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Articles by Rishi Raj
Page 6 of 8
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 MoreHow can we automatically define the structure of MySQL table same as the structure of another table?
CREATE TABLE command with LIKE keyword will be able to define the structure of a MySQL table same as the structure of another table.SyntaxCREATE TABLE new_table LIKE 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) | YES | ...
Read MoreHow can we remove PRIMARY KEY constraint from a column of an existing MySQL table?
We can remove PRIMARY KEY constraint from a column of an existing table by using DROP keyword along with ALTER TABLE statement.ExampleSuppose we have a table ‘Player’ having a PRIMARY KEY constraint on column ‘ID’ as follows −mysql> DESCRIBE Player; +-------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+-------+ | ID | int(11) | NO | PRI | NULL | | | Name | varchar(20) | YES | | NULL | | +-------+-------------+------+-----+---------+-------+ 2 rows in ...
Read MoreTernary Search
Like the binary search, it also separates the lists into sub-lists. This procedure divides the list into three parts using two intermediate mid values. As the lists are divided into more subdivisions, so it reduces the time to search a key value.The complexity of Ternary Search TechniqueTime Complexity: O(log3 n)Space Complexity: O(1)Input and OutputInput: A sorted list of data: 12 25 48 52 67 79 88 93 The search key 52 Output: Item found at location: 3AlgorithmternarySearch(array, start, end, key)Input − An sorted array, start and end location, and the search keyOutput − location of the key (if found), otherwise wrong ...
Read MoreTroubleshooting tips
Following steps are mostly required to Troubleshoot any problem that occurred in production.As the first step, get the time frame from the user when a particular issue occurred. Get the logs for that particular time period.If logs are very large in size, use grep command to filter out errors.$ grep -o "\w*Exception" error.log | sort -r | uniq -cIt will help to get all the exceptions in error.log sorted in reversed order and give the unique result and with counts.
Read MoreWhat is the difference between transient and volatile in Java?
transient: An instance variable is marked transient to indicate the JVM to skip the particular variable when serializing the object containing it. This modifier is included in the statement that creates the variable, preceding the class or data type of the variable.Examplepublic transient int limit = 55; // will not persist public int b; // will persistvolatile: The volatile modifier is used to let the JVM know that a thread accessing the variable must always merge its own private copy of the variable with the master copy in the memory.Accessing a volatile variable synchronizes all the cached copied ...
Read MoreWhat is the difference between String s1 = "Hello" and String s1= new String("Hello") in java?
When you store a String asString str1 = "Hello";directly, then JVM creates a String object with the given value in a separate block of memory known as String constant pool.And whenever we try to create another String asString str2 = "Hello";JVM verifies whether any String object with the same value exists in the String constant pool, if so, instead of creating a new object JVM assigns the reference of the existing object to the new variable.And when we store String asString str = new String("Hello");using the new keyword, a new object with the given value is created irrespective of the ...
Read MoreJava ResultSet findColumn() method with example
When we execute certain SQL queries (SELECT query in general) they return tabular data.The java.sql.ResultSet interface represents such tabular data returned by the SQL statements.i.e. the ResultSet object holds the tabular data returned by the methods that execute the statements which quires the database (executeQuery() method of the Statement interface in general).The ResultSet object has a cursor/pointer which points to the current row. Initially this cursor is positioned before first row.The findColumn() method of the ResultSet interface maps the column label to column index. Using this you can find the index of a particular column in the result set.This method accepts a String ...
Read MoreJava ResultSet relative() method with example
When we execute certain SQL queries (SELECT query in general) they return tabular data.The java.sql.ResultSet interface represents such tabular data returned by the SQL statements.i.e. the ResultSet object holds the tabular data returned by the methods that execute the statements which quires the database (executeQuery() method of the Statement interface in general).The ResultSet object has a cursor/pointer which points to the current row. Initially this cursor is positioned before first row.The relative() method of the ResultSet interface moves the ResultSet pointer/cursor n number of rows from the current position.This method returns an integer value representing the current row number to which the ResultSet pointer ...
Read MoreJava ResultSetMetaData getColumnCount() method with example?
The getColumnCount() method of the ResultSetMetaData (interface) retrieves the number of the columns of the current ResultSet object.This method returns an integer value representing the number of columns.To get the ResultSetMetaData object, you need to:Register the Driver: Select the required database register the Driver class of the particular database using the registerDriver() method of the DriverManager class or, the forName() method of the class named Class.DriverManager.registerDriver(new com.mysql.jdbc.Driver());Get connection: Create a connection object by passing the URL of the database, username and password of a user in the database (in string format) as parameters to the getConnection() method of the DriverManager class.Connection mysqlCon = ...
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