To find the port of the MySQL server, the command show can be used. Its syntax is as follows −show variables where variable_name=’port’;The above syntax is used to get the port number of the MySQL server using the following query −mysql> show variables where variable_name = 'port';After executing the above command, port of MySQL server is obtained as 3306. This can be seen in the following output −+---------------+-------+ | Variable_name | Value | +---------------+-------+ | port          | 3306  | +---------------+-------+ 1 row in set (0.01 sec)Alternatively, the system variable @@port can also be used to find ... Read More

The MySQL version before 5.0.3 was capable of storing 255 characters but from the version 5.0.3 , it is capable of storing 65, 535 characters.MySQL official documentation states −The effective maximum length of a VARCHAR in MySQL 5.0.3 and later is subject to the maximum row size (65, 535 bytes, which is shared among all columns) and the character set used. For example, utf8 characters can require up to three bytes per character, so a VARCHAR column that uses the utf8 character set can be declared to be a maximum of 21, 844 characters. Keep in mind that the limitation of ... Read More

We can store the money values in MySQL in decimal(value1, value2). Here, value1 is the total range including value2. The value2 specifies the number of digits after the decimal point. To understand this concept, the steps are given below.First a table is created using the create command.mysql> CREATE table MoneyDemo -> ( -> Id int, -> Money decimal(10, 2) -> ); Query OK, 0 rows affected (0.46 sec)As can be seen from the above command, the decimal value has 10 digits only and also 2 digits only after the decimal point.After creating the table, some records are inserted with the ... Read More

In MySQL “Where 1=1” results in all the rows of a table as this statement is always true. An example to better unerstand this statement is given as follows −First, a table is created with the help of the create command. This is given as follows −mysql> CREATE table WhereConditon -> ( -> id int, -> name varchar(100) -> ); Query OK, 0 rows affected (0.43 sec)After successfully creating a table, some records are inserted with the help of insert command The query for this is given as follows −mysql> INSERT into WhereConditon values(1, 'John'); Query OK, 1 row affected ... Read More

The max_allowed_packet size is a session variable and is also a read only variable.To check what is the present value of max_allowed_packet, the command show variables is used. It is given as follows −mysql> show variables like 'max_allowed_packet';The following is the output+--------------------+---------+ | Variable_name | Value | +--------------------+---------+ | max_allowed_packet | 4194304 | +--------------------+---------+ 1 row in set (0.04 sec)The value of the max_allowed_packet can be changed in the ‘my.ini’ file on the client side. The query for that is given as follows −max_allowed_packet = 4567890; Now, the value can be changed globally ... Read More

To update a column value, the update command as well as the replace method can be used. The steps to better understand these are given as follows −First create a table with the help of the create command. This is given as follows −mysql> CREATE table DemoOnReplace -> ( -> Id int, -> Name varchar(200) -> ); Query OK, 0 rows affected (0.63 sec)After successfully creating a table, some records are inserted with the help of the insert command. This is shown below −mysql> INSERT into DemoOnReplace values(1, 'John'); Query OK, 1 row affected (0.10 sec) mysql> INSERT into ... Read More

To see all the foreign keys to a table or column, the referenced_column_name command is used.First, two tables are created and then related with the help of the foreign key constraint.Creating the first table −mysql> CREATE table ForeignTable -> ( -> id int, -> name varchar(200), -> Fk_pk int -> ); Query OK, 0 rows affected (0.43 sec)After creating the first table successfully, the second table is created as follows −mysql> CREATE table primaryTable1 -> ( -> Fk_pk int, -> DeptName varchar(200), -> Primary key(Fk_pk) -> ); Query OK, 0 rows affected (0.48 sec)Now, both the tables are related with ... Read More

The auto_increment is a default property that automatically increments the newly added record by 1. The auto_increment can be changed from the beginning as well. The procedure for that is given below −First, a table is created.mysql> CREATE table DemoAuto -> ( -> id int auto_increment, -> name varchar(100), -> primary key(id) -> ); Query OK, 0 rows affected (0.47 sec)After that the alter table command is used to change the starting number of auto_incremnt which starts from 1 by default. The starting value is changed to 100.mysql> alter table DemoAuto auto_increment = 100; Query OK, 0 rows affected (0.24 ... Read More

The schema_name command is used to check if a MySQL database exists or not. The syntax of this command is as follows −select schema_name from information_schema.schemata where schema_name = 'database name';Now, the above command is used to check whether the database exists or not. The query for that is as follows −Case 1 − The database exists.mysql> select schema_name from information_schema.schemata where schema_name = 'business'; The output obtained is as follows −+-------------+ | SCHEMA_NAME | +-------------+ | business | +-------------+ 1 row in set (0.00 sec)Case 2 − The database does not exist.mysql> select schema_name from information_schema.schemata ... Read More

To understand error 1452, first we need to create a table and relate that to another table with the help of a foreign key constraint.Creating the first table −mysql> CREATE table ForeignTable -> ( -> id int, -> name varchar(200), -> Fk_pk int -> ); Query OK, 0 rows affected (0.43 sec)After creating the first table successfully, we will create the second table −mysql> CREATE table primaryTable1 -> ( -> Fk_pk int, -> DeptName varchar(200), -> Primary key(Fk_pk) -> ); Query OK, 0 rows affected (0.48 sec)Now, we have created both tables. Then both the tables are related with the ... Read More