{"id":459,"date":"2023-01-25T13:36:07","date_gmt":"2023-01-25T13:36:07","guid":{"rendered":"http:\/\/learnlearn.uk\/ibcs\/?page_id=459"},"modified":"2023-01-25T13:36:07","modified_gmt":"2023-01-25T13:36:07","slug":"database-definition-language-queries","status":"publish","type":"page","link":"https:\/\/learnlearn.uk\/ibcs\/database-definition-language-queries\/","title":{"rendered":"Database Definition Language Queries"},"content":{"rendered":"
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Introduction<\/h2>\n
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What is a Database Definition Language?<\/h3>\n

This is the programming language used to construct and alter the design of tables contained within a database. The most common form of DDL is Structured Query Language(SQL).<\/p>\n

This language is not used to directly alter the data stored within a table, rather it is used to construct the framework within which data is contained – this type of data that is used to define other data is known as metadata<\/strong> – data about data.<\/p>\n

 <\/p>\n\n<\/div>

CREATE DATABASE<\/h2>\n
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Creating a Database – CREATE DATABASE<\/h3>\n

The syntax to create a database in SQL is simple:<\/p>\n

CREATE<\/span>\u00a0DATABASE<\/span>\u00a0databasename<\/em>; e.g.\u00a0CREATE<\/span>\u00a0DATABASE<\/span>\u00a0library.db<\/i><\/p>\n

To do the same in SQLite then you would use the shell command<\/p>\n

sqlite3 library.db\u00a0 <-\u00a0 if library.db already exists it will open the database, otherwise it will create it.<\/p>\n

 <\/p>\n\n<\/div>

CREATE TABLE<\/h2>\n
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Creating a Table – CREATE TABLE<\/h3>\n

Example 1 – Simple Non Relational Table<\/strong><\/p>\n

CREATE TABLE users(firstname varchar(255), lastname varchar(255), age integer, dateofbirth date);<\/p>\n

Example 2 – Create a table with a primary key<\/strong><\/p>\n

CREATE TABLE Orders (OrderID integer NOT NULL PRIMARY KEY, OrderNumber integer NOT NULL, CustomerID integer FOREIGN KEY REFERENCES Customers(CustomerID));<\/p>\n

 <\/p>\n

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SQL Data Types<\/strong><\/p>\n