Sloan Digital Sky Survey
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SQL Tutorial
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 1. Introduction
 2. A Simple Query
 Practice
 3. Common Searches
 4. More Samples
 Practice
 5. Multiple Tables
 Practice
 6. Aggregate Fcns.
 7. Group By
 8. Order By
 Practice
 9. Views
 10. Functions
 Practice
 11. Conclusion
SQL Tutorial

Congratulations!

You've worked hard to get here, but you've done it - you've finished Level 1 of SkyServer's SQL tutorial. You now know enough to search SkyServer's massive database for just the data you need. Happy searching!

For more examples of SQL queries, see the Sample SQL Queries page. That page contains many queries that were written by SkyServer users (mostly scientists) to answer interesting science questions.

For more information about using SQL with SkyServer, including advice on how to make your queries run faster, see Using SQL with SkyServer.

Here are a few challenge questions that will give you more practice with SQL. With everything you now know, you should be able to write SQL queries to answer these questions.

Challenge 1. What percentage of galaxies have spectral redshifts measured? What percentage have photometric redshifts taken? What are the advantages of using photometric redshift? Try to compare photometric and spectral redshift; how accurate are photometric redshifts?

Challenge 2. What are the limits in ra and dec of stripes 42 and 43, two of the SDSS's diagonal stripes?

Challenge 3. Look at colors and spectra of stars, and find stars consistent with white dwarfs. Create a list of white dwarfs in the SDSS database.

Challenge 4. What are the largest galaxies in the SDSS, in terms of size?
HINT: Look at surface brightness and ellipticity.

Challenge 5. Find all objects with spectra classified as unknown.

Challenge 6. Find the broad absorption line (BAL) quasars in the SDSS database. At what redshifts are most BAL quasars found?

Challenge 7. Find variable stars in the SDSS (stars imaged more than once whose magnitudes changed by more than 0.1 between observations). How variable are the stars?

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Enter your SQL query in the text box. The query is limited to 10 minutes and 100,000 rows.