SQL Tutorial: Introduction to SQL Server

Pubblicato il: 31 marzo 2020
sul canale di: DataCamp

1,991

Want to learn more? Take the full course at https://learn.datacamp.com/courses/in... your own pace. More than a video, you'll learn hands-on coding & quickly apply skills to your daily work.

---
Welcome to the course!

Most of the world's data live in databases, so learning how to access and extract insights from these data is an essential skill for any data scientist.

SQL, or S-Q-L, stands for Structured Query Language, and is the native language for working with databases.

SQL Server is a popular relational database system developed by Microsoft.

Transact-SQL, or T-SQL, is Microsoft's implementation of SQL, with additional functionality.

In this course, you will master the fundamentals of T-SQL and become prepared to work with SQL Server databases.

You'll do this by writing queries, or statements.

Let's get started!

Think of going to the supermarket - we have a store full of goods - that's our database.

We want to fill our cart with products, and those products are our query results.

Unlike the supermarket, we can't physically retrieve our data and manipulate it, so we write queries to make this happen.
The key term when retrieving data from tables is SELECT.

SELECT statements specify what we want to retrieve from a table.

The simplest query selects one column, from one table. In this query, we select the description column, from the table 'grid'. Note the semicolon which denotes the end of the query.

The other keyword you will always need is FROM - to specify the location of the source table.

Here are the results. By default, the query returns every row in the selected column.

You can select multiple columns, separating each column name with a comma.
However,you don't need a comma for the final column selected before 'FROM'.

Here are 2 similar queries, with different layouts.

The top query shows all the columns to be selected in one line.

The bottom query shows each selected column on a new line.

The results of both queries will be identical.
We will mainly use the bottom layout throughout the course.

Keeping keywords such as SELECT and FROM in uppercase, and table and column names in lower case, makes queries easier to read.

Instead of returning every row, we can use TOP() to limit the number of rows returned. Specify the number of rows to return between the brackets.

You can also specify a percentage of rows to return using TOP N PERCENT, where N is the percent of rows to return.

Using SELECT with TOP is a good way to get a quick view of the contents of a table.

Use SELECT DISTINCT to return a list of unique values from a column.
If you use SELECT DISTINCT with two or more columns, you'll return each unique combination of values.

Use SELECT, followed by the star, or asterisk key, to return all the rows and columns in a table.

This is fine for quick exploration of small tables, but not for very large tables or production code.

It's better to explicitly SELECT columns so that your queries produce reliable outputs.

You can rename, or ALIAS, a column to make your results more meaningful.

Simply select the column, followed by AS, and then your desired column name.

Note how demand_loss_mw is returned as lost_demand, while description is returned as cause_of_outage.

We've learned quite a lot! Let's start writing some queries!

#SQLTutorial #DataCamp #SQLServer

In questa pagina del sito puoi guardare il video online SQL Tutorial: Introduction to SQL Server della durata di ore minuti seconda in buona qualità , che l'utente ha caricato DataCamp 31 marzo 2020, condividi il link con amici e conoscenti, su youtube questo video è già stato visto 1,991 volte e gli è piaciuto 16 spettatori. Buona visione!

64,036

2.7K