sql interview questions for business analyst: SQL Interview Questions for Business Analysts

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    2023-05-01T10:40:53+00:00
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    sql interview questions for business analyst: SQL Interview Questions for Business Analysts

    Introduction

    SQL is a language used to query databases. A query retrieves and sometimes modifies data in a database. SQL combines data from multiple tables into one result set.

    What is SQL?

    SQL (structured query language) is a standard language for manipulating data in relational databases. It was developed by IBM in the 1970’s, and has been revised several times since then.

    SQL is a declarative language, not an imperative one. This means that you tell your database what you want it to do without telling it how to do it–you don’t have to specify how many times or how long each statement should take place or any other details about how your commands are executed by the system; instead, those decisions are left up to whatever programing interface (API) has been implemented by your database vendor and/or administrator(s).

    What is the purpose of using the SELECT statement?

    The SELECT statement is used to retrieve data from a database. It can be used in conjunction with other statements, such as UPDATE, INSERT, and DELETE. The SELECT statement has many variations that allow you to manipulate the data returned by your query.

    The most common use of the SELECT command is to retrieve all rows from one table or view at a time (SELECT * FROM table). This can be useful when you want to view all columns as well as their values within a single row:

    What are the two types of subqueries?

    A subquery is a query that is nested inside another query. The two types of subqueries are correlated and non-correlated.

    A correlated subquery returns data from the same table as its parent query, so it can only be used in the FROM clause of an outer SELECT statement. You can use a WHERE clause with a correlated subquery to filter the results before they’re returned by the outer query.

    A non-correlated subquery returns data from its own tables and columns, which makes it possible to use these results as part of an expression in an outer SELECT statement without needing to join them with other tables first (as would happen if you had used only one table).

    What is a derived table?

    A derived table is a table that is created from the results of a query. It’s not stored in the database, but it can be used to create complex queries.

    A derived table is created using the SELECT statement and looks like this:

    SELECT column_name1,column_name2 FROM source_table WHERE condition;

    Which SELECT statement has a WHERE clause that uses a NULL expression?

    The answer to this question is SELECT * FROM tbl WHERE col1 = NULL.

    This is because the WHERE clause in this statement uses a literal value (null) for comparison with the column, instead of an expression involving operators such as > or < .

    The other two options are incorrect because they do not use an equals sign (=), but rather IS NULL , which means that no comparison will take place at all!

    How can you write an ORDER BY clause for multiple columns in a SELECT statement?

    • You can use commas to separate the columns:

    SELECT FirstName, LastName FROM Employees ORDER BY FirstName, LastName;

    • You can use semicolons to separate the columns:

    SELECT FirstName, LastName FROM Employees ORDER BY 1;2;3;4;5;6 (where 1 is the first column, 2 is the second column and so on)

    • Spaces are also allowed in SQL queries:

    SELECT * FROM Employee WHERE EmployeeID IS NULL AND Salary > 100000 ORDER BY 1 / 2 / 3

    How can you include more than one expression in an ORDER BY clause?

    • Use commas to separate expressions
    • Use parentheses to group expressions
    • Use the keyword ASC or DESC to specify the sorting order

    What does it mean to use the TOP clause with an ORDER BY clause?

    The TOP clause is used to limit the number of rows returned in a SELECT statement. The TOP keyword can be used with the ORDER BY clause to order the result set, but it cannot be used with DISTINCT or GROUP BY.

    In this example, we want to return only 10 results from our database:

    Why would you use DISTINCT?

    You can use DISTINCT to eliminate duplicate rows. For example, if you want to know which customers have placed orders for the same product, you could use DISTINCT to return only one row per customer:

    SELECT DISTINCT c . FirstName , c . LastName FROM Customer AS c

    Can you use DISTINCT with GROUP BY, WHERE and HAVING clauses in a single statement?

    Yes, you can use DISTINCT with GROUP BY, WHERE and HAVING clauses in a single statement.

    DISTINCT can be used with the SELECT statement to remove duplicate values from the result set.

    It can also be used with ORDER BY clause to order rows based on their distinct values. For example: SELECT DISTINCT col1 FROM tbl_test ORDER BY col1 DESC;

    SQL combines data from multiple tables into a single result set.

    SQL is a programming language for managing data. It combines data from multiple tables into a single result set, which can then be manipulated using SQL statements. For example, let’s say you have two tables: one called “users” and another called “contacts.” If you want to see all the users who also have contacts, you could write an SQL query that joins these two tables together and returns their results as-is (a table).

    This feature makes SQL very powerful–you can combine information from different databases and create new views of it based on what’s needed at any given time or in support of your business objectives.

    Conclusion

    You’ve learned the basics of SQL, and you’re ready to take your knowledge to the next level. In this article, we covered some of the most important features of SQL–including SELECT statements, subqueries and derived tables–and how they can be used in business applications. If you want more information about SQL or other database languages like PL/SQL or Java Database Connectivity (JDBC), check out our other resources on this site!

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