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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 trigger_name: sys_config_insert_set_user action_statement: BEGIN IF @sys.ignore_sys_config_triggers != true AND NEW.set_by ... Read More
Declaring a column ‘NOT NULL’ means that this column would not accept NULL values but zero (0) and an empty string is itself a value. Hence there would be no issue if we want to insert zero or an empty string into a MySQL column which is defined as NOT NULL. Following comparisons of 0 and empty string with NULL would make it clear −mysql> Select 0 IS NULL, 0 IS NOT NULL; +-----------+---------------+ | 0 IS NULL | 0 IS NOT NULL | +-----------+---------------+ | 0 | 1 | ... Read More
By executing SELECT @@TX_ISOLATION command we can check the current MySQL transaction isolation level.Examplemysql> SELECT @@TX_ISOLATION; +-----------------+ | @@TX_ISOLATION | +-----------------+ | REPEATABLE-READ | +-----------------+ 1 row in set (0.00 sec)
The representation of an empty string in result set depends on data type when we insert an empty string into a MySQL column which is declared as NOT NULL. As we know that on inserting empty string we are providing value to MySQL that has integer representation as INT 0.Now, if that column is having INTEGER data type then MySQL would show 0 in the result set as that empty string has been mapped to zero as an integer.Examplemysql> create table test(id int NOT NULL, Name Varchar(10)); Query OK, 0 rows affected (0.19 sec) mysql> Insert into test(id, name) ... Read More
FROM clause after SELECT shows the references to a table. But if there is no reference to any table then we can use SELECT without the FROM clause. In other words, we can say that SELECT can be used to retrieve rows computed without reference to any table. Consider the following statements −mysql> Select concat_ws(" ","Hello", "World"); +---------------------------------+ | concat_ws(" ","Hello", "World") | +---------------------------------+ | Hello World | +---------------------------------+ 1 row in set (0.00 sec) mysql> Set @var1=100; Query OK, 0 rows affected (0.00 sec) mysql> Select @var1; +-------+ | @var1 | +-------+ | 100 | +-------+ 1 row in set (0.00 sec)
As we know that a query can have multiple MySQL statements followed by a semicolon. Suppose if we want to get the result from multiple tables then consider the following example to get the result set from ‘Student_info’ and ‘Student_detail’ by writing a single query −mysql> Select Name, Address from Student_info; Select Studentid, Address from Student_detail; +---------+------------+ | Name | Address | +---------+------------+ | YashPal | Amritsar | | Gaurav | Chandigarh | | Raman | Shimla | | Ram | Jhansi | | Shyam | Chandigarh | | ... Read More
Use a while loop to input multiple values from the user in one line.Let’s say you need to get the elements of a matrix. Get it using Console.ReadLine() as shown below −Console.Write("Enter elements - Matrix 1 : "); for (i = 0; i < m; i++) { for (j = 0; j < n; j++) { arr1[i, j] = Convert.ToInt16(Console.ReadLine()); } }The following is an example showing how we can input multiple values from user −Example Live Demousing System; namespace Demo { public class Program { public static void Main(string[] args) ... Read More
‘\c’ option means ‘clear’ and is used to clear the current input. Suppose if we do not want to execute a command that we are entering, then we can use a clear \c option which clears the current input. For example, the use of \c option can be done as follows −mysql> Select * -> from\cIn the example above, when we use \c in a statement, MySQL clears the current input and returns back to the MySQL prompt for accepting other statements.
Following example compares two strings by using str compareTo (string), str compareToIgnoreCase(String) and str compareTo(object string) of string class and returns the ascii difference of first odd characters of compared strings.Example Live Demopublic class StringCompareEmp{ public static void main(String args[]) { String str = "Hello World"; String anotherString = "hello world"; Object objStr = str; System.out.println( str.compareTo(anotherString) ); System.out.println( str.compareToIgnoreCase(anotherString) ); System.out.println( str.compareTo(objStr.toString())); } }OutputThe above code sample will produce the following result.-32 0 0String compare by equals()This method compares ... Read More
Following example uses iterator Method of Collection class to iterate through the HashMap.Example Live Demoimport java.util.*; public class Main { public static void main(String[] args) { HashMap< String, String> hMap = new HashMap< String, String>(); hMap.put("1", "1st"); hMap.put("2", "2nd"); hMap.put("3", "3rd"); Collection cl = hMap.values(); Iterator itr = cl.iterator(); while (itr.hasNext()) { System.out.println(itr.next()); } } }OutputThe above code sample will produce the following result.1st 2nd 3rd