Summary
After reading this chapter, you will be familiar with advanced concepts of PostgreSQL. We talked about views and materialized views, which are really significant. We also talked about cursors that help run a few rows at a time rather than full query at once. This helps avoid memory overrun when results contain a large number of rows. Another usage is to return a reference to a cursor that a function has created and allow the caller to read the rows. In addition to these, we discussed the aggregation concept by using the GROUP BY clause, which is really important for calculations. Another topic that we discussed in this chapter is subquery, which is a powerful feature of PostgreSQL. However, subqueries that contain an outer reference can be very inefficient. In many instances, these queries can be rewritten to remove the outer reference, which can improve performance. Other than that, the concept we covered is join, along with self, union, and outer join; these are really helpful when we need data from multiple tables. In the next chapter, we will discuss conversion between the data types and how to deal with arrays. Also we will talk about some complex data types, such as JSON and XML.