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MySQL Articles
Page 70 of 355
How will GROUP BY clause perform without an aggregate function?
When we use GROUP BY clause in the SELECT statement without using aggregate functions then it would behave like DISTINCT clause. For example, we have the following table −mysql> Select * from Student_info; +------+---------+------------+------------+ | id | Name | Address | Subject | +------+---------+------------+------------+ | 101 | YashPal | Amritsar | History | | 105 | Gaurav | Chandigarh | Literature | | 125 | Raman | Shimla | Computers | | 130 | Ram | Jhansi | Computers | | 132 | Shyam | Chandigarh ...
Read MoreHow can we start MySQL event scheduler?
Actually, MySQL event scheduler is a process that runs in the background and constantly looks for the events to execute. But before we create or schedule an event we just have to start the scheduler. It can start with the help of the following statement −mysql> SET GLOBAL event_scheduler = ON; Query OK, 0 rows affected (0.07 sec)Now with the help of the following statement, we can check its status in MySQL process list −mysql> SHOW PROCESSLIST\G *************************** 1. row *************************** Id: 3 User: root Host: localhost:49500 ...
Read MoreHow can we match the values having backslashes, like 'ab', from MySQL column?
With the help of an RLIKE operator, we can perform such kind of matching. The only concept is about to use a number of backslashes in MySQL query. The example below will make it clearer −We have the following table having values such as ‘a\b’ and ‘a\b’.mysql> select * from backslashes; +------+-------+ | Id | Value | +------+-------+ | 1 | 200 | | 2 | 300 | | 4 | a\b | | 3 | a\b | +------+-------+ 4 rows in set (0.10 sec)Now suppose if we want to match the ...
Read MoreHow can we fetch alternate even-numbered records from MySQL table?
To understand this concept we are using the data from table ‘Information’ as follows −mysql> Select * from Information; +----+---------+ | id | Name | +----+---------+ | 1 | Gaurav | | 2 | Ram | | 3 | Rahul | | 4 | Aarav | | 5 | Aryan | | 6 | Krishan | +----+---------+ 6 rows in set (0.00 sec)Now, the query below will fetch the alternate even-numbered records from the above table ‘Information’ −mysql> Select id,Name from information group by id having mod(id,2) = 0; +----+---------+ | id | Name | +----+---------+ | 2 | Ram | | 4 | Aarav | | 6 | Krishan | +----+---------+ 3 rows in set (0.00 sec)
Read MoreHow can we delete an existing MySQL event permanently?
We need to use the DROP statement to delete an existing MySQL event permanently. To illustrate it we are deleting the event named testing_event as follows −Examplemysql> DROP EVENT testing_event; Query OK, 0 rows affected (0.00 sec)
Read MoreHow can we enter numerical values as a BINARY number in MySQL statement?
Following are the two approaches with the help of which we can enter numeric values as a BINARY number −By prefix ‘B’In this approach we need to quote binary numbers within single quotes with a prefix of B. Then BINARY number string will be automatically converted into a numerical value based on the expression context.Examplemysql> Select B'1110'+0; +-----------+ | B'1110'+0 | +-----------+ | 14 | +-----------+ 1 row in set (0.00 sec)By prefix 0bIn this approach, we need to write BINARY numbers without any quotes with a prefix of 0b. Then BINARY number string will be automatically ...
Read MoreHow can we create a MySQL one-time event that executes immediately?
As we know a one-time event means the events that will be executed only once on a particular schedule. To illustrate the creation of such kind of events we are using the following example in which we are creating an event which will execute at the current time −Examplemysql> Create table event_message(ID INT NOT NULL PRIMARY KEY AUTO_INCREMENT, MESSAGE VARCHAR(255) NOT NULL, Generated_at DATETIMENOT NULL); Query OK, 0 rows affected (0.61 sec) mysql> CREATE EVENT testing_event ON SCHEDULE AT CURRENT_TIMESTAMP DO INSERT INTO event_message(message, generated_at) Values('Hello', NOW()); Query OK, 0 rows affected (0.00 sec) mysql> Select * from ...
Read MoreWhen a MySQL arithmetic expression returns NULL?
As we know that a NULL is not a value and it is also not the same as zero. MySQL arithmetic expression returns NULL if we will use NULL in it. It can be understood with the help of the following example −Examplemysql> Select 100*NULL; +----------+ | 100*NULL | +----------+ | NULL | +----------+ 1 row in set (0.00 sec) mysql> Select 100+NULL; +----------+ | 100+NULL | +----------+ | NULL | +----------+ 1 row in set (0.00 sec)From the above example, it can be observed that if we will use NULL in an arithmetic expression then the result would be NULL itself.
Read MoreHow Can we use MySQL DISTINCT clause with WHERE and LIMIT clause?
By using the WHERE clause with a DISTINCT clause in MySQL queries, we are putting a condition on the basis of which MySQL returns the unique rows of the result set. By using the LIMIT clause with a DISTINCT clause in MySQL queries, we are actually providing a perimeter to the server about a maximum number of unique rows of the result set to be returned.ExampleWe can use WHERE and LIMIT clause with DISTINCT as follows on the table named ‘testing’ −mysql> Select * from testing; +------+---------+---------+ | id | fname | Lname | ...
Read MoreHow can I get the records from MySQL table in result set in a particular way?
For getting the records from MySQL table in the result set in a particular way either ascending or descending, we need to use the ORDER BY clause along with ASC or DESC keywords. If we will not use any of the above-mentioned keywords then MySQL by default return the records in ascending order. The ORDER BY clause returned the result set based on a particular field (ascending or descending order) with which we will use the ORDER BY clause. Suppose we want to sort the rows of the following table −mysql> Select * from Student; +--------+--------+--------+ | Name | ...
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