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by Dinesh Thakur Category: SQL Queries

Null is a special marker used in Structured Query Language (SQL) to indicate that a data value does not exist in the database. NULL means missing information and inapplicable information". NULL values represent missing unknown data. By default, a table column can hold NULL values.



 
by Dinesh Thakur Category: SQL Queries

The DEFAULT constraint is used to insert a default value into a column. The default value will be added to all new records, if no other value is specified. You can also specify the DEFAULT value for columns i.e. when user does not enter anything in that column then that column will have the default value. Default constraints are ANSI -standard constraints you can assign to a column either with the CREATE TABLE or ALTER TABLE statements.

 
by Dinesh Thakur Category: SQL Queries

The SQL BETWEEN & AND operator selects a range of data between two values. You can also use the BETWEEN function with dates. The BETWEEN function can also be combined with the NOT operator

 
by Dinesh Thakur Category: SQL Queries

The MINUS query will compare each record in statementl to a record in statement2. The result returned will be records in Select Statement I that are not in Select statement2.

 
by Dinesh Thakur Category: SQL Queries

Similar to the UNION command, INTERSECT also operates on two SQL statements. The difference is that, while UNION essentially acts as an OR operator (value is selected if it appears in either the first or the second statement), the INTERSECT command acts as an AND operator (value is selected only if it appears in both statements).

 
by Dinesh Thakur Category: SQL Queries

The IN operator allows you to specify multiple values in a WHERE clause. The IN function helps reduce the need to use multiple OR conditions. The SQL IN clause allows you to specify discrete values in your SQL WHERE search criteria. The syntax for using the IN keyword is as follows:

 
by Dinesh Thakur Category: SQL Commands

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.

 
by Dinesh Thakur Category: SQL Commands

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.



 
by Dinesh Thakur Category: SQL Commands

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.



 
by Dinesh Thakur Category: SQL Commands

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.

 

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About Dinesh Thakur

Dinesh ThakurDinesh Thakur holds an B.SC (Computer Science), MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular Computer Notes blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to contact us.



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