Oracle SQL in 10 Minutes - Asim Abbasi
CH1: SQL Basics | CH2: SQL Operators | CH3: SQL Built-in Functions | CH4: SQL Joins | CH5: UPDATE, INSERT & DELETE Statements | CH6: CREATE, ALTER & DROP Statements | CH7: Constraints | CH8: Linking Tables vs Joining Tables | CH9: SQL Statements for Other Database Objects | CH10: SQL Statements for Database Security
Chapter 4: SQL Joins
Extracting Data from Multiple Tables:
Joins help in extracting data from two or more tables based on some
condition specified in the WHERE clause. The very important point to
note over here is that Joins are only at the query level. It means the
output that you see as a result of statement containing any form of
“Join”, is only for that instance and its in the volatile memory (RAM).
Figure 8: Joining two or more tables.
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There are following different kinds of Joins and each having its own application. Out of these, two are having extremely high importance viz., Equi-Join and Outer-Join.
Self Joins
Cartesian Products
Equijoins
Outer Joins
SELECT statements containing Joins should not be confused with
“Primary/Foreign” key relationship between the tables commonly known as
Linking Tables which we will discuss later in this chapter. Just keep in
mind whether you have established a primary/foreign key relationship
between the tables or not, you can still run the SELECT statements
containing joins against those tables.
Chapter 4: SQL Joins
CH1: SQL Basics | CH2:
SQL Operators |
CH3: SQL Built-in Functions | CH4:
SQL Joins | CH5:
UPDATE, INSERT & DELETE Statements |
CH6: CREATE, ALTER & DROP Statements | CH7:
Constraints | CH8:
Linking Tables vs Joining Tables | CH9:
SQL
Statements for Other Database Objects | CH10:
SQL Statements for
Database Security Share with others: