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Articles by Chandu yadav
Page 80 of 81
How to raise an error within MySQL?
MySQL has introduced signals similar to an exception in other languages. Let us first see the syntax of signal. SIGNAL SQLSTATE ' PredefinedValueforSignalError' SET MESSAGE_TEXT = 'AnyMessageInformation'; Above, we have set our own error message text as well. We will apply the above query to get an error message with the help of signals. mysql > SIGNAL SQLSTATE '42927' SET MESSAGE_TEXT = 'Error Generated'; The following is the output of the above query. ERROR 1644 (42927): Error Generated In the above output, ‘42927’ is a SQLSTATE and ‘Error Generated’ is an error message, which we added.
Read MoreMySQL ON vs USING?
In general, we use ON in MySQL. In Joins, we use ON in a set of columns. USING is useful when both the tables share a column of the exact same name on which they join. Example of On. Creating our first table. mysql> CREATE table ForeignTableDemo -> ( -> Id int, -> Name varchar(100), - > FK int - > ); Query OK, 0 rows affected (0.47 sec) Creating our second table. mysql> CREATE table PrimaryTableDemo - > ...
Read MoreWhat is the MySQL JDBC driver connection string?
The MySQL JDBC connection string look like this − Class.forName("com.mysql.jdbc.Driver"); Above, Driver is an interface. Whenever your JDBC is running outside an application server, then the class DriverManager establish the connection. The DriverManager class is as follows − conn = (Connection) DriverManager.getConnection("jdbc:mysql://localhost/yourdatabaseName",”yourRootName","yourPassword"); Now, I am applying the above connection string to connect Java to MySQL database. The code is as follows. The following is the output that shows that MySQL connection with Java is successful.
Read MoreCount the number of occurrences of a string in a VARCHAR field in MySQL?
To count the number of occurrences of a string in a VARCHAR, we can use the logic of subtraction with length. First, we will create a table with the help of create command. mysql> create table StringOccurrenceDemo -> ( -> Cases varchar(100), -> StringValue varchar(500) -> ); Query OK, 0 rows affected (0.56 sec) After executing the above table, we will insert records into the table. The query is as follows − mysql> insert into StringOccurrenceDemo values('First', 'This is MySQL Demo and MySQL is ...
Read MoreHow to use a function for default value in MySQL?
We cannot use a function for default value in MySQL, but we can use triggers. Let us see an example. First, we will create a table. The CREATE command is used to create a table. mysql> CREATE table TbLFunctionTrigger - > ( - > id int, - > username varchar(100) - > ); Query OK, 0 rows affected (0.55 sec) The following is the syntax to create a trigger and include a default value. CREATE TRIGGER anyName BEFORE INSERT ON yourTableName FOR EACH ROW ...
Read MoreDifference between two timestamps in seconds in MySQL?
Let us now see the following methods to calculate the time difference between two timestamps in seconds. Method The following is the query to calculate the difference between two timestamps. mysql> SELECT TIMESTAMPDIFF(SECOND, '2018-10-17 11:51:55', '2018-10-17 11:51:58'); The following is the output in seconds. +---------------------------------------------------------------------+ | TIMESTAMPDIFF(SECOND, '2018-10-17 11:51:55', '2018-10-17 11:51:58') | +---------------------------------------------------------------------+ | ...
Read MoreRank function in MySQL?
The rank() function can be used to give a rank for every row within the partition of a result set. First, let us create a table − mysql> create table RankDemo mysql> ( mysql> id int mysql> ); Query OK, 0 rows affected (0.53 sec) Inserting records into table. mysql> insert into RankDemo values(1); Query OK, 1 row affected (0.19 sec) mysql> insert into RankDemo values(3); Query OK, 1 row affected (0.12 sec) mysql> insert into RankDemo values(3); Query OK, 1 row affected (0.11 ...
Read MoreHow to do a batch insert in MySQL?
To do a batch insert, we need to use all column names with parenthesis, separated by ‘, ’. Let us see an example. First, we will create a table. The following is the CREATE command to create a table. mysql> CREATE table MultipleRecordWithValues - > ( - > id int, - > name varchar(100) - > ); Query OK, 0 rows affected (0.88 sec) The following is the syntax of batch insert. INSERT into yourTableName values(column1, column2, ....N), (column1, column2, ....N), (column1, column2, ....N), ...........N; ...
Read MoreOpen MySQL root access from all hosts?
To open root access from all hosts, we need to change the database to “mysql” with the help of USE command. The syntax of USE command is as follows − USE anyDatabasename; Now, I will use predefined database ‘mysql’, which is as follows − mysql> use mysql; Database changed I have changed the database above. Here is the query to get root access from the entire host − mysql> UPDATE user set host='%' where host='localhost'; Query OK, 6 rows affected (0.19 sec) Rows matched: 6 Changed: 6 Warnings: 0
Read MoreHow to get the count of each distinct value in a column in MySQL?
Let us see an example to get the count of each distinct value in a column. Firstly, we will create a table. The CREATE command is used to create a table. mysql> create table DistinctDemo1 - > ( - > id int, - > name varchar(100) - > ); Query OK, 0 rows affected (0.43 sec) Inserting records mysql> insert into DistinctDemo1 values(1, 'John'); Query OK, 1 row affected (0.34 sec) mysql> insert into DistinctDemo1 values(2, 'John'); Query OK, 1 row affected (0.20 sec) ...
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