![]() To create a new table, you use the CREATE TABLE statement. Tables allow you to store structured data like customers, products, employees, etc. PostgreSQL CREATE TABLE syntaxĪ relational database consists of multiple related tables. So, if you want to continue your theoretical preparation, feel free to jump into the next tutorial introducing you to the idea of declarative languages.Įager to hone your SQL skills? Enroll in our SQL course.Summary: in this tutorial, you will learn how to use the PostgreSQL CREATE TABLE statement to create new a new table. You just gained the knowledge of working with databases you need before you begin coding in SQL. A few related tables form a relational database. Each column represents a field that carries specific information about every record. To recap, remember that the data values in a row form a record in a data table. A single row of a table, being a single occurrence of that entity, we can also call it an entity instance. We can also refer to it as a database object. The table is a bigger data entity on its own. Therefore, the rows represent the horizontal in the table, the columns – its vertical entity. What are Entitiesįor those of you who are interested in slightly more technical definitions, remember the smallest unit that can contain a meaningful set of data is called an entity. One of the tables contains information about sales, the other, about customers, and the third about the items. And, importantly, each one bears a specific meaning and contains data characterizing it. Namely, these three tables – “Sales”, “Customers”, and “Items”– relate to the customer ID or the item code columns and form a relational database. Relational algebraallows us to use mathematical logic and create a relation between a few tables in a way that allows us to retrieve data efficiently. It is huge! Imagine what the table would look like if we had registered over 10 rows! My point is – there are too many columns, and it is hard to understand what type of information is contained in the larger table. Well, we could stuff this information into one table. Why You Should Avoid Using Only One Table Here, the connection between the “Sales” table and the “Items” table is not the customer ID, but the item code. It contains the item code product description its unit price ID the name of the company that has delivered it and the company headquarters' phone number. So, what would the logic of that structure be? Every time we have a customer with an ID number 1 in the “Sales” table, we can refer to the customer with ID number 1 in the “Customers” table and see his name, email, and the number of complaints filed. There are several fields, such as first and last names, gender, e-mail addresses, and the number of times customers have filed a complaint. The information about customers is stored in another example of a data table, called “Customers”. In this table, we know nothing about a customer besides their ID. This is important to mention because you will often see in the literature that database management relates to data stored in tabular form. When the data you have is organized into rows and columns, you are dealing with stored tabular data. It doesn’t matter if they are 10, 10 thousand, or 10 million or if they have a certain purchase number, date of purchase, customer ID, and item information. A field is a column in our example of a data table containing specific information about every record in the table. ![]() Fieldsīesides the rows, you can see the data is separated into four columns, or fields. The terms row and record can be used interchangeably. Therefore, the data values on the first-row form one record, while the selected data values regarding purchase number 2, form another record. ![]() We call each one a data value.Īll four data values make up one record. Data ValuesĮach of the four elements has a specific meaning. Purchase number 1 was registered on the 3 rd of September 2016, and it refers to Customer number 1 buying item A_1. The table you see in the picture below contains the customer sales data of a furniture store.Īnd, this is how we should read this information. This means by focusing on a single topic we will never get the full story. One thing you’ll notice when studying programming languages is that the concepts you encounter are interrelated. Introduction to Databases and an Example of a Data Table When you become a successful SQL programmer, working with multiple data tables will be a walk in the park. ![]()
0 Comments
Leave a Reply. |