Join Types Flashcards
Describe LEFT Join.
Describe EQUI Join.
Describe THETA Join.
Left Join: Returns all records from the left table, and the matched records from the right table. So basically, all left records will appear, and the only records in the right table that will appear will be ones that match based on the Join condition. Make sense? Yes.
Equi Join: Basically just a regular join. Only shows the columns which actually match, that’s it.
Theta Join: Right listen here. If equi join is “JOIN ON =“ then this is “JOIN ON >”, basically instead of equals, you use a different operator such as greater than. Note: this also includes operators like “greater than or equal to”.
What is referential integrity?
This refers to all tables being correctly linked through relationships and keys to the point where all JOINS return the data they should.
