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To initialize a dictionary to an empty dictionary, use the Clear() method. It clears the dictionary and forms it as empty.dict.Clear();After that, use the Dictionary count property to check whether the list is empty or not −if (dict.Count == 0) { Console.WriteLine("Dictionary is empty!"); }Let us see the complete code −Example Live Demousing System; using System.Collections.Generic; using System.Linq; namespace Demo { public class Program { public static void Main(string[] args) { var dict = new Dictionary < string, string > (); dict.Clear(); if (dict.Count == 0) { Console.WriteLine("Dictionary is empty!"); } } } }OutputDictionary is empty!
Sets in C# is a HashSet. HashSet in C# eliminates duplicate strings or elements in an array. In C#, it is an optimized set collectionTo declare HashSet −var h = new HashSet(arr1);Above, we have set the already declared array arr1 in the HashSet.Now set it on the array to remove the duplicate words −string[] arr2 = h.ToArray();Let us see an example to remove duplicate strings using C# HashSet.Here, we have duplicate elements −Exampleusing System; using System.Collections.Generic; using System.Linq; class Program { static void Main() { string[] arr1 = {"Table", "Chair", "Pen", "Clip", "Table"}; ... Read More
Actually ‘FOR EACH ROW’ means for each of the matched rows that get either updated or deleted. In other words, we can say that trigger is not applied to each row, it just says to execute the trigger body for each affected table row. We can illustrate this by the following example −ExampleIn this example, we are creating two tables, Sample and Sample_rowaffected, as follows −mysql> Create table Sample(id int, value varchar(20)); Query OK, 0 rows affected (0.47 sec) mysql> Insert into Sample(id, value) values(100, 'same'), (101, 'Different'), (500, 'excellent'), (501, 'temporary'); Query OK, 4 rows affected (0.04 sec) ... Read More
Actually, MySQL determines the end of the statement when it got termination semicolon. Suppose if we are writing a single statement in different lines then after writing the first line, MySQL changes promptly from ‘mysql>’ to ‘->’ which indicates that MySQL has not seen a complete statement yet and is waiting for the rest. When it got semicolon then MySQL executes the statement. It can be understood with the help of the following example −Examplemysql> Select Id, Name -> From -> Student_info -> ; +------+---------+ | Id | Name | +------+---------+ ... Read More
If there is ‘empty set’ in the result set of MySQL query then it means that MySQL is returning no rows and no error also in the query. It can be understood with the help of the following example −mysql> Select * from Student_info WHERE Name = 'ABCD'; Empty set (0.00 sec)We can see the empty set and execution time as output. It means that the query is correct but the MySQL table is not having the name ‘ABCD’.
With the help of the SHOW TRIGGERS statement, we can list all the triggers in a particular database. It can be illustrated with the help of the following example −Examplemysql> Show Triggers\G *************************** 1. row *************************** Trigger: trigger_before_delete_sample Event: DELETE Table: sample Statement: BEGIN SET @count = if (@count IS NULL, 1, (@count+1)); INSERT INTO sample_rowaffected values (@count); END Timing: BEFORE Created: 2017-11-21 12:31:58.70 sql_mode: ONLY_FULL_GROUP_BY, STRICT_TRANS_TABLES, NO_ZERO_IN_DATE, NO_ZERO_DATE, ERR OR_FOR_DIVISION_BY_ZERO, NO_AUTO_CREATE_USER, NO_ENGINE_SUBSTITUTION Definer: root@localhost character_set_client: cp850 collation_connection: cp850_general_ci Database Collation: latin1_swedish_ci *************************** 2. ... Read More
With the help of \c command, we can discard a MySQL statement in the middle of its processing. Consider the following example in which in the middle of the statement we want to discard it then we use \c option for it −mysql> Select * -> from\c mysql>The above query shows that after using \c option MySQL discards the statement and returns to the prompt.
We must have to understand the advantages, disadvantages, and restrictions of using MySQL triggers so that we can use it effectively.AdvantagesFollowings are the advantages of using MySQL triggers −Integrity of data − With the help of MySQL trigger we can check the integrity of data in the table. In other words, MySQL triggers are the alternative way to check the integrity of data.Useful for catching errors − MySQL triggers can catch errors in business logic in the database layer.Alternative way to run scheduled tasks − Actually by using MySQL triggers we do not have to wait to run the scheduled tasks because ... Read More
With the help of following MySQL statement, we can use SELECT to calculate the expression −SELECT expression;The above statement is having no reference to any table. Followings are some examples −mysql> Select 10 DIV 5; +----------+ | 10 DIV 5 | +----------+ | 2 | +----------+ 1 row in set (0.06 sec) mysql> Select 10*5; +------+ | 10*5 | +------+ | 50 | +------+ 1 row in set (0.00 sec) mysql> Set @var1 = 100, @var2 = 200; Query OK, 0 rows affected (0.00 sec) mysql> Select @Var1+@Var2; +-------------+ | @Var1+@Var2 | +-------------+ | 300 | +-------------+ 1 row in set (0.00 sec)
We can get the summary output of a column in MySQL result set by using the “WITH ROLLUP” modifier. This modifier is used with GROUP BY CLAUSE. It gives the summary output to include extra rows that represent higher-level summary operations.ExampleIn this example, the WITH ROLLUP modifier gave the summary output with total cost value in the extra row.mysql> Select Item_name, SUM(Cost) AS Total_cost from Item_list GROUP BY Item_name WITH ROLLUP; +-----------+------------+ | Item_name | Total_cost | +-----------+------------+ | Notebook | 45.00 | | Pen | 31.70 | | Pencilbox | 125.20 | | NULL | 201.90 | +-----------+------------+ 4 rows in set (0.00 sec)