Relational database Basics

Introduction to Relational databases

Relational database is made up of tables, the database is managed by DBMS, DBMS is called database management system or database server. The database server supports a database language that is used to create and delete databases and to manage and search data. Almost all database servers use SQL: A set of statements that define and manipulate data. The most common SQL statements are: Insert,update,delete and select, respectively, for adding, changing, deleting, and searching data.

A database table may have different properties, the table contains data rows (row), and each row contains values for each property, which, together, is an associative object. An attribute (attribute) is also called a field or column (column), and a row of data is also known as a record. Trial unique values managing data associativity is the basis of a relational database. The unique value of a table or a primary key (primary key) is usually formed by a unique value that is sufficient to mark each record (possibly more than one), and the values of these fields may not be meaningful to the user, just a unique digital identification data record to maintain the data's relevance.

Entity Relationship (Entity-relationship,er) modeling shows the model of a sample database, which is a standard for visualizing a database and understanding relationships between tables. Er models are particularly well suited for more complex, associative types of databases, and we need to understand how to maintain the latest data and applications on queries.

Database terminology

Database (Datebase)

The warehouse where the data is stored. A database may store records related to a company's finances and so on.

Tables (table)

A part of a database that stores only data related to a single target, thing, and behavior. For example, a table might store customer data, a table of different fields (field, column, or attribute (attribute) is also a common name), stored in a data row (row, or record).

Fields (field)

The vertical data field in the table. Each row of data records has the same field. For example, there may be fields such as name,address,city in the client's table. Each field has its own data type, such as String, Integer, date, etc.

Records (record)

The data entity in the table. Each record contains values for each field, for example, in the table of customer data that may contain data such as "Matthew Richardson", "Punt Road", "Richmond", and records become rows.

Relational models (relational model)

A model that uses databases, tables, fields to store data, and to manage relationships between tables.

(relational) database management system (DBMS)

Manage the application software of the database, manage the data in the database and build on the relational model. Also becomes a database server. (Datebase server).

Sql

The standard query language used to interact with the database server. SQL is a set of statements that manage databases, tables, and data. Although it is thought that the pronunciation of SQL is sequel, it is the abbreviation of Structured Query Language (structured-Language), but SQL only needs to be read alphabetically.

Constraint (constraint)

Restrictions on tables and letters. Usually the database is made up of many constraint, for example: A brewery can only have one, no customer before there is no order, customer name is a column is required.

Primary key (primary key)

Used to uniquely mark individual records and one or more fields, such as the field Cust ID of the Customer table, which specifies a unique value for each customer. The constraint of most tables are primary key.

Indexing (Index)

is a quick access to the data structure recorded in the table. Indexes are usually indexed according to the primary key of each table, and are used to quickly find specific records. An index may also be defined or established by a field that is frequently used for queries.

Entity-Relationship model (entity-ralationship Model,er model)

A technique that uses entities, fields, and relationships to describe real data.

Normalized databases (normalized database)

A database designed according to the ER model. The specification also has different types or levels, and the third canonical form of the database is usually designed as an acceptable relational database.

Relational database Basics