SQL

Question 1

What is the purpose of the group functions in SQL? Give some examples of group functions.

Answer 1

Group functions are necessary to get summary statistics of a data set. COUNT, MAX, MIN, AVG, SUM, and DISTINCT are all group functions.

Question 2

Tell me the difference between an inner join, left join/right join, and union.

Answer 2

“In a Venn diagram the inner join is when both tables have a match, a left join is when there is a match in the left table and the right table is null, a right join is the opposite of a left join, and a full join is all of the data combined.”

Question 3

What does UNION do? What is the difference between UNION and UNION ALL?

Answer 3

“UNION removes duplicate records (where all columns in the results are the same), UNION ALL does not.”

Question 4

What is the difference between SQL and MySQL or SQL Server?

Answer 4

SQL stands for Structured Query Language. It’s a standard language for accessing and manipulating databases. MySQL is a database management system, like SQL Server, Oracle, Informix, Postgres, etc.