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DECODE function
DECODE function:
DECODE function works similar to if-else statement or case statement. DECODE compares expression to each search value one by one and returns the result of that search which is equal to the expression. If there is no match than...
Check Constraint
Check Constraint:
It is used to restrict the range of values that can be inserted in a column. If a column contain check constraint then only a particular range of values can be inserted in that column.
Example:
CREATE TABLE Employee(
...
Adding multiple rows with a single Insert Statement
INSERT ALL Statement:
With the help of INSERT ALL statement we can add multiple rows with a single INSERT statement. We can use this statement to insert multiple rows in one or more than one tables. It eliminates the need of writing insert sta...
BETWEEN and NOT BETWEEN Operator
BETWEEN Operator:
It is used to fetch values which lies within a range given in BETWEEN operator.
Syntax:
SELECT columnname(s)
FROM tablename
WHERE columnname BETWEEN value1 AND value2;
Example:
SELECT * FROM Employee
WHERE ...
Dual Table
Dual table:
DUAL table is a dummy table which
contains one row and one column and
by default it is present in
database.It contains a single
VARCHAR2(1) column known as DUMMY
with a value "X".
It can be accessed by all users but
the ...
Aggregate Functions
Aggregate Functions:
Oracle has many built-in functions which are used to process numbers or strings. They are very useful as we can directly use them , we just have to write the aggregate function name and in braces the column name on which w...
How to use Left Join
Left Join:
Left Join is used to join two tables and it return all rows from table 1 and matching rows from table 2. The result is NULL for unmatched rows for table 2. Left Join keyword is used to apply Left Join on two tables.
Syntax for Le...
Truncating a table
TRUNCATE TABLE Statement:
TRUNCATE Statement is used to remove all records from a table. It is a Data Definition Language (DDL) Statement as it deletes all records and only structure remains. It is similar to delete statement but without where...
Null Values
Null Values:
Null values denotes missing data in a table or a database. If a column does not have any NOT NULL constraint then for that column there can be NULL values. By default a column can have NULL values.
We cannot use comparison oper...
Sub Queries
Sub Queries:
Sub Queries are those query which comes within another query and are written after the WHERE clause.They are also known as Inner query or nested query.
It is used to return records that are used in the main query as a conditio...
DELETE Query
DELETE Statement:
It is used to delete existing records from a table. It can delete all records from a table if where condition is not given and if where condition is given than it will delete selected records which will meet the condition.
...
Having Clause
Having Clause:
The Having clause is used to filter the group result. As we cannot use Where to filter the Group By clause results so Having provide the same functionality as Where. It filter the result fetched by Group By clause. It comes a...
Group By Statement
Group By :
It is used to group the result-set by one or more column. It is used in conjunction with aggregate functions provided by Structured Query Language . If order by is used then Group By must come before Order By clause.
Syntax1:
...
Crreating Virtual Table using CREATE VIEW statement
CREATING VIEWS:
Views are virtual tables which are created from other tables .It is beneficial for those situation when we want to show limited columns to users. It can be created from one or more tables.
Syntax:
CREATE VIEW viewname AS ...
Pattern Matching Using Like Operator
LIKE Operator:
It is used to search for pattern in a table or a database . It is used with where condition. It is similar to REGEXP of MySQL.
Syntax:
SELECT columnname(s) FROM tablename WHERE columnname LIKE pattern-condition;
Examp...
Updating a column value
Updating a column value using Update Statement:
UPDATE statement is used to change the value for a column or to change multiple records using a condition. It is a data manipulation language command which are used for managing data.
Syntax:
...
To add a primary key using ALTER command
Adding a primary key using ALTER Command:
Alter command is generally used to modify table . It can be used to add columns or to remove columns. Using Alter command we can also add or remove a key from a table.
Syntax:
ALTER TABLE tablena...
To check the structure of a table
DESCRIBE Statement:
It is used to view the structure of a table means it shows name and data type of columns.
Syntax 1:
DESC tablename;
Syntax 2:
DESCRIBE tablename;
Example:
DESC Employee;
Column
Datatype
...
Eliminating Duplicates using Distinct Keyword
DISTINCT Keyword:
It is used to fetch different values from a table. It removes duplicate records from the result set and used when there can be multiple duplicate tuples in a table.
Syntax:
SELECT DISTINCT columnname FROM tablename;
...
ORDER BY Clause
Sorting the result using Order By clause:
ORDER BY clause is used to sort the data fetched using select statement either in ascending order or in descending. By default data fetched is sorted in ascending order.
Syntax:
Select columnname...
Copying Data from one table into another
INSERT INTO SELECT statement:
INSERT INTO SELECT statement is used to copy data from existing table into another table.
Syntax-1:
INSERT INTO tablename2 SELECT * FROM tablename1;
Syntax-2
INSERT INTO tablename2 (columnname(s)) ...
Inner Join
Using Inner Join:
It selects rows from both tables as long as there is a match between the column on which join is applied. Inner join is used to fetch data from more than one table.
Syntax:
SELECT columnname(s) FROM tablename1 INNER JO...
DROP Statement
DROP Statement:
With the help of drop statement we can easily delete a table or a database and it is a DML(Data Manipulation Language) command.
Syntax to drop a table:
DROP table tablename;
Example:
DROP table Employee;
It ...
Fetching Second Highest Salary
If we want to find highest salary we can use max() function simply.
Example:
SELECT max(salary) FROM Employee;
It will return the highest salary from Employee table.
But if we need to find the second highest salary then we have...
Fetch limited number of rows from a table using ROWNUM
If you want to Fetch limited numbers of rows from a table in oracle you can use Rownum.
Or in other words we can say that
It is used to return specific number of rows in a query, we can use ROWNUM in Oracle and LIMIT in MySql.
ROWNUM Synta...
Resolving physical dataguard lag online using duplicate database
Purpose --
To overcome physical standby lag online using duplicate from active database. The standby lag is huge, “incremental from scn” backup size if huge & taking long time There is no enough disk space on the Primary/standb...
NVL fuction in Oracle
NVL function helps you convert a null to an actual value.
Syntax:- NVL (expr1, expr2)
In the syntax:
expr1 is the source value or expression that may contain a null
expr2 is the target value for converting the null
Guidelines for N...
Single Row Function in Oracle (Character Function)
These functions operate on single rows only and return one result per row. There are different types of
single-row functions.
Character
Number
Date
Conversion
Single-row functions are used to manipulate data items. They accept...
