How much SQL is needed for Test Engineer?

Often wondered how much database knowledge is must for a Test Engineer?

Most of the case simple querying to database does the job. It is recommended to have some more than just simple 

Select * from tablename;

Basics concepts of when to use Group By clause.Also, aggregate functions like count, sum, NVL, etc.

Know how to use joins and difference between inner and outer (left and right) joins.

Some advance concepts like indexing like use of Primary and Foreign Key and Unique key.

Executing the User defined function and Stored Procedure.Difference between Store Procedure and Function.

 

If you are comfortable learn about query optimization. ACID properties of transactions

Often most of the time out of nervousness candidate mix up the concepts learned or are unable to demonstrate knowledge.

Once such example is unable to write query on paper during face to face interview.

Such situations can only be avoided by practice and practice writing queries on paper. One needs to create plan how to get the data and then how to present it.

Also, attempt to derive to same results using different query methods.

Like solving same problem using sub-queries and again using joins.

Sometimes, using sub-queries eliminates complex condition in the inner join.

To summarize,

 

• Practice SQL queries on online platforms.
• Use pen and paper first to come to solution.

Keep the open mind and don't over indulge in using only one way of query designing to get data from the database.