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
Outer-Join:
If you ask me what is the most important thing in SQL and my response
will always be “Outer Join”. This is because it has very high practical
value. It has been used a lot in the real world wherever SQL is
utilized. I want you to cram/memorize its definition word by word. I
will first give you its definition and explanation will follow
afterwards.
Figure 10: Outer Join: The plus (+) sign is used to
join two tables.
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Outer Join will give you all the records from the first table and only those records from the second table where there is a match.
It means that the total number of records in the result will be equal to
the number of records of the one table among the two having no positive
sign (+) attached with its column name in the WHERE clause. In other
words, the way you create an Outer join is very simple. First create a
Equijoin query and then place the positive sign (+) with the column name
of the table having least number of records, in the WHERE clause.
I would like to have your focus on the NULL (empty) values in the Figure
10; the one shown in the output table. These order dates are NULL
because there were no supplier ids 10002 & 10003 in the orders table.
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: