Creating Natural Joins

• The NATURAL JOIN clause is based on all columns in the two tables that have the same name
• It selects rows from the two tables that have equal values in all matched columns
• If the columns having the same names have different data types, an error is returned

Retrieving Records with Natural Joins :

• SELECT empno, dname,loc FROM emp NATURAL JOIN dept ;

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Creating Joins with the USING Clause :

• If several columns have the same names but the data types do not match, the NATURAL JOIN clause can be modified with the USING clause to specify the columns that should be used for an equijoin
• Use the USING clause to match only one column when more than one column matches
• Do not use a table name or alias in the referenced columns
• The NATURAL JOIN and USING clauses are mutually exclusive

Joining Column Names :



Retrieving Records with the USING Clause :

• SELECT emp.empno, emp.ename, dept.loc, deptno FROM emp JOIN dept USIN (deptno) ;

Displaying Data from Multiple Tables

Obtaining Data from Multiple Tables :



Types of Joins :

• Joins that are compliant with the SQL:1999 standard include the following :

1. Cross joins
2. Natural joins
3. USING clause
4. Full (or two-sided) outer joins
5. Arbitrary join conditions for outer joins

Joining Tables Using SQL : 1999 Syntax

• Use a join to query data from more than one table

SELECT table1.column, table2.column FROM table1 [NATURAL JOIN table2] | [JOIN table2 USING (column_name)] | [JOIN table2 ON (table1.column_name = table2.column_name)]| [LEFT|RIGHT|FULL OUTER JOIN table2 ON (table1.column_name = table2.column_name)]| [CROSS JOIN table2];