Thus far we have only been getting data from one table at a time. This is fine for simple tasks, but in most real world SQL usage you will often need to get data from multiple tables in a single query. Oracle provides the facility to retrieve the data from multiple tables with the help of joins. It is perhaps a wonderful feature of SQL that permit to retrieve the data from multiple users. [Read more…] about SQL Using Joins
SQL INNER JOIN
In SQL inner joins are also called simple joins or equijoin. We are now ready to present a SELECT statement with what is called an inner join: [Read more…] about SQL INNER JOIN
SQL Self JOIN
A self-join is a query in which a table is joined (compared) to itself. Self-joins are used to compare values in a column with other values in the same column in the same table. The SQL self-join can be done by using table aliases to cheat one table like a different table and then join them together. [Read more…] about SQL Self JOIN
SQL RIGHT JOIN Keyword
A right outer join (or right join) closely resembles a left outer join, except with the treatment of the tables reversed. Every row from the “right” table (B) will appear in the Joined table at least once. If no matching row from the “left” table (A) exists, NULL will appear in columns from A for those records that have no match in A. [Read more…] about SQL RIGHT JOIN Keyword
SQL: Types of Joins
It is important to note that the INNER JOIN only returns data where a match is found. While using the inner join we have seen that if there exists certain records in one table. Which doesn’t have corresponding values in the second table then those rows will not be selected. [Read more…] about SQL: Types of Joins
SQL LEFT OUTER JOIN
The result of a left outer join (or simply left join) for table A and B always contains records of the “left” table (A), even if the join-condition does not find any matching record in the “right” table (B). This means that if the ON clause matches 0 (zero) records in B, the join will still return a row in the result-but with NULL in each column from B. [Read more…] about SQL LEFT OUTER JOIN
SQL FULL OUTER JOIN Keyword
To retrieve the Employee name, job, salary, deptno, dname from EMP, DEPT table. It will return all information regarding the employees and the department information. This is Full Outer Join’s Example. [Read more…] about SQL FULL OUTER JOIN Keyword
SQL CROSS JOIN
A cross join, or product provides the foundation upon which all types of inner joins operate. A cross join returns the Cartesian product of the sets of records from the two joined tables. Thus, it equates to an inner join where the join-condition always evaluates to true or join-condition is absent in statement. This command is introduced for Oracle9i. If A and B are two sets, then the cross join is written as A x B. [Read more…] about SQL CROSS JOIN
SQL CREATE INDEX Statement and Types of Indexes
When the user fires a SELECT statement to search for a particular record, the oracle engine must first locate the table on the hard disk. The Oracle engine reads the information and locates the starting location of a table’s record on the current storage media. [Read more…] about SQL CREATE INDEX Statement and Types of Indexes
SQL DROP INDEX
The SQL DROP INDEX statement is the SQL command that removes an entire SQL index. You may drop an index permanently when it is no longer useful or temporarily. If the index is harming or not helping performance it could be dropped. [Read more…] about SQL DROP INDEX