Important SQL Commands for Data Analyst
As a data analyst I have been asked in several interviews about the usage of different commands in SQL and from that I understand how important it is to get confidence on your SQL skills.Working with SQL, there are several important commands that you should be familiar with and in that case “must know” commands I have mentioned below:
- SELECT: This command is used to retrieve data from one or more tables in a database. It is often the first command used when querying a database.
- WHERE: This command is used to filter data based on specific criteria. It allows you to narrow down the results returned by a SELECT statement.
- GROUP BY: This command is used to group data based on one or more columns. It is often used in combination with an aggregate function such as SUM, COUNT, or AVG.
- ORDER BY: This command is used to sort the results of a SELECT statement in ascending or descending order based on one or more columns.
- JOIN: This command is used to combine data from two or more tables based on a common column. There are several types of joins, including INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN.
- DISTINCT: This command is used to retrieve only unique values from a column in a table. It is often used to remove duplicate rows from a query result.
- HAVING: This command is used to filter data based on aggregated values, such as the result of a GROUP BY statement.
- INSERT: This command is used to insert new rows into a table.
- UPDATE: This command is used to update existing rows in a table.
- DELETE: This command is used to delete rows from a table.
Before going to any interview revise the above mentioned commands along with their applications on database. Honestly I have been asked “Joins” alot in the interviews and how 4 joins will give different output. So now you know how to prepare.
If you are experienced professional with more than 2 years than below commands are must do for you, In addition to the basic SQL commands, there are several advanced SQL commands that can be useful for data analysts. check below-
- UNION: This command is used to combine the results of two or more SELECT statements into a single result set. It is often used when you need to combine data from two tables with similar structures.
- EXCEPT/INTERSECT: These commands are used to retrieve the difference or intersection between the results of two SELECT statements. EXCEPT returns the rows that are in the first result set but not in the second, while INTERSECT returns only the rows that are in both result sets.
- CASE: This command is used to create conditional expressions within a SELECT statement. It can be used to transform data or perform calculations based on certain conditions.
- WINDOW FUNCTIONS: These functions are used to perform calculations over a “window” of rows in a result set, based on a specific order. Examples of window functions include ROW_NUMBER, RANK, and LAG/LEAD.
- CROSS APPLY/OUTER APPLY: These commands are used to apply a table-valued function to each row of a result set. CROSS APPLY returns only the rows that match the function, while OUTER APPLY returns all rows, with NULL values for any rows that don’t match.
- PIVOT/UNPIVOT: These commands are used to transform a result set from a “long” format (where multiple columns represent a single variable) to a “wide” format (where each variable has its own column). PIVOT aggregates data based on a pivot column, while UNPIVOT “un-aggregates” the data.
- WITH/CTE: These commands are used to create a temporary table or “common table expression” (CTE) that can be used within a single query. CTEs can make complex queries easier to read and understand.
These advanced SQL commands can help data analysts to perform more complex data transformations and analysis tasks. So that was it, Hope you will get advantage from this article and you may apply it accordingly in your SQL preparation.
~If you still have any further questions, feel free to connect with me on Linkedin- https://www.linkedin.com/in/gauri-guglani-a87b731a6/
