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Articles by karthikeya Boyini
Page 124 of 143
C++ Program to Implement Hash Tables
A hash table is a data structure which is used to store key-value pairs. Hash function is used by hash table to compute an index into an array in which an element will be inserted or searched.This is a C++ program to Implement Hash Tables.AlgorithmBegin Initialize the table size T_S to some integer value. Create a structure hashTableEntry to declare key k and value v. Create a class hashMapTable: Create a constructor hashMapTable to create the table. Create a hashFunc() function which return key mod T_S. Create a function Insert() to insert element at ...
Read MoreDoes MySQL support table inheritance?
MySQL uses foreign key constraint instead of inheritance. MySQL does not support table inheritance.You can achieve the same with the help of foreign key constraint. Let us create a table and use the foreign key constraint. The query to create the first table is as follows −mysql> create table Parent_Table -> ( -> ParentId int, -> PRIMARY KEY(ParentId) -> ); Query OK, 0 rows affected (3.59 sec)Now create the second table. The query to create the second table is as follows −mysql> create table Child_Table ...
Read MoreHow to fix poor performance of INFORMATION_SCHEMA.key_column_usage in MySQL?
You can use GLOBAL variable as shown below −SET global innodb_stats_on_metadata =0;After including the above syntax, the INFORMATION_SCHEMA.key_column_usage will take less time and that would improve the performance.The query is as follows −mysql> set global innodb_stats_on_metadata =0; Query OK, 0 rows affected (0.00 sec) mysql> SELECT REFERENCED_TABLE_NAME,TABLE_NAME,COLUMN_NAME,CONSTRAINT_SCHEMA -> FROM INFORMATION_SCHEMA.key_column_usage;The following is the output −It returns 674 rows in 0.28 seconds.
Read MoreCorrectly implement the AND condition in MySQL
To implement AND condition, the syntax is as follows −select *from yourTableName where yourColumnName1 = yourValue1 AND yourColumnName2 = yourValue2;To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table MySQLANDConditionDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Name varchar(100), -> Age int -> ); Query OK, 0 rows affected (0.80 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into MySQLANDConditionDemo(Name, Age) values('Larry', 23); Query OK, 1 row affected (0.11 sec) mysql> ...
Read MoreHow do I get the average string length in MySQL?
To get the average string length in MySQL, we will work around a query that gets rows from 1 to 10 and displays the result.Let us first create a table. The query to create a table is as follows −mysql> create table AverageString -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Value varchar(20) -> ); Query OK, 0 rows affected (0.66 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into AverageString(Value) values('MySQL Query'); Query OK, 1 row ...
Read MoreWhat does % stand for in host column and how to change user's password?
The localhost means you can access from same machine while from % the remote host access is possible. The syntax is as follows to change the user password.SET PASSWORD FOR 'yourUserName'@'localhost' ='yourPassword';First check the user and host from MySQL.user table. The query is as follows −mysql> select user, host from MySQL.user;Here is the output −+------------------+-----------+ | user | host | +------------------+-----------+ | Bob | % | | Manish | % ...
Read MoreSet Optimal MySQL configuration in my.cnf?
First, you need to open my.cnf file. The following is the query to get the directory location of the config file on Windows −mysql> select @@datadir;Output+---------------------------------------------+ | @@datadir | +---------------------------------------------+ | C:\ProgramData\MySQL\MySQL Server 8.0\Data\ | +---------------------------------------------+ 1 row in set (0.00 sec)Here is the snapshot of the directory −Now open my.cnf file. The snapshot is as follows −If you want to add more data to cache, ...
Read MoreHow do you get the last access (and/or write) time of a MySQL database?
To get the last access time, try the following syntax −SELECT update_time FROM INFORMATION_SCHEMA.TABLES WHERE table_schema = 'yourDatabaseName' AND table_name = 'yourTableName'The above syntax gives the last access information about MyISAM engine type.Here, our database is ‘business’ and we will be using the table with the name ‘twoprimarykeytabledemo'.To get last access time of MySQL database, use the following query.Case 1 − The query is as follows −mysql> SELECT update_time -> FROM INFORMATION_SCHEMA.TABLES -> WHERE table_schema = 'business' -> AND table_name = 'twoprimarykeytabledemo';The output is as follows −+---------------------+ | UPDATE_TIME ...
Read MoreHow to check whether a stored procedure exist in MySQL?
Let us first create a stored procedure −mysql> DELIMITER // mysql> CREATE PROCEDURE ExtenddatesWithMonthdemo(IN date1 datetime, IN NumberOfMonth int ) -> BEGIN -> SELECT DATE_ADD(date1, INTERVAL NumberOfMonth MONTH) AS ExtendDate; -> END; -> // Query OK, 0 rows affected (0.20 sec) mysql> DELIMITER ;Now you check whether the stored procedure exists with the help SHOW CREATE command.The query is as follows −mysql> SHOW CREATE PROCEDURE ExtenddatesWithMonthdemo; The following is the output displaying the details of the stored procedure we created above: +--------------------------+--------------------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+ | Procedure | sql_mode ...
Read MoreHow to upgrade MySQL server from command line?
First, you need to open the CMD with the help of shortcut key Windows+R key.After typing cmd, press the OK button. On pressing, you will get a command prompt. The screenshot is as follows −After that, you need to reach the /bin directory. Follow the below instructions. If you are a Windows user, then use the below query to reach the /bin directory.The query is as follows −mysql> select @@datadir;The following is the output displaying the path −+---------------------------------------------+ | @@datadir ...
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