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Introduction to databases

What is persistence?

As defined by wikipedia:

persistence refers to the characteristic of state that outlives the process that created it

What is a database?

The thing you keep your data in... or, an organized collection of data.

Several popular paradigms:

  • Relational (RDB)
  • Document
  • Key-Value
  • Object
  • Graph, etc.

RDB

A relational database consists of structured data, organized in tables. These tables have relationships with one another and are formally described. Data is stored in rows and columns.

Schema – A representation of the structure of a database. It may be graphical or textual.

Table – A collection of closely related columns. A table consists of rows each of which shares the same columns but vary in the column values.

Column – A single unit of named data that has a particular data type. Columns only exist in tables.

Row – One set of related values for all of the columns declared in a given table. Also known as a record.

Primary Key – A column or group of columns in a given table that uniquely identify each row of the table.

Foreign Key – One or more columns in a table intended to contain only values that match the related primary/unique key column(s) in the referenced table.

What is SQL?

Structured Query Language

The language of relational databases.

SQL Statements are divided into two primary categories:

  • DDL: Data Definition Language
    • Create, Drop, Alter, etc.
  • DML: Data Manipulation Language
    • Select, Insert, Update, Delete, etc.