Databases, specifically relational databases, are a powerful and efficient way to store and access massive amounts of data. You are all probably familiar with spreadsheet tools, like Excel or Google Sheets. In spreadsheets, you have a table with rows and columns. For example, let's say that each row is a patient and each column contains some data elements about the patient. Their name or date of birth. This format was really well when there is only one to insert each column for each patient. But this does not work so well when you have multiple events. Imagine that one of the columns is date of clinic visit, but Mister Smith has visited the clinic multiple times. Which date should go in the column? One option would be to make more columns and label them visit one, visit two, and so on. Another option would be to make a new row that duplicates all the information that is the same, or you can simply move to a relational database. Relational databases have multiple tables that in some way relate to one another. Let's take our previous example, and see how that data could be represented in a relational database. First, we could create a patient table that has the patient's name, and date of birth, plus a unique code that identifies them. This table then will only have one row for each patient. To record the clinic visits, we could create a table called encounters. This table has a row for each encounter. So a patient with multiple encounters will have multiple rows, one for each time they were seen. In this table, we will record which patient had the encounter, when that encounter occurred, and any other relevant details. We can also include a unique code for each encounter. Because I have the column Patient_ID in both tables, I can combine them based on that value. This is the relational part of relational databases. And this allows me to answer the question, who was seen in the clinic yesterday? I can simply match the visit record with the patient names. In addition to this structural difference between spreadsheets and databases, there is one other major difference you should know about. In spreadsheets, you can type anything into any field that you like. You can type a word, a date, or a number, even if it doesn't make sense as an answer for that column. This is not possible in databases. Each column in a database has a particular type, like a number, character, or time stamp. If your data does not follow the format in a particular column, it can not be entered into the database.