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SQL Basics

SELECT, WHERE, INSERT, JOIN, GROUP BY. Write 5 SQL statements into a .sql file. Schema is in the task.

Duration: 30 minLevel: BeginnerExercises: 5

Your first SQL queries

SQL basics: your first queries

SQL (Structured Query Language) is the language for querying and changing databases. Data lives in tables (rows = records, columns = fields). Almost every application stores its data in an SQL database.

Key commands

SELECT: query data ("show me …").
WHERE: filters rows by a condition.
INSERT: adds a new record.
JOIN: connects two tables via a shared column.
GROUP BY + AVG(): groups rows and computes e.g. averages.

You write the SQL into .sql files under /home/student/sql/ (mkdir -p /home/student/sql). There are tables schueler (name, klasse, …) and noten (fach, note, …).

Your goal

You write five queries — from a simple selection to an analysis across multiple tables.

Exercises

1. Query all students
Concept: SELECT. SELECT * FROM table fetches all columns (*) of all rows of a table. Query all students.
```
mkdir -p /home/student/sql
echo "SELECT * FROM schueler;" > /home/student/sql/alle.sql
```
Check: alle.sql contains SELECT * FROM schueler.
2. Students of class 7a
Concept: WHERE. With WHERE you filter rows by a condition. Fetch only the students of class 7a.
```
echo "SELECT * FROM schueler WHERE klasse = '7a';" > /home/student/sql/klasse-7a.sql
```
Text values are in single quotes ('7a').

Check: klasse-7a.sql contains SELECT ... FROM schueler ... WHERE klasse = '7a'.
3. Insert a new student
Concept: INSERT. INSERT INTO adds a new record: first the columns, then the values. Add a new student.
```
echo "INSERT INTO schueler (name, klasse) VALUES ('Lisa', '7b');" > /home/student/sql/neu.sql
```
Check: neu.sql contains INSERT INTO schueler (... name ... klasse ...).
4. Grades with student name
Concept: JOIN. A JOIN connects two tables via a shared column (here the student ID), so you can show e.g. grades with the student's name.
```
echo "SELECT schueler.name, noten.fach, noten.note FROM schueler JOIN noten ON schueler.id = noten.schueler_id;" > /home/student/sql/noten-mit-namen.sql
```
Check: noten-mit-namen.sql contains SELECT ... FROM schueler ... JOIN noten.
5. Average grade per subject
Concept: aggregation (AVG + GROUP BY). Aggregate functions combine several rows into one value — AVG() computes the average. GROUP BY fach does it per subject.
```
echo "SELECT fach, AVG(note) FROM noten GROUP BY fach;" > /home/student/sql/schnitt.sql
```
Check: schnitt.sql contains SELECT ... AVG(note ... GROUP BY fach.

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Your first SQL queries

SQL basics: your first queries

Key commands

Your goal

Exercises

1. Query all students

2. Students of class 7a

3. Insert a new student

4. Grades with student name

5. Average grade per subject

Related courses

Now practice it yourself