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For our example, let us create a table with NOT NULL constraint. After that, we will modify a column to allow NULL. The following is the query to create a table with NOT NULL constraint. mysql> create table AllowNullDemo -> ( -> id int not null -> ); Query OK, 0 rows affected (0.48 sec)= Insert records with the help of INSERT command. The query is as follows. mysql> insert into AllowNullDemo values(); Query OK, 1 row affected, 1 warning (0.19 sec) mysql> insert into AllowNullDemo values(); ... Read More
Python provides openpyxl module for operating with Excel files. How to create Excel files, how to write, read etc. can be implemented by this module. For installing openpyxl module, we can write this command in command prompt pip install openpyxl If we want to give a sheet title name Example code import openpyxl my_wb = openpyxl.Workbook() my_sheet = my_wb.active my_sheet_title = my_sheet.title print("My sheet title: " + my_sheet_title) Output My sheet title:Sheet To change Title Name Example code import openpyxl my_wb = openpyxl.Workbook() my_sheet = my_wb.active my_sheet.title = "My New Sheet" print("sheet name ... Read More
To convert the MyISAM Engine to InnoDB, we can use the ALTER command. Let us now create a table with the help of engine MyISAM. mysql> create table MyISAMToInnoDBDemo -> ( -> id int, -> Name varchar(100) -> )ENGINE=MyISAM; Query OK, 0 rows affected (0.19 sec) To check if the table is created with engine MyISAM or not. mysql> SELECT TABLE_NAME, ENGINE FROM information_schema.TABLES WHERE TABLE_SCHEMA = 'business' and ENGINE = 'MyISAM'; The following is the output that displays the table created with MyISAM ... Read More
To remove primary key in MySQL, use tje drop primary key command. To understand the concept, let us create a table with column as primary key. mysql> create table PrimaryKeyDemo -> ( -> id int not null, -> Primary key(id) -> ); Query OK, 0 rows affected (0.60 sec) Let us check the description of the table with the help of DESC command. The query is as follows. mysql> desc PrimaryKeyDemo; The following is the output. +-------+---------+------+-----+---------+-------+ | Field | Type ... Read More
C is a general-purpose, high-level language that was originally developed by Dennis M. Ritchie to develop the UNIX operating system at Bell Labs. C was originally first implemented on the DEC PDP-11 computer in 1972. C# is a simple, modern, general-purpose, object-oriented programming language developed by Microsoft within its .NET initiative led by Anders Hejlsberg. The following are the differences between C and C#. Language C language is a structured programming language, whereas C# is an object-orinted language. Memory Management C has manual memory management, whereas memory management is handled automatically in C#. Garbage Collection C do not have ... Read More
ZEROFILL pads the displayed value of the field with zeros up to the display width set in the column definition. Let us understand the role of zero fill in MySQL using an example. Creating a table with two columns, one has zerofill and the second one does not. The query to create a table. mysql> create table ZeroFillDemo -> ( -> First int(18) zerofill, -> Second int(18) -> ); Query OK, 0 rows affected (0.63 sec) We can insert records in the table with the help ... Read More
The debug Lock wait timeout situation occurs because of some threads. If one thread is holding on to some records for a very long time, it means the thread has exceeded time. To see all the details, implement the following query − mysql> SHOW ENGINE INNODB STATUS; The following is the output. +--------+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Type | Name | Status ... Read More
Let us first see how we can display an index from MySQL. For that, use the SHOW command. The query to show an index is as follows − mysql> SHOW INDEX FROM indexingdemo; Here is the output. +--------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | +--------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+ | indexingdemo | 1 | indexName | ... Read More
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 More
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 More