The statement select 1 from any table name means that it returns only 1. For example, If any table has 4 records then it will return 1 four times. Let us see an example. Firstly, we will create a table using the CREATE command. mysql> create table StudentTable -> ( -> id int, -> name varchar(100) -> ); Query OK, 0 rows affected (0.51 sec) Inserting records mysql> insert into StudentTable values(1, 'John'), (2, 'Carol'), (3, 'Smith'), (4, 'Bob'); Query OK, 4 rows affected (0.21 ... Read More

To get a list of MySQL views, we can use the SELECT command with LIKE operator. Let us see the syntax first. mysql> SELECT TABLE_SCHEMA, TABLE_NAME -> FROM information_schema.tables -> WHERE TABLE_TYPE LIKE 'VIEW'; The following is the output that displays the total number of views. +--------------+-----------------------------------------------+ | TABLE_SCHEMA | TABLE_NAME | +--------------+-----------------------------------------------+ | sys ... Read More

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 More

To save MySQL query output into a text file, we can use the OUTFILE command. Let us first create a table. mysql> create table SaveintoTextFile -> ( -> id int, -> name varchar(100) -> ); Query OK, 0 rows affected (0.55 sec) Inserting records into the table. mysql> insert into SaveintoTextFile values(1, 'John'); Query OK, 1 row affected (0.44 sec) mysql> insert into SaveintoTextFile values(101, 'Carol'); Query OK, 1 row affected (0.17 sec) mysql> insert into SaveintoTextFile values(3, 'David'); Query OK, 1 row ... Read More

We can kill the processes with the help of the ‘kill’ command. However, you need to kill those processes one by one, since MySQL does not have any massive kill command. To check how many processes exist, use ‘show processlist’ mysql> show processlist; The following is the output. +----+-----------------+-----------------+------+---------+------+------------------------+------------------+ | Id | User | Host | db | Command | Time | State ... Read More

The following is the syntax to copy a table from one database to another. INSERT INTO yourDestinationDatabaseName.yourTableName SELECT * from yourSourceDatabaseName.yourtableName; Let us see an example. The CREATE command is used to create a table in the database ‘business’. We are creating a new table here. mysql> use business; Database changed mysql> create table OriginalTable -> ( -> id int -> ); Query OK, 0 rows affected (0.46 sec) Creating a new table in the database ‘test’. mysql> use test; Database changed mysql> create ... 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

Triggers in MySQL enable us to describe automatic operations that would be conducted as a result of specific actions happening within tables, such as INSERT, UPDATE, or DELETE. Triggers are very useful to automate repetitive database operations and maintain data integrity. Inserting a Row into Another Table with a Trigger Inserting a row into another table using trigger can be achieved by using the CREATE TRIGGER command followed by the INSERT INTO statement in the trigger's code. This will be capable of adding a row to the second table automatically whenever an action on the first table is performed. ... 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

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