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Articles by Ankith Reddy
Page 73 of 73
ALTER TABLE to add a composite primary key in MySQL?
To add composite primary key, use the ALTER command. Let us first create a demo table The query to create a table. mysql> create table CompositePrimaryKey -> ( -> Id int, -> StudentName varchar(100), -> Age int -> ); Query OK, 0 rows affected (0.56 sec) Haven’t added composite primary key above till now. Let us now check with the help of desc command. mysql> desc CompositePrimaryKey; The following is the output. +-------------+--------------+------+-----+---------+-------+ | Field ...
Read MoreIs it possible to have a function-based index in MySQL?
Function-based index wasn’t possible in MySQL versions below 5.6. Firstly, to create function-based index in MySQL, we will create a table. mysql> create table FunctionIndexDemo - > ( - > FirstName varchar(100) - > ); Query OK, 0 rows affected (0.70 sec) Let us see the syntax to create a function based index. create index index_name on yourTableName (column_name(IntegerSize)); Here is the query. mysql> create index indFirstName on FunctionIndexDemo (FirstName(6)); Query OK, 0 rows affected (0.56 sec) Records: 0 Duplicates: 0 Warnings: 0 ...
Read MoreMySQL's DESCRIBE command?
The MySQL’s DESCRIBE or DESC both are equivalent. The DESC is the short form of DESCRIBE command and used to dipslay the information about a table like column names and constraints on column name. The DESCRIBE command is equivalent to the following command − SHOW columns from yourTableName command. The following is the query that display information about a table with the help of DESCRIBE command. The query is as follows. mysql> DESCRIBE Student; Above, Student is the table name in my database. The above query generates the following output. +-------+--------------+------+-----+---------+-------+ | Field | Type ...
Read MoreHow to create a MySQL table with MyISAM engine table?
To create a MySQL table with MyISAM engine, we can use ENGINE command. Let us first create a table using CREATE command. mysql> create table StudentRecordWithMyISAM -> ( -> Id int, -> StudentName varchar(100), -> StudentAge int -> )ENGINE=MyISAM; Query OK, 0 rows affected (0.26 sec) Above, we have set the ENGINE as “MyISAM”. To check how many columns are present in the table, use DESC command. mysql> DESC StudentRecordWithMyISAM; The following is the output. +-------------+--------------+------+-----+---------+-------+ | Field ...
Read MoreHow to get the size of the tables of a MySQL database?
To get the size of the tables of a MySQL database, you can use the “information_schema.tables”. Here is the syntax to know the size of all tables. SELECT TABLE_NAME AS `ALLTABLESNAME`, ROUND((DATA_LENGTH + INDEX_LENGTH) / 1024 / 1024) AS `TABLESIZEIN(MB)` FROM information_schema.TABLES WHERE TABLE_SCHEMA = "yourDatabaseName" ORDER BY (DATA_LENGTH + INDEX_LENGTH) ASC; Let us apply the above syntax to get the size of the tables. mysql> SELECT TABLE_NAME AS `ALLTABLESNAME`, ROUND((DATA_LENGTH + INDEX_LENGTH) / 1024 / 1024) AS `TABLESIZEIN(MB)` -> FROM information_schema.TABLES WHERE TABLE_SCHEMA = "business" ...
Read MoreWhy doesn't MySQL support millisecond / microsecond precision?
The millisecond/ microsecond precision wasn’t supported in previous versions like 5.6.4. But now MySQL supports millisecond/ microsecond precision with timestamp, datetime, and time. The official statement. “MySQL now supports fractional seconds for TIME, DATETIME, and TIMESTAMP values, with up to microsecond precision”. You can check the MySQL version on your system using the version() method. mysql> SELECT version(); The following is the output. +-----------+ | version() | +-----------+ | 8.0.12 | +-----------+ 1 row in set (0.01 sec) Let us now see the syntax to check the date difference. mysql> SELECT DATEDIFF(now(), ...
Read MoreHow to display current connection info in MySQL?
MySQL provides many functions that give the current connection information. For instance, to know about the current user, use the user() function. Syntax mysql> SELECT CURRENT_USER(); Here is the output that displays the name of the current user. +----------------+ | CURRENT_USER() | +----------------+ | root@% | +----------------+ 1 row in set (0.00 sec) In the above, % tells us about localhost. To check the current connection id, use the following method − mysql> SELECT CONNECTION_ID(); The following is the output that shows the current connection id. ...
Read MoreHow to create boolean column in MySQL with false as default value?
To create a column with ‘false’ as the default value, we can use the concept of “default” at the time of creation of the table. Note − 0 represents false and 1 represents true. Creating a table using “default” false. mysql> create table TrueFalseTable -> ( -> Adult boolean default false -> ); Query OK, 0 rows affected (0.65 sec) Inserting records with no value, since we have set “default” above. mysql> insert into TrueFalseTable values(); Query OK, 1 row affected (0.16 sec) To display records. ...
Read MoreCounters in C#
Counters in C# are performance counters that lets you know about your applications performance. When you will build an application, whether it is a web app, mobile app or even desktop app, you would definitely need to monitor the performance. For performance counters in C#, use the System.Diagnostics.PerformanceCounter class. Set the instance of the PerformanceCounter class and work with the following properties: CategoryName, CounterName, MachineName and ReadOnly. To get the performance categories. var counter = PerformanceCounterCategory.GetCategories(); Now SET performance counters for the category processor. var counter = PerformanceCounterCategory.GetCategories() .FirstOrDefault(category => category.CategoryName == "Processor");
Read MoreDifference between 'struct' and 'typedef struct' in C++?
In C++, there is no difference between 'struct' and 'typedef struct' because, in C++, all struct/union/enum/class declarations act like they are implicitly typedef'ed, as long as the name is not hidden by another declaration with the same name.Though there is one subtle difference that typedefs cannot be forward declared. So for the typedef option, you must include the file containing the typedef before it is used anywhere.
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