SQL
Relational Databases Table column/row All data
A relational database is a database that organizes information into one or more tables. Here, the relational database contains one table. A table is a collection of data organized into rows and columns. Tables are sometimes referred to as relations. A column is a set of data values of a particular type. Here, id, name, and age are the columns. A row is a single record in a table. All data stored in a relational database is of a certain data type. Some of the most common data types are: INTEGER, a positive or negative whole number TEXT, a text string DATE, the date formatted as YYYY-MM-DD REAL, a decimal value
Create
CREATE statements allow us to create a new table in the database. You can use the CREATE statement anytime you want to create a new table from scratch. The statement below creates a new table named celebs. CREATE TABLE celebs ( id INTEGER, name TEXT, age INTEGER); 1. CREATE TABLE is a clause that tells SQL you want to create a new table. 2. celebs is the name of the table. 3. (id INTEGER, name TEXT, age INTEGER) is a list of parameters defining each column, or attribute in the table and its data type: id is the first column in the table. It stores values of data type INTEGER name is the second column in the table. It stores values of data type TEXT age is the third column in the table. It stores values of data type INTEGER
SELECT
SELECT statements are used to fetch data from a database. In the statement below, SELECT returns all data in the name column of the celebs table. SELECT name FROM celebs; 1. SELECT is a clause that indicates that the statement is a query. You will use SELECT every time you query data from a database. 2. name specifies the column to query data from. 3. FROM celebs specifies the name of the table to query data from. In this statement, data is queried from the celebs table. You can also query data from all columns in a table with SELECT. SELECT * FROM celebs; * is a special wildcard character that we have been using. It allows you to select every column in a table without having to name each one individually. Here, the result set contains every column in the celebs table. SELECT statements always return a new table called the result set.
SQL, Structured Query Language
SQL, Structured Query Language, is a programming language designed to manage data stored in relational databases. SQL operates through simple, declarative statements. This keeps data accurate and secure, and helps maintain the integrity of databases, regardless of size. The SQL language is widely used today across web frameworks and database applications. Knowing SQL gives you the freedom to explore your data, and the power to make better decisions. By learning SQL, you will also learn concepts that apply to nearly every data storage system. The statements covered in this course use SQLite Relational Database Management System (RDBMS). You can also access a glossary of all the SQL commands taught in this course.
INSERT INTO
The INSERT statement inserts a new row into a table. You can use the INSERT statement when you want to add new records. The statement below enters a record for Justin Bieber into the celebs table. INSERT INTO celebs (id, name, age) VALUES (1, 'Justin Bieber', 22); 1. INSERT INTO is a clause that adds the specified row or rows. 2. celebs is the name of the table the row is added to. 3. (id, name, age) is a parameter identifying the columns that data will be inserted into. 4. VALUES is a clause that indicates the data being inserted. (1, 'Justin Bieber', 22) is a parameter identifying the values being inserted. ►1 is an integer that will be inserted into the id column ►'Justin Bieber' is text that will be inserted into the name column ►22 is an integer that will be inserted into the age column
Statements
The code below is a SQL statement. A statement is text that the database recognizes as a valid command. Statements always end in a semicolon ;. CREATE TABLE table_name ( column_1 data_type, column_2 data_type, column_3 data_type); Let's break down the components of a statement: 1.) CREATE TABLE is a Clause. Clauses perform specific tasks in SQL. By convention, clauses are written in capital letters. Clauses can also be referred to as commands. 2.) table_name refers to the name of the table that the command is applied to. 3.) (column_1 data_type, column_2 data_type, column_3 data_type) is a parameter. A parameter is a list of columns, data types, or values that are passed to a clause as an argument. Here, the parameter is a list of column names and the associated data type. The structure of SQL statements vary. The number of lines used does not matter. A statement can be written all on one line, or split up across multiple lines if it makes it easier to read. In this course, you will become familiar with the structure of common statements.
USE
This keyword pulls the a selected database.
FROM
this key word usually follows SELECT, pulls a selected
