Βασικές πληροφορίες που αφορούν την αποθήκευση και την ανάκτηση των δεδομένων μας στον Ηλεκτρονικό Υπολογιστή, μέσω των εφεδρικών αρχείων ασφάλειας (backups) αλλά και των ενσωματωμένων δυνατοτήτων των Windows (backup - restore points - κλπ).
Βασικές πληροφορίες που αφορούν την αποθήκευση και την ανάκτηση των δεδομένων μας στον Ηλεκτρονικό Υπολογιστή, μέσω των εφεδρικών αρχείων ασφάλειας (backups) αλλά και των ενσωματωμένων δυνατοτήτων των Windows (backup - restore points - κλπ).
The document outlines the features and tools available in an online school administration system, including a document repository, calendar, and forums for communication. It also describes how the system allows administrators to set up and maintain school data and define relationships between entities, while providing three levels of access rights. A flexible and easy-to-use calendar is included along with contact information.
This document describes Webclass.eu, an online learning management system that allows teachers to organize and deliver course content to students. It discusses the system's features like forums, calendars, and document access controls. The technology uses a Java web application with MySQL and Tomcat. Future releases may include online exercises, auto-grading, chat functions, and encrypted document viewing. Subscription schemes are available for individual teachers, schools, and private installations with different support and training options.
This document outlines the features and tools available in an online learning platform, including setup and maintenance of teacher profiles, defining student groups, creating course templates, accessing course content, using collaboration tools like document sharing and forums, and customizing user access permissions. The platform aims to provide a flexible set of features to facilitate the educational process both for teachers and students.
This document describes an online learning platform that provides courses, document repositories, calendars, forums, and other tools to aid the educational process. It allows each student private access to only the courses they are enrolled in, where they can add their own materials. The platform also offers flexible calendars and three levels of access rights for content.
This document describes an online learning platform that provides courses, document repositories, calendars, forums and other tools to aid the educational process. It allows each student private access to only the courses they are enrolled in. The platform also offers 3 levels of access rights and a flexible calendar. Contact information and the website URL are provided at the end.
The document outlines the features and tools available in an online school administration system, including a document repository, calendar, and forums for communication. It also describes how the system allows administrators to set up and maintain school data and define relationships between entities, while providing three levels of access rights. A flexible and easy-to-use calendar is included along with contact information.
This document describes Webclass.eu, an online learning management system that allows teachers to organize and deliver course content to students. It discusses the system's features like forums, calendars, and document access controls. The technology uses a Java web application with MySQL and Tomcat. Future releases may include online exercises, auto-grading, chat functions, and encrypted document viewing. Subscription schemes are available for individual teachers, schools, and private installations with different support and training options.
This document outlines the features and tools available in an online learning platform, including setup and maintenance of teacher profiles, defining student groups, creating course templates, accessing course content, using collaboration tools like document sharing and forums, and customizing user access permissions. The platform aims to provide a flexible set of features to facilitate the educational process both for teachers and students.
This document describes an online learning platform that provides courses, document repositories, calendars, forums, and other tools to aid the educational process. It allows each student private access to only the courses they are enrolled in, where they can add their own materials. The platform also offers flexible calendars and three levels of access rights for content.
This document describes an online learning platform that provides courses, document repositories, calendars, forums and other tools to aid the educational process. It allows each student private access to only the courses they are enrolled in. The platform also offers 3 levels of access rights and a flexible calendar. Contact information and the website URL are provided at the end.
3. Indices (=ευρετήρια ή δευτερεύοντα κλειδιά)
Επιταχύνουν τη διαδικασία ανάκτησης των επιθυμητών δεδομένων
Δημιουργούμε σε στήλες τις οποίες χρησιμοποιούμε συνέχεια για αναζήτηση δεδομένων
Η προσθήκη ευρετηρίων πρέπει να γίνεται με σύνεση γιατί μπορεί να δημιουργήσει
σοβαρά προβλήματα, όπως
◦ η χρήση υπερβολικού αποθηκευτικού χώρου
◦ μεγάλος φόρτος εργασίας στη βάση αφού κάθε νέα καταχώρηση στον πίνακα απαιτεί την
ανανέωση ή και ταξινόμηση του ευρετηρίου.
3
sid name semeste
r
age did
121 Steve A 33 1
145 Graham B 45 1
646 Yanis A 37 2
756 Pye B 28 2
152 George B 33 1
sid
121
145
152
646
756
4. Δημιουργία Index
1. create table table_name(column1 column1_type, column2 column2_type, ……, index
index_name (column_name1, column_name2,…), index index_name(…),…);
2. create index index_name on table_name (column_name);
Παράδειγμα: create index schoolNameInd on school(name);
3. alter table table_name add index (column_name);
Παράδειγμα: alter table school add index(name);
Διαγραφή Index
1. drop index schoolNameInd on school;
2. alter table school drop index schoolNameInd;
4
5. Το foreign key είναι λογικός περιορισμός.
Η προκαθορισμένη μηχανή αποθήκευσης MyIsam έχει πολύ μεγάλη ταχύτητα,
αλλά δεν υποστηρίζει τα foreign keys.
show table status;
Alter table table_Name ENGINE=InnoDB;
Δοκιμάστε να προσθέσετε την παρακάτω εγγραφή στον πίνακα dept
insert into dept(did, name, scid) values(100, 'cs2‘, 512);
Τι παρατηρείτε?
5
6. Δημιουργία foreign key
1. create table table_name1(column1 column1_type, column2 column2_type, ……, foreign
key (column_name) references table_name2 (column_name) on delete cascade)
2. alter table table_name1 add foreign key (column_name) references table_name2
(column_name) on delete cascade;
3. alter table table_name1 add constraint constraint_name foreign key (column_name)
references table_name2 (column_name) on delete cascade;
3. Κάνετε foreign key το πεδίο που συνδέει τους πίνακες school και dept
alter table dept add foreign key(scid) references school(scid)
on delete cascade;
Ο όρος “on delete cascade” είναι προαιρετικός και λέει στη βάση ότι όταν σβηστεί
ένα πεδίο από τον πίνακα school, θα σβηστούν και τα αντίστοιχα πεδία από τον πίνακα
dept.
6
7. Δοκιμάστε τώρα να καταχωρήσετε την εγγραφή
insert into dept(did, name, scid) values(101, 'cs3‘, 1025);
Τι παρατηρείτε?
Διαγραφή foreign key
Για να διαγράψουμε το Foreign key πρέπει να ξέρουμε το όνομά του. Η
show create table dept;
επιστρέφει την εντολή “create table” που θα χρησιμοποιούσαμε
για να δημιουργήσουμε τον πίνακα dept στην τρέχουσα κατάστασή του, από όπου
μπορούμε να δούμε το όνομα που έχει δοθεί στο foreign key.
alter table table_name drop foreign key fkeyΝame;
Παράδειγμα: alter table dept drop foreign key fKeyName;
ΑΣΚΗΣΗ: Κάνετε foreign key το πεδίο που συνδέει τους πίνακες
dept και student
7
Foreign keys(3)Foreign keys(3)