Implement JOIN in Postgres

Question

Can someone explain or point me to a resource that explains how a relational database (like Postgres or MySQL, I use Postgres) implements joins?

For example, I can roughly tell you that indexes can be made from tree B, where nodes are conditions that may be present in a sentence where. This index is created each time the change includes an index (for example, insert). And from this information, I can assume that an unindexed column will be faster in insertand that the index may not help in some searches, for example, regexor likematching patterns.

I am looking to have a similar or better understanding of what happens when you do one or more joins.

Answer 1

In Postgresql, the scheduler / optimizer calculates which of the following three methods to use (from the PostgreSQL documentation ):

: , . , . (, , . .)

merge join: . , . , . , .

hash join: -, -. - .