Northwind2003 database 11 Aug

Sakila database 11 Aug

3 MySQL server Relational database management program Administer relational database Update database information Extract information through queries Server-client architecture User authentication Competitors: Access, Oracle, PostgreSQL 3

11 Aug MySQL client Personal program to access MySQL Command line interface HeidiSQL Preconfigured portable version from course website 4

11 Aug Starting HeidiSQL 1. Uncompress it on your Desktop 2. Connect to alcor.inf.unibz.it 3. Type your unibz username and password To use it from outside unibz LAN, you need before to log in to VPN here Manually configuring HeidiSQL (not needed) Installing MySQL server on your computer (useful but not necessary) 5

11 Aug Using HeidiSQL Database structure in the left window Commands executed and errors in the log window below Queries can be written in the Query tab and executed pressing F9 or Highlighting some commands and pressing F1 activates the SQL help 6

11 Aug Using HeidiSQL USE {database}; or click in the left window You must have appropriate privileges: GRANT SELECT GRANT INSERT GRANT UPDATE GRANT DELETE GRANT ALTER No way to undo your changes!!! ROLLBACK; command does not work on most MySQL tables 7

Selection query 11 Aug A question which produces a temporary table SELECT fields FROM table; SELECT fields FROM table WHERE condition ORDER BY field ASC|DESC; Mathematical operations AND, OR, NOT and parentheses Virtual field: expression AS name Views CREATE VIEW name AS selection query; DROP VIEW name;

Selection query 11 Aug mathematical operators + - * / and comparisons = = <> ROUND( ), ABS( ), EXP( ), SQRT( ), LOG( ) condition1 AND condition2, condition1 OR condition2, NOT condition field BETWEEN value1 AND value2 IS NULL, IS NOT NULL field IN (list) field LIKE expression containing % or _ CURDATE(), DATE_ADD(date, INTERVAL number DAY|MONTH|YEAR) YEAR(date), MONTH(date), DAY(date) DATEDIFF(date2,date1) To get difference in years: Approximate: ROUND(DATEDIFF(date2,date1)/365.25) Exact: YEAR(date2) - YEAR(date1) - ( DATE_FORMAT( date2, '%m%d' ) < DATE_FORMAT( date1, '%m%d' ) )

Joins 11 Aug Inner join SELECT fields FROM table1 INNER JOIN table2 ON field1 = field2; Names containing spaces must be enclosed by grave accent ` Values enclosed instead by apostrophe ’ Ambiguous field names use table.field table AS shortname from now on you must use nickname Difference between WHERE and ON Cross join Multiple inner joins

Summary query 11 Aug aggregates the records based on a GROUP BY instruction and returns one record per distinct value of GROUP BY fields If no GROUP BY is inserted, it aggregates everything SELECT function(field), grouping fields FROM tables with inner joins GROUP BY field; function is an aggregating function: Sum(field), Avg(field), Max(field), Min(field) Count(*), Count(DISTINCT field)

Summary query 11 Aug Conditions WHERE condition filters (and is written) before aggregation and thus must be used on fields which disappears after aggregation HAVING condition filters (and is written) after aggregation and thus must be used on aggregating functions fields which exist before and after aggregation, such as grouping fields, can be used in both conditions equivalently Do not select extra fields in summary queries!

Modifying data 11 Aug Using HeidiSQL graphical interface TRUNCATE table; DELETE FROM table WHERE condition; UPDATE table SET field = value WHERE condition; INSERT INTO table (fields) VALUES (values), …, (values); Exporting text data Fields’ delimiter Values’ encloser Importing text data Prepare structure before 13

Field types 11 Aug INT -2 billions to 2 billions TINYINT 0 or 1 DECIMAL(total number of digits, number of decimal digits) FLOAT non-exact real number CHAR (number of characters) fixed length text VARCHAR(maximum number of characters) variable length text TEXT very long text up to 60,000 characters ENUM( value, …, value ) Pay attention to numbers DATE time is supposed to be midnight, DATETIME Options NOT NULL, AUTO_INCREMENT, UNIQUE, DEFAULT default value, INDEX Primary key automatically has UNIQUE and NOT NULL and is an index Numerical codes are not numbers!

Table 11 Aug CREATE TABLE table ( field field-type options, …, PRIMARY KEY (field), INDEX (field), CHECK (condition) ); DROP TABLE table; ALTER TABLE table ADD field field-type options; ALTER TABLE table DROP field; ALTER TABLE table ADD PRIMARY KEY field; ALTER TABLE table DROP PRIMARY KEY; Using MySQL graphical interface Steal code from another table

 Create a blank database ◦ Build the tables  Start from the tables on the “1” side  Put appropriate types  Put appropriate primary key ◦ Check the structure ◦ Fill in the tables 16 Home exercise: Your library

 Queries ◦ Build a query to show book title, author surname, publishing year and author birth date ◦ Build a query to show book title, author surname and publishing date only for German and French authors.  Do not rewrite a new one. Modify easily the previous one adding another field with a condition and hiding it ◦ Build a query to show book title, author surname and publishing date only for those book published before  Do not rewrite a new one. Modify the first one. 17 Home exercise : Your library

 Exercises ◦ Is there the book TITLE? ◦ Is there a book TITLE published after 1/1/2000? ◦ Which books AUTHOR has published?  Improvements ◦ Put NOT NULL for appropriate fields ◦ Insert check constraints for appropriate fields ◦ Build a structure for predefined values lists where appropriate 18 Home exercise : Your library

 Advanced queries. Build a query which: ◦ shows book title, author surname and publishing year only for those authors born before a date invented by you. ◦ shows book title, author surname and the age of the author when the book was published. ◦ counts the books for every author. ◦ calculates the average publishing year of each author ◦ calculates the average publishing year of each author considering only German and English authors. 19 Home exercise : Your library

 Build a blank database ◦ Build the tables  Start from the tables on the “1” side  Put appropriate types  Put appropriate primary keys ◦ Check the structure ◦ Fill in the tables 20 Home exercise : students and exams

 Queries ◦ Build a query which displays, for every student, the list of his passed exams. ◦ Build a query which displays the list of passed exams and students’ last names, considering only who got a laude. ◦ Build a query which displays the student number (ordered from lowest to highest) of students who passed computer science. 21 Home exercise : students and exams

◦ Expand the database inserting information about professors and their exams  Many to many relation  another extra table ◦ Put NOT NULL for appropriate fields ◦ Insert check constraints for appropriate fields ◦ Build a structure for predefined values lists where appropriate 22 Home exercise : students and exams

 Advanced queries. Build a query which: ◦ shows the list of courses of professor Coletti. ◦ shows the list of exams of professor Coletti with the average grade that students obtain in the exam (considering, obviously, only the passed attempts) ◦ shows the list of professor Coletti’s exams with the number of students who got more that Home exercise : students and exams