What is joins ?

SQL joins are used to query data from two or more tables, based on a relationship between certain columns in these tables
Types of Joins

• Inner join  :
  A join that displays only the rows that have a match in both joined tables. (This is the default type of join in the Query Designer.)
   
• Outer join :
• Left outer join :
  All rows from the first-named table (the "left" table, which appears leftmost in the JOIN clause) are included. Unmatched rows in the right table do not appear. (*=)
   
• Right outer join  :
  All rows in the second-named table (the "right" table, which appears rightmost in the JOIN clause) are included. Unmatched rows in the left table are not included. (=*)
   
• Full outer join  :
  All rows in all joined tables are included, whether they are matched or not.
   
• Cross join  :
  A join whose result set includes one row for each possible pairing of rows from the two tables.

Note Columns containing NULL do not match any values when you are creating an inner join and are therefore excluded from the result set. Null values do not match other null values.