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Was ist ein Join? > Inner Joins

Inner Joins

Um die obige Abfrage so zu modifizieren, dass nur mehr 18 Zeilen in die Ergebnismenge gelangen (eine pro Mitarbeiter), müssen Sie beschreiben, wie die beiden Tabellen zusammenhängen. Weiter oben habe ich gezeigt, dass die employee.dept_id-Spalte als Verbindung zwischen diesen beiden Tabellen fungiert. Diese Information muss also der on-Subklausel der from-Klausel hinzugefügt werden:

mysql> SELECT e.fname, e.lname, d.name
    -> FROM employee e JOIN department d
    ->   ON e.dept_id = d.dept_id;
+----------+-----------+----------------+
| fname    | lname     | name           |
+----------+-----------+----------------+
| Michael  | Smith     | Administration |
| Susan    | Barker    | Administration |
| Robert   | Tyler     | Administration |
| Susan    | Hawthorne | Operations     |
| John     | Gooding   | Loans          |
| Helen    | Fleming   | Operations     |
| Chris    | Tucker    | Operations     |
| Sarah    | Parker    | Operations     |
| Jane     | Grossman  | Operations     |
| Paula    | Roberts   | Operations     |
| Thomas   | Ziegler   | Operations     |
| Samantha | Jameson   | Operations     |
| John     | Blake     | Operations     |
| Cindy    | Mason     | Operations     |
| Frank    | Portman   | Operation....

  

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