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Articles by Sharon Christine
Page 17 of 34
How can we create a MySQL view with a subquery?
To illustrate the making of MySQL view with subquery we are using the following data from the table ‘Cars’ −mysql> select * from cars; +------+--------------+---------+ | ID | Name | Price | +------+--------------+---------+ | 1 | Nexa | 750000 | | 2 | Maruti Swift | 450000 | | 3 | BMW | 4450000 | | 4 | VOLVO | 2250000 | | 5 | Alto | 250000 | | 6 | Skoda ...
Read MoreWhat are the different status variables in MySQL which provide us the countsnof event-related operations?
Followings are the status variables in MYSQL which provide us the counts of event-related operations −Com_create_event It provides us the number of CREATE EVENT statements executed since the last server restart.Com_alter_event − It provides us the number of ALTER EVENT statements executed since the last server restart.Com_drop_event − It provides us the number of DROP EVENT statements executed since the last server restart.Com_show_create_event − It provides us the number of SHOW CREATE EVENT statements executed since the last server restart.Com_show_events − It provides us the number of SHOW EVENTS statements executed since the last server restart.
Read MoreHow can we get the metadata of triggers?
It can be done with the help of the INFORMATION_SCHEMA database. Following statement will give us the metadata of triggers −mysql> Select trigger_schema, trigger_name, action_statement -> from information_schema.triggers\G *************************** 1. row *************************** trigger_schema: query trigger_name: trigger_before_delete_sample action_statement: BEGIN SET @count = if (@count IS NULL, 1, (@count+1)); INSERT INTO sample_rowaffected values (@count); END *************************** 2. row *************************** trigger_schema: query trigger_name: before_inser_studentage action_statement: IF NEW.age < 0 THEN SET NEW.age = 0; END IF *************************** 3. row *************************** trigger_schema: sys ...
Read MoreWhich statement, other than START TRANSACTION, is used for starting a transaction?
We can also use the BEGIN statement to start a new transaction. It is the same as the START TRANSACTION statement.Examplemysql> BEGIN; Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO Marks Values(1, 'Aarav', 'History', 40); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO Marks Values(2, 'Harshit', 'History', 48); Query OK, 1 row affected (0.00 sec) mysql> ROLLBACK; Query OK, 0 rows affected (0.04 sec)In this example, the transaction is initiated by the BEGIN Statement rather than START TRANSACTION statement. Two INSERT statements are then executed followed by a ROLLBACK statement. ROLLBACK statement will ...
Read MoreHow can MySQL REPLACE() function be used with WHERE clause?
As we know that WHERE clause is used to put condition/s in MySQL query and MySQL returns result set based on those conditions. Similarly when we use REPLACE() function with WHERE clause, the result set will depend upon the conditions provided. Following is an example by using data from the ‘Student’ table in which REPLACE() function replaces the records of a column ‘Name’ in which the value of column ‘Subject’ is ‘Computers’.Examplemysql> Select Name, REPLACE(Name, 'G', 'S') from student Where Subject = 'Computers'; +--------+------------------------+ | Name | REPLACE(Name, 'G', 'S') | +--------+------------------------+ | Gaurav | Saurav ...
Read MoreWhat is MySQL NULL-safe equal operator and how it is different from comparison operator?
MySQL NULL-safe equal operator, equivalent to standard SQL IS NOT DISTINCT FROM operator, performs an equality comparison like = operator. Its symbol is . It performs differently from the comparison operators in the case when we have NULL as both the operands. Consider the following examples to understand NULL-safe operator along with its difference with comparison operator −mysql> Select 50 50, NULL NULL, 100 NULL; +-----------+---------------+--------------+ | 50 50 | NULL NULL | 100 NULL | +-----------+---------------+--------------+ | 1 | 1 | 0 | +-----------+---------------+--------------+ 1 row in set (0.00 sec) mysql> Select 50 = 50, NULL = NULL, 100 = NULL; +---------+-------------+------------+ | 50 = 50 | NULL = NULL | 100 = NULL | +---------+-------------+------------+ | 1 | NULL | NULL | +---------+-------------+------------+ 1 row in set (0.00 sec)
Read MoreIn MySQL, what is Bit-field notation and how it can be used to write bit-field value?
Bit-field notation is the notation with the help of which we can write bit-field values. The syntax of Bit-field notation is as follows −Syntaxb’value’ OR 0bvalueHere, the value is a binary value written by using zeros and ones.The mainly Bit-filed notation is convenient for specifying values to be assigned to BIT columns of MySQL table. Following example will demonstrate it −mysql> Create table bit_testing (bittest BIT(8)); Query OK, 0 rows affected (1.09 sec) mysql> INSERT INTO bit_testing SET bittest = b'10101010'; Query OK, 1 row affected (0.07 sec) mysql> INSERT INTO bit_testing SET bittest = b'0101'; Query ...
Read MoreIn MySQL, without having BOOLEAN data type how can we show TRUE and FALSE values?
As we know that there is no BOOLEAN data type in MySQL hence by using TRUE or true, FALSE or false we can enter Boolean values in MySQL statement.Examplemysql> Select TRUE,FALSE; +------+-------+ | TRUE | FALSE | +------+-------+ | 1 | 0 | +------+-------+ 1 row in set (0.00 sec) mysql> Select true,false; +------+-------+ | TRUE | FALSE | +------+-------+ | 1 | 0 | +------+-------+ 1 row in set (0.00 sec)
Read MoreHow can I clone/duplicate the table along with its data, trigger and indexes?
For creating a new table just like old one along with its data, trigger, and indexes, we need to run following two queriesCREATE TABLE new_table LIKE old_table; INSERT new_table SELECT * from old_table;Examplemysql> Create table employee(ID INT PRIMARY KEY NOT NULL AUTO_INCREMENT, NAME VARCHAR(20)); Query OK, 0 rows affected (0.21 sec) mysql> Describe employee; +-------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+----------------+ | ID | int(11) | NO | PRI | NULL | auto_increment | | NAME | varchar(20) | ...
Read MoreZ Algorithm
This algorithm is named Z Algorithm because, in this algorithm, we need to create a Z array. The size of the Z array is the same as the text size. This array is used to store the length of longest possible substring starting from the current character of the main string. At first, the pattern and the main text are concatenated with a special symbol which is not present in the text and pattern. If the P is pattern and T is the main text, then after concatenation, it would be P$T (Assuming $ is not present in the P ...
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