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DBA Job interview question thoughts


DBA Job interview question thoughts

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peter_parker
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Just out of curiosity how big a whiff would you consider not knowing the difference between a clustered and non-clustered index in SQL Sever?

We're hiring for an ETL "BI" guy/gal --- light DBA duties (like backups, monitoring) -- okay maybe not so light, but it would be nice.

I understand an ETL guru not necessarily need to be an expert in SQL server. That said ... uh ... turning indexes on and off during ETL may be important. "Reading" and tuning queries fast enough to be imported into OLAP cubes or wherever is important.

In your opinion, --- the difference between a clustered and non-clustered index in SQL Sever (I would have accepted that a clustered index is a physical ordering of the database).

If an interview candidate didn't know that, would you consider that junior level? Still potentially mid-level? Obviously they are not expert level with that response.

Curious if I'm making too much out of it.
DinoRS
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well how important turning indexes on / off highly depends on your architecture, if you process data in your DWH and Reporting is done somewhere else, you usually don't have many indexes you'd want to keep around anyways. But you should definitely know how to work with indexes because tuning will require knowing them rather well so I'd say junior level tops.
Grant Fritchey
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Funny enough, that's one of my phone screen questions. I'd say anyone that has to do more than consume data from SQL Server really has to know this. It's one thing if they're just moving data around. However, they're not simply going to disable/enable indexes, there's a good chance that they'll occasionally need to drop & recreate them. Not knowing what a clustered index is and the implications it has on non-clustered indexes is a sign of a junior person. However, that's my opinion, not hard fact.

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Michael L John
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peter_parker - Tuesday, March 12, 2019 3:50 PM
Just out of curiosity how big a whiff would you consider not knowing the difference between a clustered and non-clustered index in SQL Sever?

We're hiring for an ETL "BI" guy/gal --- light DBA duties (like backups, monitoring) -- okay maybe not so light, but it would be nice.

I understand an ETL guru not necessarily need to be an expert in SQL server. That said ... uh ... turning indexes on and off during ETL may be important. "Reading" and tuning queries fast enough to be imported into OLAP cubes or wherever is important.

In your opinion, --- the difference between a clustered and non-clustered index in SQL Sever (I would have accepted that a clustered index is a physical ordering of the database).

If an interview candidate didn't know that, would you consider that junior level? Still potentially mid-level? Obviously they are not expert level with that response.

Curious if I'm making too much out of it.

It depends.
If it was any candidate that was interviewing for any kind of DBA position, then that would be a show-stopper.
If it was a developer position, that would be a show-stopper if they were applying for anything higher than an entry level position. That being said, I'm betting that I could ask that question of the developers here and I might get 2 or 3 right answers!
A BI position is probably the same a developer, if they have done this kind of work, and have no real idea of the meaning of a clustered or non-clustered index, then they probably have not done anything too terribly difficult.


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Jeff Moden
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peter_parker - Tuesday, March 12, 2019 3:50 PM
Just out of curiosity how big a whiff would you consider not knowing the difference between a clustered and non-clustered index in SQL Sever?

We're hiring for an ETL "BI" guy/gal --- light DBA duties (like backups, monitoring) -- okay maybe not so light, but it would be nice.

I understand an ETL guru not necessarily need to be an expert in SQL server. That said ... uh ... turning indexes on and off during ETL may be important. "Reading" and tuning queries fast enough to be imported into OLAP cubes or wherever is important.

In your opinion, --- the difference between a clustered and non-clustered index in SQL Sever (I would have accepted that a clustered index is a physical ordering of the database).

If an interview candidate didn't know that, would you consider that junior level? Still potentially mid-level? Obviously they are not expert level with that response.

Curious if I'm making too much out of it.


I'm sure that there are many folks out there that will disagree with me but for people doing ETL (ELT, LET, or whatever you want to call it anymore), I personally consider an in depth understanding of indexes and indexing (along with "Minimal Logging" and what happens when you "turn an index on" (which isn't actually that simple) to be a critical skill. People that don't know those things don't even qualify as a "junior" in the area of ETL, IMHO.

--Jeff Moden

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When you put the right degree of spin on it, the number 318 is also a glyph that describes the nature of a DBAs job. Wink

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jonathan.crawford
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Jeff Moden - Thursday, March 14, 2019 10:18 PM


I'm sure that there are many folks out there that will disagree with me but for people doing ETL (ELT, LET, or whatever you want to call it anymore) [...]

GIGO? BigGrin


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Jeff Moden
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jonathan.crawford - Friday, March 15, 2019 7:40 AM
Jeff Moden - Thursday, March 14, 2019 10:18 PM


I'm sure that there are many folks out there that will disagree with me but for people doing ETL (ELT, LET, or whatever you want to call it anymore) [...]

GIGO? BigGrin


Perfect! BigGrin Same number of characters as "Crap". BigGrinBigGrinBigGrin

--Jeff Moden

RBAR is pronounced ree-bar and is a Modenism for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
If you think its expensive to hire a professional to do the job, wait until you hire an amateur. -- Red Adair

When you put the right degree of spin on it, the number 318 is also a glyph that describes the nature of a DBAs job. Wink

Helpful Links:
How to post code problems
How to post performance problems
Forum FAQs
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