Chapter/02 (#36)

* Finish chapter 2

* Fix Dockerfile

* Add introduction

Author: rainbowdashlabs

Dockerfile

@@ -0,0 +1,15 @@
+FROM python:3.10
+
+RUN pip install mkdocs-material && pip install mkdocs-git-revision-date-localized-plugin
+
+EXPOSE 8000
+
+WORKDIR "/docs"
+
+COPY mkdocs.yml /docs/mkdocs.yml
+
+COPY docs/ /docs/docs
+
+COPY .git/ /docs/.git/
+
+ENTRYPOINT ["mkdocs", "serve", "-a", "0.0.0.0:8000"]

docker-compose.yml

@@ -0,0 +1,10 @@
+version: "3.8"
+
+services:
+  docs:
+    volumes:
+      - "./docs/:/docs/"
+    build:
+      dockerfile: Dockerfile
+    ports:
+      - "80:8000"

docs/01/index.md docs/01/.index.md

@@ -0,0 +1,45 @@
+CREATE TABLE player
+(
+    id          INTEGER,
+    player_name TEXT,
+    last_online TIMESTAMP
+);
+
+CREATE TABLE friend_graph
+(
+    player_1 INTEGER,
+    player_2 INTEGER
+);
+
+INSERT INTO player(id, player_name, last_online)
+VALUES (1, 'Mike', '2022-05-11 00:00'::TIMESTAMP),
+       (2, 'Sarah', '2022-04-04 00:00'::TIMESTAMP),
+       (3, 'john', '2022-04-08 00:00'::TIMESTAMP),
+       (4, 'Lilly', '2022-04-01 00:00'::TIMESTAMP),
+       (5, 'Matthias', '2022-03-06 00:00'::TIMESTAMP),
+       (6, 'Lenny', '2022-03-08 00:00'::TIMESTAMP),
+       (7, 'Summer', '2022-05-22 00:00'::TIMESTAMP),
+       (8, 'Marry', '2022-06-04 00:00'::TIMESTAMP),
+       (9, 'Milana', '2022-02-12 00:00'::TIMESTAMP),
+       (10, 'Lexi', '2022-02-22 00:00'::TIMESTAMP);
+
+INSERT INTO friend_graph(player_1, player_2)
+VALUES (1, 2),
+       (2, 3),
+       (4, 3),
+       (5, 3),
+       (7, 2),
+       (6, 1),
+       (6, 2),
+       (1, 10),
+       (4, 10);
+
+CREATE TABLE money AS (
+    SELECT id, 1000.0 AS money
+    FROM player
+);
+
+UPDATE money
+SET money = money - 600
+WHERE id = 10
+  AND money >= 600

docs/02/index.md docs/02/.index.md

@@ -1 +1,61 @@
 # Delete
+
+After inserting all our data we only miss one basic functionality. Sometimes updating or inserting data is not
+enough. We also need to delete data.
+
+For this we use the `DELETE` keyword. The `DELETE` keyword is pretty similar to the [`SELECT` statement](select.md) we
+already know.
+We need to define `FROM` which table we want to delete and `WHERE` we want to delete those rows
+
+With this in mind we can probably assume that the general `DELETE` statement would look like this:
+
+```sql
+DELETE
+FROM table_name
+WHERE column_1 = value_1; 
+```
+
+Lets try to write a statement which would delete the user with id 10 from our users table:
+
+
+
+<details>
+<summary>Solution</summary>
+
+```sql
+DELETE
+FROM player
+WHERE id = 10;
+```
+
+</details>
+
+Now we just have one more problem... Out friend graph and money table still contain references to the player with
+id 10. To change this we need to delete those entries from these two tables as well.
+
+Write two statements.
+
+1. Delete all entries from friend_graph **where** the player 1 **or** player 2 has the id 10. (Do it in one statement.)
+2. Delete the entry of player 10 from the `money` table (If you haven't created the money table, you can simply
+   ignore it.)
+
+<details>
+<summary>Solution</summary>
+
+   ```sql
+DELETE
+FROM friend_graph
+WHERE player_1 = 10
+   OR player_2 = 10;
+
+DELETE
+FROM money
+WHERE id = 10;
+```
+
+</details>
+   
+Of course there is a better and more save solution to avoid "dead" entries in other tables. We will learn this in 
+another chapter.
+
+Now that we know the statements for `SELECT`, `INSERT`, `UPDATE` and `DELETE` we are ready for the next chapter.

docs/02/.scripts/postgres.sql

@@ -2,7 +2,7 @@
 
 Now that we have created our tables we want to add data to them.
 
-Lets start with our players
+Let's start with our players
 
 | id  | player\_name | last\_online     |
 |:----|:-------------|:-----------------|
@@ -43,7 +43,10 @@ use:
 - MariaDB/MySQL: `timestamp('2022-05-11 00:00')`\
   We use the timestamp function to parse our string
 - SqLite: `CAST(STRFTIME('%s', '2022-05-11 00:00') AS INTEGER)`\
-  We save timestamps as epoch seconds since sqlite doesnt really has a timestamp type
+  We save timestamps as epoch seconds since sqlite doesn't really has a timestamp type
+
+Now try to recreate the table from above with the previously mentioned methods and statements. Usually the time an 
+be ommited when it is set to 00:00.
 
 <details>
 <summary>Solution</summary>
@@ -94,7 +97,7 @@ VALUES (1, 'Mike', CAST(STRFTIME('%s', '2022-05-11 00:00') AS INTEGER)),
 
 </details>
 
-Lets to the same with the friend_graph
+Lets to the same with the friend_graph. Try to insert following values into the `friend_graph` table.
 
 | player\_1 | player\_2 |
 |:----------|:----------|
@@ -130,7 +133,7 @@ VALUES (1, 2),
 
 You can also use an alternative syntax to directly create a table with content.
 
-Lets say we want to create a table with money of the players. The table should contain the id and a fixed amount of 
+Let's say we want to create a table with money of the players. The table should contain the id and a fixed amount of 
 money for each player for now.
 
 ```sql

docs/02/delete.md

@@ -0,0 +1,15 @@
+# Chapter 2
+
+Welcome to chapter two. Now we have set up the database of our choice and also installed a tool to access our 
+databases. Of course, we could start now directly with writing cool SQL queries, but first we need to talk about 
+some very important stuff.
+
+We will start with learning about operators. Especially about operators to transform and compare data. Because those 
+operators heavily depend on the datatypes we use we will directly head over to them and take a look at the different 
+types our databases offer to us.
+
+Before we can now finally start with creating our first database and creating our tables we will need to define some 
+important thing, that is naming. A clear structure in your database will make your life a lot easier and helps 
+others to understand what you are doing.
+
+After this we will take a first look on how to create tables and insert, update, select and delete data in these tables.

docs/02/insert.md

@@ -55,7 +55,7 @@ CREATE TABLE table_name
 (
     col_name TYPE,
     col_name TYPE
-)
+);
 ```
 <!-- @formatter:on --> 
 
@@ -76,7 +76,7 @@ CREATE TABLE friend_graph
 (
     player_1 INTEGER,
     player_2 INTEGER
-)
+);
 ```
 
 </details>
@@ -91,7 +91,7 @@ CREATE TABLE IF NOT EXISTS table_name
 (
     col_name TYPE,
     col_name TYPE
-)
+);
 ```
 <!-- @formatter:on --> 
 

docs/02/introduction.md

@@ -20,10 +20,10 @@ Remember our already pretty known table of players.
 | 9   | Milana       | 2022-02-12 00:00:00.000000 |
 | 10  | Lexi         | 2022-02-22 00:00:00.000000 |
 
-We are currently saving the last time the player has logged in in the `last_online` column.
+We are currently saving the last time the player was online in the `last_online` column.
 
 When Lexy is online again we might need to update the `last_online` value for her again. We have now two options. The
-first one is deleting the entry and inserting a new one. This is very dirty and also not a good practice. Thats why we
+first one is deleting the entry and inserting a new one. This is very dirty and also not a good practice. That's why we
 use the `UPDATE` statement and define in the `WHERE` clause where we want to update and what we want to update.
 
 The general syntax is:
@@ -62,7 +62,6 @@ WHERE id = 10;
 
 <details>
 <summary>MariaDB/MySQL</summary>
-****
 
 ```sql
 UPDATE player

docs/02/tables.md

@@ -7,10 +7,10 @@ Chapter 3 Advanced Data
   - Default values
   - Sorted indices
   - Conditional indices
+- Auto increment
 - Upsert/Replace
 - Aggregation
   - Grouping
-- Auto increment
 - Foreign keys
 - Basic normalization
 - Joins

docs/02/update.md

@@ -29,6 +29,7 @@ nav:
     - 'Insert': 02/insert.md
     - 'Select': 02/select.md
     - 'Update': 02/update.md
+    - 'Delete': 02/delete.md
 theme:
   features:
     - navigation.instant