56 lines
1.2 KiB
Markdown
56 lines
1.2 KiB
Markdown
![[sql_merged.pdf]]
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SQL Tabellen sind multimengen von tupeln
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Duplikate möglich!!!
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## SQL Data Definition Language DDL
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1. CREATE TABLE: zum Erstellen einer neuen Tabelle
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2. ALTER TABLE: zum Ändern einer bestehenden Tabelle
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3. DROP TABLE: zum Löschen einer Tabelle
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[[DDL Data Definition Language SQL]]
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## SQL Data Manipulation Language DML
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1. INSERT
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2. UPDATE
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3. DELETE
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[[DML Data Manipulation Language SQL]]
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| SQL | Argumente | Relationale Algebra |
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| ---------- | ------------------ | ------------------- |
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| **SELECT** | Liste von Namen | $\pi$ |
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| **FROM** | Liste von Tabellen | $\times$ |
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| **WHERE** | Bedingung | $\sigma$ |
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### SELECT
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```
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SELECT MatrNr, Name, Semester from Student
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```
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Spalte umbenennen
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`SELECT MatrNr AS InsassenNr from Student`
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Keine Duplikate
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`SELECT DISTINCT Semester AS Jahrgänge from Student`
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### WHERE
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```
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SELECT * from Student WHERE Semester = 2
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---
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SELECT * from Student s WHERE s.Semester = 2 AND s.Name='Byleth'
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```
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#### Anatomie einer WHERE Klausel
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Vergleichsoperatoren: <,>,=,<=,>=,<>
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BETWEEN
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LIKE
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IS NULL / IS NOT NULL
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AND, OR, NOT
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+,-,\*,/
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IN, NOT IN, $\theta$ ANY, $\theta$ ALL, EXISTS mit $\theta$ = Vergleichsoperator
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