Merge pull request #1436 from vegetabill/bill-pr-1396

Revise intro to relational databses

Author: vegetabill

databases/relational-databases.md

@@ -52,7 +52,6 @@ To understand, query, and insert information into a relational database, a techn
 
 - [Khan Academy's introductory SQL, videos](https://www.khanacademy.org/computing/computer-programming/sql/sql-basics/v/welcome-to-sql)
 - [four basic SQL operators](https://blog.sqlauthority.com/2008/05/13/sql-server-four-basic-sql-statements-sql-operations/)
-- [streaming(cassandra)](https://dzone.com/articles/cassandra-sink-for-spark-structured-streaming)
 
 #### Tools
 
@@ -61,28 +60,32 @@ To understand, query, and insert information into a relational database, a techn
 ### Lesson
 
 - [Slides](https://drive.google.com/open?id=1xK7_t_yJcu4RcBkj0Gv-t5uyBCNr0g4cHKqAJSxNwY0) | [Video Walkthrough of Slides](https://drive.google.com/file/d/1V0bk3fH_8PsRE3Vz4J3qe3TTiqBClT6y/view)
-
 - Look through the rest of the links in the Materials Section. [SQL Fiddle](http://sqlfiddle.com) is the tool where you can implement your sql knowledge. Practically implement creating a database schema and perform operations on it using the tool.
 
-#### Relational Database Basics
+### Relational Database Basics
 
 - The specific problems a database solves
 
-  - Persistence of information
+  - Storage of information
   - Centralized information
   - Search stored information
-  - Form relationships between sets of information
+  - Form relationships between tables containing information
+
+- [Common column data types](https://www.postgresql.org/docs/8.4/datatype.html#DATATYPE-TABLE)
+
+  - `varchar` (Just like **string** available in different programming languages like JS)
+  - `integer` (For holding Numeric Values)
+  - `boolean` (For storing true or false)
+  - `date` (stores the dates only)
+
+#### Primary key
+
+Every table must have a unique primary key, which is ofen a single integer column that increments automatically like a counter, but primary keys can be other types as well.
 
-- Few basic column types
-  - `varchar`
-  - `text`
-  - `integer`
-  - `primary key`, `auto increment`
-    - exact type varies depending on database type
 - The [four basic SQL operators](https://blog.sqlauthority.com/2008/05/13/sql-server-four-basic-sql-statements-sql-operations/) and their use
 
   - `SELECT`
-    - The SELECT statement is used to select data from a database.
+    - The SELECT statement is used to read rows from a database table.
     - selecting specific columns: \*, specific columns, AS column aliasing. Below are the syntax for the same.
       ```sql
       SELECT * FROM table_name;
@@ -135,19 +138,7 @@ To understand, query, and insert information into a relational database, a techn
       ```sql
       DELETE FROM table_name WHERE condition;
       ```
-    -
-    _The above examples are from [w3schools.](https://www.w3schools.com/sql/sql_select.asp)_
-
-- Other types of non-relational, non-sql databases that will be encountered
-
-  - key-value [(redis)](https://www.shellhacks.com/en/redis-set-get-key-value-redis-cli/)
-    - Redis is a key-value database (also known as a key-value store) that uses a simple key/value method to store data.
-      Strings are the simplest data type in Redis and are simple key/value entries.
-  - graph [(Neo4j)](https://github.com/JNOSQL/artemis-demo/tree/master/artemis-demo-java-se/graph-neo4j)
-    - Neo4j is a graph database management system developed by Neo4j, Inc. Described by its developers as an ACID-compliant transactional database with native graph storage and processing.
-  - document [(mongo)](https://docs.mongodb.com/getting-started/cpp/documents/)
-    - MongoDB is a document database: each record in a MongoDB collection is document. Documents are a structure composed of file and value pairs, similar to JSON objects or other mapping data types.
-  - [streaming(cassandra)](https://dzone.com/articles/cassandra-sink-for-spark-structured-streaming): Give the read to this article so that you can get idea about cassandra which is another non-sql database. You can even try out the code given in the article later to get complete understanding.
+      _The above examples are from [w3schools.](https://www.w3schools.com/sql/sql_select.asp)_
 
 ### Guided Practice
 
@@ -162,7 +153,7 @@ To understand, query, and insert information into a relational database, a techn
 
 ### Independent Practice
 
-**(IMP: While working on the following activities you can refer back to the prerequisites at any point of time for better understanding.)**
+**(IMPORTANT: While working on the following activities you can refer back to the prerequisites at any point of time for better understanding.)**
 
 **Activity #1**
 
@@ -203,6 +194,23 @@ Solve the quizzes mentioned below
 - How does SELECT command work?
 - How do you model data for relational databases?
 
+### Common Mistakes & Misconceptions
+
+- The term "database" can mean a collection of tables, a running database application like Postgres, or a physical/virtual machine running the application . You have to consider the context for better understanding.
+
+### Resources for Non-Relational Databases (OPTIONAL)
+
+Different types of [non-relational databases](https://medium.com/@mark.rethana/introduction-to-nosql-databases-c5b43f3ca1cc) (non-sql databases):
+
+- key-value [(redis)](https://www.shellhacks.com/en/redis-set-get-key-value-redis-cli/)
+  - Redis is a key-value database (also known as a key-value store) that uses a simple key/value method to store data.
+    Strings are the simplest data type in Redis and are simple key/value entries.
+- graph [(Neo4j)](https://github.com/JNOSQL/artemis-demo/tree/master/artemis-demo-java-se/graph-neo4j)
+  - Neo4j is a graph database management system developed by Neo4j, Inc. Described by its developers as an ACID-compliant transactional database with native graph storage and processing.
+- document [(mongo)](https://docs.mongodb.com/getting-started/cpp/documents/)
+  - MongoDB is a document database: each record in a MongoDB collection is document. Documents are a structure composed of file and value pairs, similar to JSON objects or other mapping data types.
+- [streaming(cassandra)](https://dzone.com/articles/cassandra-sink-for-spark-structured-streaming): Give the read to this article so that you can get idea about cassandra which is another non-sql database. You can even try out the code given in the article later to get complete understanding.
+
 ### Supplemental Resources
 
 - [Medium: Omar El Gabry's Tutorials on Databases, Modeling, Design Process, & Normalization](https://medium.com/omarelgabrys-blog/database-introduction-part-1-4844fada1fb0)