueness. Sometimes more than one attributes are needed to uniquely identify an entity. A primary key that is made by the combination of more than one attribute is known as a composite key. In other words we can say that: Composite key is a key which is the combination of more than one field or column of a given table. It may be a candidate key or primary key. Columns that make up the composite key can be of different data types.

Determinant

A determinant in a database table is any attribute that you can use to determine the values assigned to other attribute(s) in the same row. Examples: Consider a table with the attributes employee_id, first_name, last_name and date_of_birth

Foreign key

A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. It acts as a cross-reference between tables because it references the primary key of another table, thereby establishing a link between them.

Primary key

A primary key, also called a primary keyword, is a key in a relational database that is unique for each record. It is a unique identifier, such as a driver license number, telephone number (including area code), or vehicle identification number (VIN). A relational database must always have one and only one primary key. Primary keys typically appear as columns in relational database tables.

Surrogate key

A surrogate key is any column or set of columns that can be declared as the primary key instead of a "real" or natural key. Sometimes there can be several natural keys that could be declared as the primary key, and these are all called candidate keys. So a surrogate is a candidate key.

SQL Alter Statement

ALTER TABLE table_name ALTER COLUMN column_name datatype;

Supertype

An entity type that has got relationship with one of more subtypes and it contains attributes that are common to its subtypes.

Subtypes

Are subgroups of the supertype entity and have unique attributes but they will be different from each subtype. https://learndatamodeling.com/blog/supertype-and-subtype/

Create SQL statement

CREATE TABLE table_name ( column1 datatype, column2 datatype, column3 datatype,

SQL DELETE Statement

DELETE FROM table_name WHERE condition;

Normalization

Database normalization is the process of organizing data into tables in such a way that the results of using the database are always unambiguous and as intended. Such normalization is intrinsic to relational database theory. It may have the effect of duplicating data within the database and often results in the creation of additional tables.

Denormalization

Denormalization is an approach to speeding up read-oriented data retrieval performance in a relational database, where the database administrator selectively adds back specific instances of redundant data after the data structure has been normalized. A denormalized database should not be confused with a database that has never been normalized.

Concept of Functional Dependency

Functional dependency is a relationship that exists when one attribute uniquely determines another attribute.

Insert SQL Statement

INSERT INTO Customers (CustomerName, ContactName, Address, City, PostalCode, Country) VALUES ('Cardinal', 'Tom B. Erichsen', 'Skagen 21', 'Stavanger', '4006', 'Norway');

Concept of Minimum cardinality

Min Cardinality(Optionality) Simply means "required." Its always 0 or 1. 0 would mean 0 or more, 1 ore more There are tons of good articles out there that explain this, including some that explain how to even property "diagram". Another thing you can search for is Cardinality/Optionality (OMG Terms) which explains the same thing, Optionality is "Min" Cardinality is "Max",

Null

Null (or NULL) is a special marker used in Structured Query Language to indicate that a data value does not exist in the database.

Database Management System

Organizations employ Database Management Systems (or DBMS) to help them effectively manage their data and derive relevant information out of it. A DBMS is a technology tool that directly supports data management. It is a package designed to define, manipulate, and manage data in a database. Designed to allow the definition, creation, querying, update, and administration of databases. Define rules to validate the data and relieve users of framing programs for data maintenance. Convert an existing database, or archive a large and growing one. Run business applications, which perform the tasks of managing business processes, interacting with end-users and other applications, to capture and analyze data.

Referential integrity constraint

Referential integrity is a property of data stating references within it are valid. In the context of relational databases, it requires every value of one attribute (column) of a relation (table) to exist as a value of another attribute (column) in a different (or the same) relation (table).

Concept of Maximum Cardinality

Remember cardinality is always a relationship to another thing. Max Cardinality(Cardinality) Always 1 or Many. Class A has a relationship to Package B with cardinality of one, that means at most there can be one occurance of this class in the package. The opposite could be a Package has a Max Cardnality of N, which would mean there can be N number of classes Min Cardinality(Optionality) Simply means "required." Its always 0 or 1. 0 would mean 0 or more, 1 ore more There are tons of good articles out there that explain this, including some that explain how to even property "diagram". Another thing you can search for is Cardinality/Optionality (OMG Terms) which explains the same thing, Optionality is "Min" Cardinality is "Max",

SQL UPDATE Statement

UPDATE table_name SET column1 = value1, column2 = value2, ... WHERE condition;