Article Categories
- All Categories
-
Data Structure
-
Networking
-
RDBMS
-
Operating System
-
Java
-
MS Excel
-
iOS
-
HTML
-
CSS
-
Android
-
Python
-
C Programming
-
C++
-
C#
-
MongoDB
-
MySQL
-
Javascript
-
PHP
-
Economics & Finance
Database Articles
Page 285 of 547
Mobile Databases
Mobile databases are separate from the main database and can easily be transported to various places. Even though they are not connected to the main database, they can still communicate with the database to share and exchange data.The mobile database includes the following components −The main system database that stores all the data and is linked to the mobile database.The mobile database that allows users to view information even while on the move. It shares information with the main database.The device that uses the mobile database to access data. This device can be a mobile phone, laptop etc.A communication link ...
Read MoreMultidimensional Databases
Multidimensional databases are used mostly for OLAP (online analytical processing) and data warehousing. They can be used to show multiple dimensions of data to users .A multidimensional database is created from multiple relational databases. While relational databases allow users to access data in the form of queries, the multidimensional databases allow users to ask analytical questions related to business or market trends.The multidimensional databases uses MOLAP (multidimensional online analytical processing) to access its data. They allow the users to quickly get answers to their requests by generating and analysing the data rather quickly.The data in multidimensional databases is stored in ...
Read MoreHow does MySQL handle overflow during numeric expression assessment?
As we know that MySQL will produce an error if overflow occurs during the assessment of numeric expressions. For example, the largest signed BIGNT is 9223372036854775807, so the following expression will produce an error −mysql> Select 9223372036854775807 + 1; ERROR 1690 (22003): BIGINT value is out of range in '(9223372036854775807+1)'MySQL can handle such kind of overflows in following ways:BY CONVERTING VALUE TO UNSIGNEDMySQL enables such kind of operations by converting the values to unsigned as follows −mysql> Select CAST(9223372036854775807 AS UNSIGNED) +1; +------------------------------------------+ | CAST(9223372036854775807 AS UNSIGNED) +1 | +------------------------------------------+ | ...
Read MoreWhat MySQL returns when we alter AUTO_INCREMENT value which is less than current sequence number?
When we use AUTO_INCREMENT on a MySQL column, the sequence number always increases in ascending order starting from the default value 1 or from the value we specify.That is the reason, MySQL does not allow changing the AUTO_INCREMENT value to a value which is less than the current sequence number. It can be understood with the help of the following example −ExampleIn this example suppose we have a table named ‘emp1’ and while creating the table we specify the AUTO_INCREMENT VALUE to 100. Hence after inserting the values in table, the sequence would start from 100 onwards as can be ...
Read MoreWhat would be the effect on the output of MySQL LAST_INSERT_ID() function in the case on multiple-row insert?
As we know that MySQL LAST_INSERT_ID() function returns the latest generated sequence number but in case of multiple row-insert it would return the sequence number generated by the foremost inserted row.Examplemysql> Insert into Student(Name) values('Ram'), ('Mohan'), ('Aryan'); Query OK, 3 rows affected (0.03 sec) Records: 3 Duplicates: 0 Warnings: 0The query above inserts three values in Student table with the help of Multiple-row insert query. The value of Column ‘Id’ can be checked with the help of the following query −mysql> Select * from Student; +----+-------+ | Id | Name | +----+-------+ | 1 | Raman | | 2 | ...
Read MoreWhat is the use of MySQL LAST_INSERT_ID() function?
MySQL LAST_INSERT_ID() function is used to obtain the most recent generated sequence number by AUTO_INCREMENT.ExampleIn this example, we are creating a table named ‘Student’ having an AUTO_INCREMENT column. We insert two values in the column ‘Name’ and when we use INSERT_LAST_ID() function then it returns the most recent generated sequence number i.e. 2.mysql> Create table Student(Id INT PRIMARY KEY NOT NULL AUTO_INCREMENT, Name Varchar(5)); Query OK, 0 rows affected (0.13 sec) mysql> Insert into student(Name) Values('Raman'); Query OK, 1 row affected (0.06 sec) mysql> Insert into student(Name) Values('Rahul'); Query OK, 1 row affected (0.07 sec) mysql> Select* ...
Read MoreWhat is the use of NCHAR in MySQL?
MySQL defines NCHAR as a way to indicate that a CHAR column should use predefined character set. Utf8 is used by MySQL as its predefined character set.ExampleIn the example below, we are creating a table named ‘Student1’. In this table, we are declaring the data types of three columns with three different declaration styles which are rather equivalent of each other. It is all due to NCHAR.mysql> Create table Student1(Name Char(10) character set utf8, Address NATIONAL CHARACTER(10), FatherName NCHAR(10)); Query OK, 0 rows affected (0.25 sec)Now on checking the status of table, with the help of query below, we ...
Read MoreHow can we insert a new row into a MySQL table?
With the help of INSERT INTO command, a new row can be inserted into a table.SyntaxINSERT INTO table_name values(value1, value2, …)ExampleSuppose we have a table named ‘Employee’ with three columns ‘Emp_id’, ‘Emp_name’ and ‘Emp_Sal’ then with the help of following query we can add new rows to the table −mysql> INSERT INTO Employee values(110, 'Aarav', 50000); Query OK, 1 row affected (0.07 sec) mysql> INSERT INTO Employee values(200, 'Raman', 28000); Query OK, 1 row affected (0.10 sec) mysql> Select * from Employee; +---------+-------------+-----------+ | Emp_id | Emp_name | Emp_sal | +---------+-------------+-----------+ | 110 |Aarav ...
Read MoreHow MySQL reacts when we specify a CHARACTER SET binary attribute for a character string data type?
On specifying a CHARACTER SET binary attribute for a character string data type, MySQL creates that column as its subsequent binary string type. The conversions for CHAR, VARCHAR and BLOB data types take place as follows −CHAR would become BINARYVARCHAR would become VARBINARYTEXT would become BLOBThe above kind of conversion does not occur for ENUM and SET data type and they both are created as declared while creating the table.ExampleIn the example below we have created a table named ‘EMP’ with four columns all specified as CHARACTER SET binary as follows −mysql> Create table Emp(Name varchar(10) CHARACTER SET binary, Address ...
Read MoreOn inserting 'NULL', '0' or No Value to the column, will MySQL assign sequence number for AUTO_INCREMENT column?
MySQL will automatically assign sequence numbers to the AUTO_INCREMENT column even if we insert NULL, 0 or No Value to the column in a table.Examplemysql> create table test123(id INT PRIMARY KEY NOT NULL AUTO_INCREMENT, Name Varchar(10)); Query OK, 0 rows affected (0.15 sec)The query above created a MySQL table named ‘test123’ with columns named ‘id’ and ‘Name’. The column ‘id’ is declared AUTO_INCREMENT. Now, if we insert ‘No Value’, ‘0’ or ‘NULL’ in the ‘Name’ column, MySQL will assign the sequence numbers to column ‘id’. It can be seen from the result queries below −mysql> Insert Into test123(Name) values(''), ('0'), ...
Read More