1. 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

2. Data manipulation in SQL
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3. 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.
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4. 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
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5. 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!
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6. Default Values Problem:
What happens if we omit certain values in an INSERT comand?
set default values when
creating the table!
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7. 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
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8. 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.“
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9. 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
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10. 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.
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11. 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:
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12. 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.
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13. References
Jim Melton, Alan R. Simon, SQL 1999: Understanding Relational Language Components, Morgan Kaufmann Publishers, 2001
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