by Dinesh Thakur Category: SQL Queries

Use the LIKE condition to perform wildcard searches of valid search string values. Search conditions can contain either literal characters or numbers. You can combine pattern-matching characters. You can use the ESCAPE identifier to search for the actual % and _ symbols.

 
by Dinesh Thakur Category: SQL Queries

The EXISTS condition is considered "to be met" if the subquery returns at least one row. EXISTS operator simply tests whether the inner query returns any row. If it does, then the outer query proceeds. If not, the outer query does not execute, and the entire SQL statement returns nothing.

 
by Dinesh Thakur Category: SQL Queries

The PRIMARY KEY constraint uniquely identifies each record in a database table. Primary keys must contain unique values. A primary key column cannot contain NULL values. Each table should have a primary key, and each table can have only one primary key.



 
by Dinesh Thakur Category: SQL Queries

Check constraint is used to validate values entered into a column. CHECK constraints enforce domain integrity by limiting the values that are accepted by a column. They are similar to FOREIGN KEY constraints in that they control the values that are placed in a column. The difference is in how they determine which values are valid: FOREIGN KEY constraints get the list of valid values from another table.

 
by Dinesh Thakur Category: SQL Queries

By default all columns in a table can contain null values. If you want to ensure that a column must always have a value, i.e. it should not be left blank, then define a NOT NULL constraint on it.

 
by Dinesh Thakur Category: SQL Queries

A UNIQUE key integrity constraint requires that every value in a column or set of columns (key) be unique-that is, no two rows of a table have duplicate values in a specified column or set of columns.

 
by Dinesh Thakur Category: SQL Queries

In SQL the UNION Clause combines the results of two SQL queries into a single table of all matching rows. The two queries must have the same number of columns and compatible data types to unite. Any duplicate records are automatically removed unless UNION ALL is used.



 
by Dinesh Thakur Category: SQL Queries

The HAVING Clause was added to SQL because the WHERE keyword could not be used with aggregate functions. As we know that WHERE clause is used to restrict the number of rows fetched from the table. But if we try to restrict the number of groups with where clause it will generate an error message. So we can use having clause to divide the groups with Group by clause.

 
by Dinesh Thakur Category: SQL Queries

You can rename a table or a column temporarily by giving another name known as alias. The term alias means an alternate name. Here’s an example of how to use a column alias

 
by Dinesh Thakur Category: SQL Queries

Sometimes we may decide that we need to get rid of a table in the database for some reason. The SQL DROP TABLE statement is the SQL command that removes an entire SQL table. This command also removes one or more table definitions and all data, indexes, triggers, constraints, and permission specifications for those tables.



 
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 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

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 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 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 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 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

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.

 

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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 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.