added select and joins examples

tasks/Wiederholung-01.12.2023.sql

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+USE tutorial;
+
+/* Cartesian product (every row combined with every other row) and filter out rows */
+SELECT
+    em.id AS 'Employee ID',
+    em.surname AS 'Surname',
+    em.forename AS 'forename',
+    at.id AS 'Title ID',
+    at.name AS 'Title'
+FROM
+    Employee AS em,
+    AcademicTitle AS at
+WHERE
+    em.surname LIKE 'Ma%'
+    AND at.id = em.academicTitleId;
+
+/* only select rows which have a matching (true) condition */
+SELECT *
+FROM Employee AS em
+INNER JOIN AcademicTitle AS at
+    ON em.academicTitleId = at.id
+WHERE
+    em.surname LIKE 'Ma%';
+
+SELECT
+    em.surname,
+    em.roomId AS 'Employee Room',
+    room.id AS 'Room ID',
+    room.name AS 'Room name'
+FROM Employee as em
+INNER JOIN Room as room ON em.roomId = room.id
+WHERE room.name LIKE 'a%';
+
+SELECT
+    count(*) AS Anzahl
+FROM Employee em
+LEFT JOIN PostalLocation post ON post.id = em.postalLocationId;

tasks/joins.sql

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+USE tutorial;
+
+SELECT positionId, forename, surname FROM Employee;
+
+/* select only one of duplicates */
+SELECT DISTINCT streetName FROM Employee;
+
+/* add further conditions with where */
+SELECT surname, EUR_GrossSalary FROM Employee
+                                WHERE academicTitleId = 1
+                                  AND (EUR_GrossSalary BETWEEN 40000 AND 50000)
+                                  AND EUR_GrossSalary != 46000;
+
+/* filter out non existing entries */
+SELECT * FROM  PostalLocation
+         WHERE cityDistrictName NOT LIKE ''
+            OR cityDistrictName IS NOT NULL;
+
+/* check if something is a member of a list */
+SELECT  * FROM Employee WHERE academicTitleId IN (0, 1);
+
+/* in with a sub query */
+SELECT  * FROM Employee WHERE academicTitleId IN (
+    SELECT academicTitleId FROM AcademicTitle WHERE academicTitleId > 1
+    );
+
+/* check string for pattern */
+/* %: zero or more characters */
+/* _: one character */
+SELECT surname FROM Employee WHERE surname LIKE 'A%';
+
+/* where with regex */
+SELECT surname FROM Employee WHERE REGEXP_LIKE(surname, '^[aB].*');
+
+/* selects employees with have academic title of 1 or (exclusive) surname starts with B */
+SELECT * FROM Employee WHERE academicTitleId = 1 XOR surname LIKE 'B';