SQL Tutorial: Tables: At the core of every database

now that you've had a first look at your database let's delve into one of the most important concepts behind databases tables you might have noticed that there's some redundancy in the university professors table let's have a look at the first three records for example as you can see this professor is repeated in the first three records also his University the ETH Lausanne is repeated a couple of times because he only works for this University however he seems to have affiliations with at least three different organizations so there's a certain redundancy in that table the reason for this is that the table actually contains entities of at least three different types let's have a look at these entity types actually the table stores professors highlighted in blue University's highlighted in green and the organization's highlighted in brown there's also this column called function which denotes the role the professor plays at a certain organization more on that later let's look at the current database once again the graphic used here is called an entity relationship diagram squares denote so-called entity types while circles connected to these denote attributes or columns so far we have only modeled one so called entity type University Professors however we discovered that this table actually holds many different entity types so this updated entity relationship model on the right side would be better suited it represents three entity types professors universities and organizations in their own tables with respective attributes this reduces redundancy as professors unlike now need to be stored only once note that for each professor the respective University is also denoted through the university short name attribute however one original attribute the function is still missing as you know this database contains affiliations of professors with third party organizations the attribute function gives some extra information to that affiliation for instance somebody might act as a chairman for a certain third party organization so the best idea at the moment is to store these affiliations in their own table it connects professors with their respective organizations where they have a certain function the first thing you need to do now is to create four empty tables for professors universities organizations and affiliations this is quite easy with sequel you'll use the create table command for that at the minimum this command requires a table name and one or more columns with the respective data types for example you could create a weather table with three a plane named columns after each column name you must specify the data type there are many different types and you will discover some in the remainder of this course for example you could specify a text column and numeric column and the column that the requires fixed length character strings with five characters each these data types will be explained in more detail in the next chapter for now you will first create the four tables and then migrate data from the original table to them let's