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MySQL Articles
Page 97 of 355
What MySQL returns if we pass column name, containing a NULL value, as one of the arguments of CONCAT() function?
As we know that CONCAT() function will return NULL if any of the argument of it is NULL. It means MySQL will return NULL if we pass column name, containing a NULL value, as one of the arguments of CONCAT() function. Following is an example of ‘Student’ table to explain it.ExampleIn this example, we are concatenating the values of two strings and at 5th row one, the value is NULL hence the concatenation result is also NULL.mysql> Select Name, Address, CONCAT(Name, ' Resident of ', Address)AS 'Detail of Student' from Student; +---------+---------+---------------------------+ | Name | Address | Detail ...
Read MoreWhat happens if I pass only one argument to the MySQL CONCAT() function?
MySQL allows us to pass only one argument to the CONCAT() function. In this case, MySQL returns the same argument as output. Following example will exhibit it −Examplemysql> Select Concat('Delhi'); +-----------------+ | Concat('Delhi') | +-----------------+ | Delhi | +-----------------+ 1 row in set (0.00 sec)
Read MoreUnary or Recursive Relationship
When there is a relationship between two entities of the same type, it is known as a recursive relationship. This means that the relationship is between different instances of the same entity type.Some examples of recursive relationship can be shown as follows −An employee can supervise multiple employees. Hence, this is a recursive relationship of entity employee with itself. This is a 1 to many recursive relationship as one employee supervises many employees.A person can have many children who are also persons. Hence, this is a recursive relationship of entity person with itself. This is a 1 to many recursive ...
Read MoreDDBMS Advantages and Disadvantages
The distributed database management system contains the data in multiple locations. That can be in different systems in the same place or across different geographical locations.As shown in the below example −The database is divided into multiple locations and stores the data in Site1, Site2, Site3 and Site4.The advantages and disadvantages of Distributed database management systems are as follows −Advantages of DDBMSThe database is easier to expand as it is already spread across multiple systems and it is not too complicated to add a system.The distributed database can have the data arranged according to different levels of transparency i.e data ...
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 ...
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