Summary

In this chapter, you examined subqueries and saw how to combine data from multiple queries into a single result set. To be specific, you've looked at the following:

• Formulating simple subqueries

• Using subqueries that return multiple values

• Understanding the difference between correlated and non-correlated subqueries

• Using the UNION keyword

• Using ALL with UNION to retain duplicate rows

• Extracting matching/nonmatching data from queries with INTERSECT and EXCEPT/MINUS

This chapter has been the first in which you've combined data from several tables together. In the next chapter, you'll look at other ways of doing this that have their own advantages.