DbVisualizer is a very popular GUI application to view the data stored on a database. It supports various databases such as Oracle, MySQL etc. It relies on different database drivers to connect to the database server and access the data stored there. In this post, we will try to solve one problem when accessing the latest MySQL database(8.0+) through DbVisualizer. MySQL database starting from 8.0 has lots of changes which may not be compatible with old version of software or libraries which interact with it. There are also lots of issues reported while accessing the 8.0+ version of MySQL ...

There are two ways to install Oracle database on Linux :1). Using GUI; 2). Using response file. In this post, the method for using response file will be introduced.To install Oracle, please first get the Oracle database installation file ready. It can be downloaded from Oracle OTN. You need to have an Oracle account before you can download them.And there are three major components of the Oracle database installation : 1). The installation itself; 2). The network configuration; 3). Database creation. Each of the component can be completed with a response file. There are sample response files in...

Oracle database is the most popular database system among enterprises. To start working on Oracle database, some concepts must be understood first. They include database, instance, schema and user etc. And among these concepts, some have different meanings from those in other database systems such as MS SQL, MySQL, DB2.On the web, there are already some good posts which explain different concepts such as Ask Tom's database vs instances, Difference between database vs user vs schema. In this post, these concepts with be summarized based on real application development experience.Database : A co...

Oracle database is now a mature and popular RDBMS which is used by lots of enterprises. With its evolution, many utilities and applications are developed around it as well. Now Oracle database also provides cloud support. As a DBA, managing Oracle database is daily routine work and some tools may be used frequently. One of them is sqlplus, the command line tool for executing SQL command.sqlplus is installed while the Oracle database is installed. To start sqlplus, one just needs to open a terminal and then type sqlplus. Then it will connect to the default schema and will prompt you to enter th...

When doing website development with MySQL, we often need to do database backup and restore. For website, the data in database will grow quickly, so when we back up the database, the size of the generated sql file may be over 80MB which is the max allowed size when we want to import a sql file for restoring our database using phpMyAdmin. To workaround this limit, we need to review the documentation of phpMyAdmin. Fortunately, I found an online article written by David Pratt  which gave us a very simple solution to this problem.Find the config.inc.php file located in the phpmyadmin director...

Have you ever seen "<=>" in a SQL query while using MySQL? Does it mean less and equals to and greater than? Actually if you consider it as the union of <= and =>, great, you are close to it. This is one form of equal operator in MySQL, it has the similar meaning to the = operator with some subtle difference.According to MySQL documentation, <=> is NULL-safe equal. This operator performs an equality comparison like the = operator, but returns 1 rather than NULL if both operands are NULL, and 0 rather than NULL if one operand is NULL.For example:mysql> SELECT 1 <=> 1,...

When working with Hibernate and MySQL, sometimes some exceptions will be thrown after sometime. The exception may seem like :java.sql.SQLException: Data source rejected establishment of connection, message from server: "Too many connections"This means there are too many active connections on the MySQL, you can useSHOW STATUS LIKE '%Threads_connected%';to check the active connections to MySQL. If you want to change the maximum connections allowed to MySQL. You can execute:set global max_connections = [num];You may forget to manually call session.close() methods iin your codes. If you have done ...

After installing MySQL, when we try to start MySQL, sometimes we may not be able to start it. The reasons can be different. We share some general cases where MySQL cannot be started.Case 1: Directory or file permission issueIf the permission is set wrongly in MySQL's $datadir and its sub directories or files, MySQL will not be able to read and write files normally.Error message:mysqld_safe Starting mysqld daemon with databases from /usr/local/mysql/data/usr/local/mysql/bin/mysqld_safe: line 107: /usr/local/mysql/data/imysql.local.err: Permission deniedCase 2: Port conflictThere may be other my...