Databases Using MySQL Creating Tables Queries

Databases  A database is a collection of data organized for efficient access  A relational database is a collection of tables  Columns represent attributes  Rows represent entities  Usually, want one attribute (primary attribute) to be unique

Sample Table dish_iddish_namepriceis_spicy 1Walnut Bun1.000

Sample Tables fnamelnameunamepasswd unameentrycomments tcoleLearning PHP 5book

Structured Query Language  A language create, query and modify relational databases.  SQL commands are not case-sensitive  table and column names are case sensitive in MySQL  White space is not critical  Strings are delimited by single quotes  SQL is not procedural - you specify what result you want not how to get to that result

MySQL  There are a number of database vendors  MySQL is a free database system  installed on onyx  Interacting with MySQL from a shell mysql -p -u php_user show databases \g use databaseName \g show tables \g source loadTables.sql \q

Programming with MySQL  Many programming languages have modules or libraries that support access to databases  perl has the DBI module  PHP has separate modules for each database type as well as the PEAR module which provides a uniform interface to all of them  Java has the JDBC API (java.sql)

Setting Up a Database  CREATE DATABASE databaseName;  USE databaseName;  CREATE TABLE tableName (col1 type1, col2 type2, …);  DROP DATABASE databaseName;  DROP TABLE tableName

Types for Attributes TypeDescription int(length)integer with maximum of length digits decimal(width[,decimal_digits])width is max digits datetimeYYYY-MM-DD HH:MM:SS timeHH:MM:SS dateYYYY-MM-DD timestampYYYYMMDDHHMMSS varchar(length)variable-length string char(length)fixed-length string blobup to 64K of data

Modifiers and Keys  NOT NULL for attribute that must be given a value  DEFAULT "value" to provide default value  int values can be labeled auto_increment to automatically generate unique numbers  PRIMARY KEY (columnName)  KEY keyName (colName1[,colName2])

Example 1 CREATE TABLE DISHES (dish_id INT, dish_name VARCHAR(255), price DECIMAL(4,2), is_spicy INT);

Modifying the Table Data  INSERT  UPDATE  DELETE

Inserting data  INSERT INTO tableName VALUES (v1, v2, …,vn);  use NULL as placeholder for missing values  can insert multiple rows at a time using comma-separated lists  INSERT INTO tableName SET cola=va, colb = vb;  provide values for all columns that can't be null  INSERT INTO tableName (cola, colb, …) VALUES (va, vb, …)

Deleting Data  DELETE FROM tableName;  removes all data from the table  DELETE FROM tableName WHERE colName=value;

Updating Data  UPDATE tableName SET col = value;  updates value of col for all rows in table  UPDATE tableName SET col = value WHERE col=value;  updates only rows which satisfy WHERE clause

Querying the database  SELECT * FROM tableName  show entire table  SELECT col1, col2 FROM tableName  show listed columns from tableName for all rows  SELECT * from tableName WHERE col=value  show rows that match selection criteria

Ordering and Grouping  SELECT * FROM tableName ORDER BY colName [DESC]  sort the rows  You can group rows with the same value in a particular column so that you can compute aggregate values (count, sum, avg, max, min)  SELECT colName, count(*) FROM tableName GROUP BY col2  Use HAVING with a condition to select groups for which an aggregate function meets a particular requirement

WHERE Clauses  WHERE clause limits the rows retrieved by specifying a condition that must be met  look for a particular value or range of values in some column  Use AND and OR to combine conditions  use LIKE for string matching

Things I left out  JOIN - sometimes you need to combine information from two or more tables in a single query.  You can use LIMIT to restrict the number of rows in the output  SELECT DISTINCT outputs a single copy of identical rows in the output

Sources  MySQL website   MySQL Visual Quickstart Guide by Larry Ullman  PHP and MySQL by Hugh E. Williams and David Lane