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Articles by Chandu yadav
Page 50 of 81
How we have multiple stored GENERATED COLUMNS in MySQL table with CREATE TABLE statement?
It is quite possible to add multiple stored generated columns in a MySQL table. It can be illustrated with the following example as follows −Examplemysql> Create table profit1(cost int, price int, profit int AS (price-cost) STORED, price_revised int AS (price-2) STORED); Query OK, 0 rows affected (0.36 sec) mysql> Describe profit1; +---------------+---------+------+-----+---------+------------------+ | Field | Type | Null | Key | Default | Extra | +---------------+---------+------+-----+---------+------------------+ | cost ...
Read MoreHow can we use logical operators while creating MySQL views?
MySQL views can be created by using logical operators like AND, OR, and NOT. It can be illustrated with the help of following examples −Views with AND operatorAs we know that logical AND operator compares two expressions and returns true if both the expressions are true. In the following example, we are creating a view which has the conditions based on ‘AND’ operator.ExampleThe base table is Student_info having the following data −mysql> Select * from Student_info; +------+---------+------------+------------+ | id | Name | Address | Subject | +------+---------+------------+------------+ | 101 | YashPal | Amritsar | History ...
Read MoreWhat will happen to MySQL current transaction, if in the middle of that transaction, the DDL statement is executed?
The current MySQL transaction will be committed and ended when any of the DDL statement such as CREATE or DROP databases, Create, ALTER or DROP tables or stored routines is executed in the middle of the current transaction. All the database changes made in the current transaction will be made permanent and cannot be rolled back.Examplemysql> START TRANSACTION; Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO MARKS Values(6, 'Manak', 'History', 70); Query OK, 1 row affected (0.26 sec) mysql> Create table student(id int, Name Varchar(10), ); Query OK, 0 rows affected (0.84 sec)As we can see ...
Read MoreHow MySQL evaluates if we use EXISTS operator with the subquery that returns NULL?
If a subquery, used with EXIST operator, returns NULL, the expression EXIST NULL returns TRUE and MySQL returns the result based on an outer query. It can be understood with the help of simple example using the following data from table ‘Customers’ −mysql> Select * from Customers; +-------------+----------+ | Customer_Id | Name | +-------------+----------+ | 1 | Rahul | | 2 | Yashpal | | 3 ...
Read MoreWhile linking two strings, if I will add a NULL value then what would be the output of a CONCAT() function?
MySQL CONCAT() function will return a NULL if you will add a NULL value while linking two strings. Following example will demonstrate it −Examplemysql> Select CONCAT('Tutorials',NULL,'Point'); +----------------------------------+ | CONCAT('Tutorials',NULL,'Point') | +----------------------------------+ | NULL | +----------------------------------+ 1 row in set (0.06 sec) mysql> Select CONCAT('TutorialsPoint','.com',NULL); +--------------------------------------+ | CONCAT('TutorialsPoint','.com',NULL) | +--------------------------------------+ | NULL | +--------------------------------------+ 1 row in set (0.00 sec)
Read MoreWhy is it good to write the numbers in MySQL INTERVAL() function in ascending order?
Actually, INTERVAL() function uses the binary search for searching the bigger number than the number at first argument. So, that is why if we want INTERVAL() function to work efficiently the list of numbers would be in ascending order. Following is a good way to use INTERVAL() function −mysql> Select INTERVAL(50,20,32,38,40,50,55);
Read MoreHow can we combine values of two or more columns of MySQL table and get that value in a single column?
For combining values of two or more columns, we can use MySQL CONCAT() function. In this case, the arguments of the CONCAT() functions would be the name of the columns. For example, suppose we have a table named ‘Student’ and we want the name and address of the student collectively in one column then the following query can be written −mysql> Select Id, Name, Address, CONCAT(ID, ', ', Name, ', ', Address)AS 'ID, Name, Address' from Student; +------+---------+---------+--------------------+ | Id | Name | Address | ID, Name, Address | +------+---------+---------+--------------------+ | 1 ...
Read MoreHow can we assign a bit value as a number to a user variable?
As we know that the default type of a bit values assigned to user variables is binary strings but we can also assign a bit value to a number by using the following two methods −By using CAST() functionWith the help of CAST(… AS UNSIGNED) the bit value can be assigned a number. The following example will illustrate it −mysql> SET @abc = CAST(0b1000011 AS UNSIGNED); Query OK, 0 rows affected (0.00 sec) mysql> Select @abc; +------+ | @abc | +------+ | 67 | +------+ 1 row in set (0.00 sec)By adding 0(+0)The bit value can be ...
Read MoreWhat are the different commands used in MySQL?
SQL language is divided into four types of primary language statements: DML, DDL, DCL and TCL. Using these statements, we can define the structure of a database by creating and altering database objects and we can manipulate data in a table through updates or deletions. We also can control which user can read/write data or manage transactions to create a single unit of work.The four main categories of SQL statements are as follows −DML (Data Manipulation Language)DML statements affect records in a table. These are basic operations we perform on data such as selecting a few records from a table, ...
Read MoreReservoir Sampling
The Reservoir sampling is a randomized algorithm. In this algorithm, k items are chosen from a list with n different items.We can solve it by creating an array as a reservoir of size k. Then randomly pick one element from the main list and placed that item in the reservoir list. When one item is selected once, it will not be selected for next time. But his approach is not effective, we can increase the complexity by this method.In the reservoir list, copy first k items from the list, now one by one from the (k+1)th number in the list, ...
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