From f52207eed34db79ed4d81945821f9a980ff05397 Mon Sep 17 00:00:00 2001
From: Klagarge <remi@heredero.ch>
Date: Thu, 29 Feb 2024 15:01:47 +0100
Subject: [PATCH] finish lab

---
 infotro/SDi/labs/database/README.md | 64 ++++++++++++++++++++++++++++-
 1 file changed, 63 insertions(+), 1 deletion(-)

diff --git a/infotro/SDi/labs/database/README.md b/infotro/SDi/labs/database/README.md
index 8f14d03..feb201f 100644
--- a/infotro/SDi/labs/database/README.md
+++ b/infotro/SDi/labs/database/README.md
@@ -300,4 +300,66 @@ WHERE `FunctionList`.`modelID` is NULL
 >
 
 
-# Test constraints
\ No newline at end of file
+# Test constraints
+
+#### 1) Try to insert a record in a table using an existing primary key.
+```sql
+INSERT INTO `Code`(`codeId`, `codeValue`)
+VALUES (1, 42)
+```
+> [!NOTE|label:Result]
+> #1062 - Duplicate entry '1' for key 'Code.PRIMARY'
+
+#### 2) Choose a table with at least a foreign key. Try to insert a record in that table, with the foreign key pointing to a non-existent record.
+```sql
+INSERT INTO `Model`(`modelId`, `manufacturerID`, `typeID`, `modelName`)
+VALUES (7, 1, 42, 'dummy test')
+```
+> [!NOTE|label:Result]
+> #1452 - Cannot add or update a child row: a foreign key constraint fails (`sdi04`.`Model`, CONSTRAINT `Model_ibfk_2` FOREIGN KEY (`typeID`) REFERENCES `Type` (`typeID`) ON DELETE RESTRICT ON UPDATE RESTRICT)
+
+#### 3) Try to delete the record with name “`HEVs`” in the table `Manufacturer`. Explain why this operation fails.
+```sql
+DELETE FROM `Manufacturer`
+WHERE `Manufacturer`.`manufacturerName` like 'HEVs'
+```
+> [!NOTE|label:Result]
+> #1451 - Cannot delete or update a parent row: a foreign key constraint fails (`sdi04`.`Model`, CONSTRAINT `Model_ibfk_1` FOREIGN KEY (`manufacturerID`) REFERENCES `Manufacturer` (`manufacturerID`) ON DELETE RESTRICT ON UPDATE RESTRICT)
+
+#### 4) Modify the foreign key definition in `Model` so that “`HEVs`” entry in `Manufacturer` can be deleted. The foreign key `manufacturerID` value in `Model` should be set to `NULL`. Test that it works as expected.
+```sql
+ALTER TABLE `Model` CHANGE `manufacturerID` `manufacturerID` INT NULL;
+
+ALTER TABLE `Model` DROP FOREIGN KEY `Model_ibfk_1`;
+
+ALTER TABLE `Model` ADD  CONSTRAINT `Model_ibfk_1`
+FOREIGN KEY (`manufacturerID`) REFERENCES `Manufacturer`(`manufacturerID`)
+ON DELETE SET NULL ON UPDATE RESTRICT;
+
+DELETE FROM `Manufacturer`
+WHERE `Manufacturer`.`manufacturerName` like 'HEVs'
+```
+> [!NOTE|label:Result]
+> 1 row deleted
+
+#### 5) We want now to delete all `Model` entries somehow related to a manufacturer when the latter is deleted from `Manufacturer`. To implement this feature, we should add a constraint `ON DELETE CASCADE` for the `manufacturerID` foreign key in `Model`. Try this and notice that this does not work. The reason is the following: you are not allowed to delete an entry in `Model` because a `FunctionList` refers to that entry. You could use `ON DELETE CASCADE` for all foreign keys, but deleting a single `Manufacturer` can trigger deletion of a good portion of the database!
+```sql
+ALTER TABLE `Model` DROP FOREIGN KEY `Model_ibfk_1`;
+
+ALTER TABLE `Model` ADD  CONSTRAINT `Model_ibfk_1`
+FOREIGN KEY (`manufacturerID`) REFERENCES `Manufacturer`(`manufacturerID`)
+ON DELETE CASCADE ON UPDATE CASCADE;
+
+DELETE FROM `Manufacturer`
+WHERE `Manufacturer`.`manufacturerName` like 'Sony'
+```
+> [!NOTE|label:Result]
+> #1451 - Cannot delete or update a parent row: a foreign key constraint fails (`sdi04`.`FunctionList`, CONSTRAINT `FunctionList_ibfk_3` FOREIGN KEY (`modelID`) REFERENCES `Model` (`modelID`) ON DELETE RESTRICT ON UPDATE RESTRICT)
+
+
+```sql
+DELETE FROM `Manufacturer`
+WHERE `Manufacturer`.`manufacturerName` like 'Onkyo'
+```
+> [!NOTE|label:Result]
+> 1 row deleted