/ Recent content on Michael Fuchs SQL Hugo -- gohugo.io en-us Fri, 01 Oct 2021 00:00:00 +0000 /2021/10/01/data-types-settings-in-oracle-data-modeler/ Fri, 01 Oct 2021 00:00:00 +0000 /2021/10/01/data-types-settings-in-oracle-data-modeler/ 1 Introduction 2 Overview of the most common Data Types 2.1 String Data Types 2.2 Numeric Data Types 2.3 Date and Time Data Types 3 Deep Dive: Numeric Data Types 3.1 DECIMAL 3.2 NUMMERIC 3.3 FLOAT 4 Conclusion 1 Introduction In my last post (Oracle SQL Developer Data Modeler) I showed, among other things, how to create tables with variables of different data types. /2021/09/01/oracle-sql-developer-data-modeler/ Wed, 01 Sep 2021 00:00:00 +0000 /2021/09/01/oracle-sql-developer-data-modeler/ 1 Introduction 2 Installations and Setup 2.1 Downlaod the Data Modeler 2.2 Downlaod Java SDK 2.3 Change Language 3 Oracle - Data Modeler 3.1 Creation of an Entity 3.2 Creation of an Attribute 3.2.1 NUMERIC 3.2.2 VARCHAR 3.3 A Glimpse on the Logical Writer 3.4 Assignment of a Primary Key 3.5 Setting a Table Relationship 3.6 Engineer to Relational Model 3.7 A Glimpse on the Relational Writer 3. /2021/08/01/how-to-backup-a-database/ Sun, 01 Aug 2021 00:00:00 +0000 /2021/08/01/how-to-backup-a-database/ 1 Introduction 2 Preparation 3 Backup a Database 3.1 via SSMS Object Explorer 3.2 via SQL Query 4 Restore a Database 4.1 via SSMS Object Explorer 4.2 via SQL Query 5 Conclusion 1 Introduction If you want to work on a private database, it is advisable to back it up at regular intervals. How to do this with the Microsoft SQL Server Management I want to show you in this post. /2021/05/16/normalization-of-databases/ Sun, 16 May 2021 00:00:00 +0000 /2021/05/16/normalization-of-databases/ 1 Introduction 2 Theoretical Background 2.1 What is Normalization in a Database? 2.2 Problems without Normalization 2.3 Rules for Data Normalization 3 Database Normalisation 3.1 First Normal Form (1st NF) 3.1.1 Same Data Type in a Column 3.1.2 There are only Single Valued Attributes 3.1.3 There is a Unique name for every Attribute/Column 3.1.4 Uniquely identify a Row 3.1.5 Digression: Primary Key vs. Foreign Key 3. /2021/05/13/types-of-sql-commands/ Thu, 13 May 2021 00:00:00 +0000 /2021/05/13/types-of-sql-commands/ 1 Introduction 2 Types of SQL Commands 2.1 Data Definition Language (DDL) 2.2 Data Query Language (DQL) 2.3 Data Manipulation Language (DML) 2.4 Data Control Language (DCL) 2.5 Transaction Control Language (TCL) 2.5.1 Preparation 2.5.2 Update a Table 2.5.3 TRANSACTIONS 2.5.3.1 COMMIT TRANSACTION 2.5.3.2 ROLLBACKS 2.5.3.3 SAVEPOINTS 3 Conclusion 1 Introduction After I have already written some posts about different SQL functions I would like to write a structure-bringing publication at this point again. /2021/05/10/local-and-global-temp-tables/ Mon, 10 May 2021 00:00:00 +0000 /2021/05/10/local-and-global-temp-tables/ 1 Introduction 2 Common SQL Tables 2.1 Creation of a Normal Table 2.2 Accessibility of the Table 3 Local Temporary Tables 3.1 Creation of a Local Temporary Table 3.2 Accessibility of the Local Temporary Table 3.2 Accessibility of the Tables via Another Database 4 Global Temporary Tables 4.1 Creation of a Global Temporary Table 4.2 Accessibility of the Global Temporary Table 4. /2021/05/08/update-a-table/ Sat, 08 May 2021 00:00:00 +0000 /2021/05/08/update-a-table/ 1 Introduction 2 Preparation 3 The SQL UPDATE Statement 3.1 UPDATE Command 3.2 UPDATE with WHERE 4 Difference between ALTER and UPDATE Command 5 Conclusion 1 Introduction Now that we know how to create new tables using SQL statements, I would like to show you how to modify them. 2 Preparation For the following examples, I set up a new database. /2021/05/06/generation-of-new-tables/ Thu, 06 May 2021 00:00:00 +0000 /2021/05/06/generation-of-new-tables/ 1 Introduction 2 Preparation 3 Join the tables 4 Generation of new Tables 4.1 via SELECT * INTO … FROM … 4.2 with certain selected Variables 4.3 from a generated View 5 A look at the Object Explorer 6 Conclusion 1 Introduction In my last post (Views) I showed how to save the output of a SELECT statement as a view and how to continue working with created views. /2021/05/03/views/ Mon, 03 May 2021 00:00:00 +0000 /2021/05/03/views/ 1 Introduction 2 Preparation 3 Join the tables 4 Views 4.1 Create VIEW 4.2 Update VIEW 4.3 Drop a View 4.4 Work with multiple Views 5 Conclusion 1 Introduction The SQL VIEW is a virtual table that does not physically exist. Rather, it is based on the result set of an SQL statement. The advantage of a view is that it can join data from several tables thus creating a new view of it. /2021/04/29/union/ Thu, 29 Apr 2021 00:00:00 +0000 /2021/04/29/union/ 1 Introduction 2 Preparation 3 The SQL UNION Operator 3.1 UNION 3.2 UNION ALL 3.3 UNION with WHERE 3.4 UNION with GROUP BY 4 Difference between JOIN and UNION 5 Conclusion 1 Introduction After the topic of joins, I now come to another very useful operator: Union With the UNION command you have the possibility to connect several select statements with each other. /2021/04/21/joins/ Wed, 21 Apr 2021 00:00:00 +0000 /2021/04/21/joins/ 1 Introduction 2 Preparation 3 Types of Joins 3.1 Inner Join 3.2 Left Join 3.3 Right Join 3.4 Outer Join 3.5 Left Excluding Join 3.6 Right Excluding Join 3.7 Outer Excluding Join 4 Multiple Joins 5 Join Tables from 2 different Databases 6 Conclusion 1 Introduction Source: C.L. Moffatt A topic which must not be missing in the course of SQL are Joins. In this article I will talk about the different types of joins and explain how they work and what differences they have to each other. /2021/04/12/window-functions/ Mon, 12 Apr 2021 00:00:00 +0000 /2021/04/12/window-functions/ 1 Introduction 2 Preparation 3 Window Functions 3.1 Simple Window Function 3.2 PARTITION BY & ORDER BY 3.3 Multiple Window Functions 3.3.1 Plausibility Check for Multiple Window Functions 3.4 Multiple PARTITION BY Statements 3.4.1 Plausibility Check for Multiple PARTITION BY Statements 3.5 PARTITION BY & ORDER BY Combined 3.5.1 with SUM() 3.5.2 with all kinds of aggregation functions 4 Advanced Window Functions 4. /2021/04/07/working-with-dates/ Wed, 07 Apr 2021 00:00:00 +0000 /2021/04/07/working-with-dates/ 1 Introduction 2 Preparation 3 Working with Dates 3.1 Extract Year, Month and Day 3.2 Extract Year, Month, Day, Hour, Minute, Second and iso week 3.3 ORDER and GROUP BY 3.4 Time Span 4 Conclusion 1 Introduction Following on from my post about string functions, I would like to take this opportunity to discuss how to use the Dates data type. 2 Preparation SET LANGUAGE ENGLISH CREATE DATABASE Dates_DB; USE Dates_DB; Important! /2021/04/03/string-functions/ Sat, 03 Apr 2021 00:00:00 +0000 /2021/04/03/string-functions/ 1 Introduction 2 Preparation 3 String Functions 3.1 Get the length of a character string 3.2 Get the length of numeric values 3.3 Get character index 3.4 Comparison of two strings 3.5 Receiving parts from a string 3.5.1 LEFT 3.5.2 RIGHT 3.5.3 SUBSTRING 3.6 Connecting character strings 3.6.1 With CONCAT 3.6.2 With CONCAT_WS 3.7 Separating character strings 3.8 Manipulating Strings 3. /2021/04/01/subqueries/ Thu, 01 Apr 2021 00:00:00 +0000 /2021/04/01/subqueries/ 1 Introduction 2 Preparation 2.1 Loading the data set flight 2.2 Creation of the flight_add_info dataset 2.3 Creation of the customers dataset 3 Subqueries 3.1 Subqueries in the WHERE statement 3.2 Nested Subqueries in the WHERE statement 3.3 Subqueries in the FROM statement 4 EXISTS Operator 5 ANY and ALL Operator 6 Conclusion 1 Introduction You can usually get pretty far with SQL using simple queries like we’ve seen so far. /2021/03/29/data-manipulation/ Mon, 29 Mar 2021 00:00:00 +0000 /2021/03/29/data-manipulation/ 1 Introduction 2 Preparation 3 Set Index 3.1 Create an Index via Primary Key 3.2 Create an Index via a new Column (recommended) 4 Replacing Values 4.1 Replace NULL Values (ISNULL) 4.2 Replace Values with NULL (NULLIF) 4.3 IF Else Statemtents in SQL (CASE) 4.3.1 Case with NULL Values 4.3.2 Case with other Values 4.3.3 Case with Lists 4.3.4 Case with a Range 4. /2021/03/26/data-aggregation/ Fri, 26 Mar 2021 00:00:00 +0000 /2021/03/26/data-aggregation/ 1 Introduction 2 Preparation 3 Data Aggregation 3.1 Count 3.2 Sum 3.3 Min, Max and Average 3.4 Group By & Order By 3.4.1 Simple Group By with AVG 3.4.2 Group and Order By with AVG 3.4.3 Group and Order By with ABS & STDEV 3.4.4 Group and Order By with MAX 3.4.5 Multiple Group and Order By 3.5 Having 3.6 Order By in a specific order 4 Conclusion 1 Introduction Now that we have got to know the best-known methods from the field of Data Wrangling, we come to the possibilities of Data Aggregation. /2021/03/23/data-wrangling/ Tue, 23 Mar 2021 00:00:00 +0000 /2021/03/23/data-wrangling/ 1 Introduction 2 Preparation 3 Get an Overview of the Data 3.1 Count Rows 3.2 Count Columns 3.3 Get Distinct Values 3.3.1 Digression: Difference between Unique vs. Distinct 3.3.2 Get distinct values 4 Data Wrangling 4.1 Select specific columns 4.2 Output columns in a specific order 4.2.1 Order ascending 4.2.2 Order descending 4.2.3 Multiple Orders 4.3 Conditional Statements (WHERE) 4. /2021/03/20/read-and-write-to-files/ Sat, 20 Mar 2021 00:00:00 +0000 /2021/03/20/read-and-write-to-files/ 1 Introduction 2 Reading csv-files 2.1 via SQL Query 2.2 via SSMS 3 Write to csv 4 Conclusion 1 Introduction Before we get into the interesting things like Data Wrangling, Aggregation and Manipulation, I would like to briefly explain the import and export of files in SSMS. For this post I created a TestCSV.csv and used the dataset flight from the statistics platform “Kaggle”. /2021/03/19/aliases/ Fri, 19 Mar 2021 00:00:00 +0000 /2021/03/19/aliases/ 1 Introduction 2 What is an Alias ? 3 Setting up the database and the required tables 4 Aliases 4.1 Alias for Columns 4.2 Alias for Tables 4.3 Alias for Joins 5 Conclusion 1 Introduction Today I would like to discuss a topic that is used in almost every SQL statement: Aliases 2 What is an Alias ? Aliases are “replacement names” for the columns and tables that can be used in an SQL statement. /2021/03/16/create-a-m-m-relationship/ Tue, 16 Mar 2021 00:00:00 +0000 /2021/03/16/create-a-m-m-relationship/ 1 Introduction 2 The assumed Situation 3 Setting up the database and the required tables 4 Connecting the two tables 4.1 Create an Associative Table 4.1.1 AUTO INCREMENT via SQL Server 4.1.2 AUTO INCREMENT via My SQL 4.1.3 AUTO INCREMENT via Access 4.2 Review of the created relationships 5 Filling the tables 6 Queries on the tables 7 Conclusion 1 Introduction As already announced in my post Create a 1:m Relationship, we now come to the last general type of relationship between two tables that I would like to deal with here: a n:m relationship /2021/03/13/create-a-1-m-relationship/ Sat, 13 Mar 2021 00:00:00 +0000 /2021/03/13/create-a-1-m-relationship/ 1 Introduction 2 The assumed Situation 3 Setting up the database and the required tables 4 Connecting the two tables 5 Filling the tables 6 Conclusion 1 Introduction In my last post I showed how to set up and use a 1:1 relationship between two tables. Now I want to show the same for a 1:m relationship. 2 The assumed Situation Let’s say we are asked to develop a database for a school. /2021/03/10/create-a-1-1-relationship/ Wed, 10 Mar 2021 00:00:00 +0000 /2021/03/10/create-a-1-1-relationship/ 1 Introduction 2 The assumed Situation 3 Setting up the database and the required tables 3.1 Primary Key 3.2 Foreign Key 4 Connecting the two tables 5 Filling the tables 6 Shorter method 7 Conclusion 1 Introduction After I showed in my last post how to create a SQL database and how to insert tables with values into it, let’s go one step further. /2021/03/07/create-a-database/ Sun, 07 Mar 2021 00:00:00 +0000 /2021/03/07/create-a-database/ 1 Introduction 2 Getting Started 3 Microsoft SQL Server Management Studio 3.1 Create a new Database 3.2 Create a new Table 3.2.1 A glimpse at the new Table 3.2.2 Inserting values into the Table 3.2 Create a Database for Data Manipulation 3.2.1 Delete specific Columns 3.2.2 Add new Columns 3.2.3 Delete the table contents 3.2.3.1 Delete specific rows 3.2.3.2 Delete the entire content 3. /2021/03/03/entity-relationship-diagram-erd/ Wed, 03 Mar 2021 00:00:00 +0000 /2021/03/03/entity-relationship-diagram-erd/ 1 Introduction 2 What is a Entity Relationship Diagram? 3 Main components of ERDs 3.1 Entity 3.2 Attributes 3.3 Relationships 4 Special circumstances 4.1 Strong Entity 4.2 Weak Entity 4.3 Associative entity 5 Cardinality 5.1 Chen-Notation 5.2 Modified Chen Notation (MC-Notation) 5.3 Min-Max-Notation 5.4 Martin-Notation (Crow’s foot notation) 6 Different styles of displaying ER diagrams 7 Best Practice for Developing Effective ER Diagrams 8 Conclusion 1 Introduction Before we start creating databases with SQL, we need to ask ourselves what the database should look like in the end. /2021/03/01/types-of-databases/ Mon, 01 Mar 2021 00:00:00 +0000 /2021/03/01/types-of-databases/ 1 Introduction 2 SQL vs. NoSQL 2.1 Data Structure 2.2 Ability to query Data 2.3 Scaling 3 Database Options 3.1 On-premise SQL Databases 3.2 SQL Databases on Cloud-Service Platforms 3.3 On-premise NoSQL Databases 3.4 NoSQL Databases on Cloud-Service Platforms 4 Conclusion 1 Introduction Herewith I start a new blog series. After covering all kinds of topics about Data Science on my R page and Python page, I now want to get into the topic of databases and SQL. /about/ Thu, 05 May 2016 21:48:51 -0700 /about/ Data Science enthusiastic ! Always hungry for more and deeper knowledge.. If you have any questions or comments, just text me: FuchsMichaelAndi1989@gmail.com