Sql interview questions

UNION merges the contents of two structurally-compatible tables into a single combined table. The difference between UNION and UNION ALL is that UNION will omit duplicate records whereas UNION ALL will include duplicate records. It is important to note that the performance of UNION ALL will typically be better than UNION, since UNION requires the server to do the additional work of removing any duplicates. So, in cases where is is certain that there will not be any duplicates, or where having duplicates is not a problem, use of UNION ALL would be recommended for performance reasons. ANSI-standard SQL specifies five types of JOIN clauses as follows: • INNER JOIN (a.k.a. “simple join”): Returns all rows for which there is at least one match in BOTH tables. This is the default type of join if no specific JOIN type is specified. • LEFT JOIN (or LEFT OUTER JOIN): Returns all rows from the left table, and the matched rows from the right table; i.e., the results will contain all records from the left table, even if the JOIN condition doesn’t find any matching records in the right table. This means that if the ON clause doesn’t match any records in the right table, the JOIN will still return a row in the result for that record in the left table, but with NULL in each column from the right table. • RIGHT JOIN (or RIGHT OUTER JOIN): Returns all rows from the right table, and the matched rows from the left table. This is the exact opposite of a LEFT JOIN; i.e., the results will conta...

The technical part of your employment process is quickly approaching. To get through it, you’re going to need to answer some tough SQL interview questions. There are going to be scenarios to explain, sample SQL queries to write, and commands to define, among other things. Well, you’ve come to the right place! Whether you’re looking to land a position as a database administrator, QA tester, software engineer, or business analyst, you’ll find the most important SQL interview questions to practice below. Arc is the radically different remote job search platform for developers where companies apply to you. We’ll feature you to great global startups and tech companies hiring remotely so you can ✔️ Rather than applying to job after job, have companies apply to you ✔️ Save time by batching your interviews in 14 days ✔️ High-quality opportunities only: both companies and developers are vetted ✔️ Receive personal coaching and advice to maximize your offers ✔️ Permanent remote jobs, freelancing roles, and contract openings available ✔️ Completely free of cost for developers! Arc makes it easier than ever for software developers and engineers to find great remote jobs. Fundamental SQL Interview Questions What are joins in SQL? A join is an operation that is used to combine data from multiple tables into a new table. Different types of joins specify how data between tables are matched into the new table. When you need to retrieve data from multiple tables in a single query, there’s a ...

Where can an SQL professional find a comprehensive guide to advanced SQL interview questions? The shortest answer is: here! We selected the 27 most important SQL questions and answered them for you. Preparing for an SQL interview is not easy, especially if your job requires the knowledge of advanced SQL. This article contains the 27 most commonly asked advanced SQL interview questions and provides detailed answers and resources for further reading. We’ll go through these four main concepts and a few more besides: • JOINs • GROUP BY, WHERE, and HAVING • CTEs (Common Table Expressions) and recursive queries • Window Functions The best way to refresh your advanced SQL knowledge is by taking our interactive Let’s attack these questions frontally, without further ado! 1. What Is a JOIN in SQL? JOIN is an SQL command that allows you to combine two or more tables. This is done via a common column (i.e. a column that has the same values in both tables), which allows using data from two or more tables at the same time. Joining tables in SQL is essential due to the nature of relational databases: data is atomized into tables, with each table holding only a part of the data available in the database. We’ll use two tables to showcase how this works. The first table is football_players. id first_name last_name national_team_id games_played 1 Gianfranco Zola 1 35 2 Virgil van Dijk 2 53 3 Marcus Rashford 3 51 4 Kylian Mbappé 5 66 5 Phil Foden 3 22 6 Frenkie de Jong 2 22 7 Mario Balotelli...