Essential SQL Commands For Data Science.
Tags: datascience, sql
Published: 2023-03-14 06:03:52


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Structured Query Language (SQL) is a programming language used to manage and manipulate data stored in relational database management systems (RDBMS). As a data scientist, mastering SQL is an essential skill to extract, transform and load data from databases. In this article, we'll cover some of the essential SQL commands for data science.

SELECT
The SELECT command is used to retrieve data from one or more tables. It is the most commonly used command in SQL. The basic syntax for SELECT command is:
             SELECT column1, column2, …
             FROM table_name;

For example, to retrieve all the data from a table called "customers," you would use the following command:

               SELECT *
               FROM customers;

WHERE
The WHERE command is used to filter data based on certain conditions. The basic syntax for WHERE command is:
               SELECT column1, column2, …
               FROM table_name
               WHERE condition;

For example, to retrieve all the data from a table called "customers" where the country is 'USA,' you would use the following command:

              SELECT *
              FROM customers
              WHERE country = 'USA';

GROUP BY
The GROUP BY command is used to group the result set based on one or more columns. The basic syntax for GROUP BY command is:
              SELECT column1, column2, …, 
              FROM table_name
              GROUP BY column1, column2, …;

For example, to retrieve the count of customers by country from a table called "customers," you would use the following command:

             SELECT country, COUNT(*)
             FROM customers
             GROUP BY country;

JOIN
The JOIN command is used to combine two or more tables based on a related column. The basic syntax for JOIN command is:
                SELECT column1, column2, …
                FROM table1
                JOIN table2
                ON table1.column = table2.column;

For example, to retrieve the customer information along with their order information from two tables called "customers" and "orders" where the common column is "customer_id," you would use the following command:

                SELECT *
                FROM customers
                JOIN orders
                ON customers.customer_id = orders.customer_id;

ORDER BY
The ORDER BY command is used to sort the result set in ascending or descending order based on one or more columns. The basic syntax for ORDER BY command is:
                 SELECT column1, column2, …
                 FROM table_name
                 ORDER BY column1 ASC|DESC, column2 ASC|DESC, …;

For example, to retrieve the customer information from a table called "customers" sorted by the customer's name in ascending order, you would use the following command:

                  SELECT *
                  FROM customers
                  ORDER BY customer_name ASC;

LIMIT
The LIMIT command is used to limit the number of rows returned by the SELECT command. The basic syntax for LIMIT command is:
                SELECT column1, column2, …
                FROM table_name
                LIMIT number_of_rows;

For example, to retrieve the top 10 customers from a table called "customers," you would use the following command:

                SELECT *
                FROM customers
             

### 
LIMIT 10;

In conclusion, SQL is a powerful tool for data manipulation and is a must-have skill for data scientists. Understanding and mastering these essential SQL commands will allow data scientists to effectively retrieve and analyze data from relational databases