Geo-Databases: lecture 5 Data Manipulation in SQL Prof. Dr. Thomas H. Kolbe Institute for Geodesy and Geoinformation Science Technische Universität Berlin Credits: This material is mostly an english translation of the course module no. 8 (‘Geo-Datenbanksysteme‘) of the open e-content platform www.geoinformation.net.

Data manipulation in SQL 06/04/2019

Motivation There are various reasons for manipulating a database system. The stored data is to be changed. In this lecture: insertion, deletion, and updating of datasets The data structure (the schema) is to be changed In this lecture: creation, dropping, and altering tables The performance is to be changed (tuning). Install an index, etc. Not in this lecture. The first two types of manipulation can be formulated using Standard-SQL. 06/04/2019

Insertion of Datasets SQL-command: INSERT given: A table containing information about students scenario: A new student has to be added to the database SQL command column names (optional) values to be inserted 06/04/2019

Set-based Insertion Datasets from other tables can be ‘imported‘ using a subquery. Task: All students with approved enrolment are to be inserted into the table “Studenten“. INSERT INTO Studenten SELECT Nr,Name,Ort FROM ImmatrApplications WHERE Status=“approved“ Important: Changes to the database are applied in 2 steps: create the set of candidates (temporary) make changes visible (all at the same time) Thus: no dependencies between the table to be changed and the subquery! 06/04/2019

Default Values Problem: What happens if we omit certain values in an INSERT comand? set default values when creating the table! 06/04/2019

Updating Datasets (1) SQL-command: UPDATE Scenario: The dataset of student number 5 is to be updated, because he has moved from Köln (Cologne) to Hannover. SQL command assignment constraint 06/04/2019

Updating Datasets (2) The WHERE clause is used to specify the set of tuples to be changed. This way multiple datasets can be changed simultaneously. scenario: Lecturer Meier (PersNr 2) is leaving the university. Lecturer Schmitz (PersNr 3) takes over his lectures. without where clause all datasets are changed multiple simultaneous assignments are possible: SET Name=“Weber“, Ort=“Berlin“, Strasse=“Hauptstr.“ 06/04/2019

Updating Datasets (3) 50 Example: The UPDATE operation can refer to old values. Example: Increase the examination score of student “Schneider“ (Nr=5) by 10%! UPDATE Klausurergebnisse SET Punkte = 1.1*Punkte WHERE Nr = 5; 50 06/04/2019

Deleting Datasets SQL-command: DELETE All tuples from a table T can be deleted using “DELETE FROM T“. Scenarios: Student number 1 is leaving the university. All students from Bonn are leaving the university. 06/04/2019

Schema Manipulation (1) SQL-commands: DROP TABLE, CREATE TABLE, ALTER TABLE Tables may be created any time with: CREATE TABLE Tables may be removed any time with: DROP TABLE …on the distinction of DROP TABLE T and DELETE FROM T: 06/04/2019

Schema Manipulation (2) The structure of tables can be altered any time. adding a column ALTER TABLE Vorlesungen ADD COLUMN Wochenstunden integer deleting a column DROP COLUMN Wochenstunden Integrity constraints (see lecture on “data integrity“) can also be added and removed at any time. 06/04/2019

References Jim Melton, Alan R. Simon, SQL 1999: Understanding Relational Language Components, Morgan Kaufmann Publishers, 2001 06/04/2019