Introduction to SQL english ebook

Introduction toI Structured Query Language I Usually “talk” to a database server I Used as front end to many databases mysql,postgresql, oracle, sybase I Three Subsystems: data descripti

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SQL

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Introduction to

I Structured Query Language

I Usually “talk” to a database server

I Used as front end to many databases (mysql,postgresql, oracle, sybase)

I Three Subsystems: data description, data access andprivileges

I Optimized for certain data arrangements

I The language is case-sensitive, but I use upper casefor keywords

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Introduction to

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Introduction to

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SQL What is SQL?

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Introduction to

I Multiple simultaneous changes to data (concurrency)

I Data changes on a regular basis

I Large data sets where you only need someobservations/variables

I Share huge data set among many people

I Rapid queries with no analysis

I Web interfaces to data, especially dynamic data

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Introduction to

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Introduction to

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Introduction to

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Introduction to

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Introduction to

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SQL When do you need a Database?

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I Backends to web sites

I Traditional rules may not be as important

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Introduction to

I console command (mysql -u user -p dbname)

I GUI interfaces are often available

I Interfaces to many programming languages: R,python, perl, PHP, etc

I SQLite - use SQL without a database server

I PROC SQL in SAS

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Introduction to

I PROC SQL in SAS

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Introduction to

I PROC SQL in SAS

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Introduction to

I PROC SQL in SAS

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Introduction to

I PROC SQL in SAS

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SQL Ways to Use SQL

I PROC SQL in SAS

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Introduction to

I A database server can contain many databases

I Databases are collections of tables

I Tables are two-dimensional with rows (observations)and columns (variables)

I Limited mathematical and summary operationsavailable

I Very good at combining information from severaltables

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SQL Some Relational Database Concepts

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Introduction to

Since a single server can support many databases, eachcontaining many tables, with each table having a variety

of columns, it’s easy to get lost when you’re working withdatabases These commands will help figure out what’savailable:

I SHOW DATABASES;

I SHOW TABLES IN database;

I SHOW COLUMNS IN table;

I DESCRIBE table; - shows the columns and theirtypes

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I SHOW DATABASES;

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I SHOW DATABASES;

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Introduction to

I SHOW DATABASES;

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SQL Finding Your Way Around the Server

I SHOW DATABASES;

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I INTEGER, SMALLINT, BIGINT

I NUMERIC(w,d), DECIMAL(w,d) - numbers with width

w and d decimal places

I REAL, DOUBLE PRECISION - machine and databasedependent

I FLOAT(p) - floating point number with p binarydigits of precision

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SQL Variable Types

SQL supports a very large number of different formats forinternal storage of information

Numeric

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Character

I CHARACTER(L) - a fixed-length character of length L

I CHARACTER VARYING(L) or VARCHAR(L) - supportsmaximum length of L

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Character

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Character

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Character

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Character

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Character

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Character

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Character

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Character

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SQL Variable Types (cont’d)

Character

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Introduction to

Suppose we have data measured on the height and weight

of children over a range of ages The first step is deciding

on the appropriate variable types, and creating the tablewith the CREATE TABLE command

CREATE TABLE kids(id CHAR(6),

race SMALLINT,age DECIMAL(6,3),height DECIMAL(7,3),weight DECIMAL(7,3),sex SMALLINT);

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SQL CREATE TABLE statement

Suppose we have data measured on the height and weight

of children over a range of ages The first step is deciding

on the appropriate variable types, and creating the tablewith the CREATE TABLE command

CREATE TABLE kids(id CHAR(6),

race SMALLINT,age DECIMAL(6,3),height DECIMAL(7,3),weight DECIMAL(7,3),sex SMALLINT);

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Introduction to

We could now enter individual items with the INSERTcommand:

INSERT INTO kids VALUES(100011,2,10.346,

148.5,38.95,1);

This quickly gets tedious We can automate the processusing the LOAD DATA command:

LOAD DATA INFILE ’kids.tab’

INTO TABLE kidsFIELDS TERMINATED BY ’\t’;This will read an entire tab-separated file into thedatabase in one command

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Introduction to

148.5,38.95,1);

INTO TABLE kidsFIELDS TERMINATED BY ’\t’;

This will read an entire tab-separated file into thedatabase in one command

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SQL Entering observations into a table

148.5,38.95,1);

INTO TABLE kidsFIELDS TERMINATED BY ’\t’;

This will read an entire tab-separated file into thedatabase in one command

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Introduction to

In SQL, the WHERE clause allows you to operate on subsets

of a table The following comparison operators areavaiable:

I Usual logical operators: < > <= >= = <>

I BETWEEN used to test for a range

I IN used to test group membership

I Keyword NOT used for negation

I LIKE operator allows wildcards

_ means single character, % means anything

I SELECT salary WHERE name LIKE ’Fred %’;

I RLIKE operator allows regular expressions

I Use AND(&&) and OR(||) to combine conditions

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