A query plan is a sequence of steps used by a database to access data. Being able to read a query plan is key to understanding the performance of an SQL query. While tuning a query we need to know how the rows are being fetched from the tables? Are the indexes being used? What is the cost of joining to tables? A query plan provides with an answer for all of these questions. [Read More]

In a relational database, the relationships between two tables are defined by foreign keys. Typically, one table has a column that contains the primary key of another table’s row. In JPA, we deal with entity objects that are Java representations of database tables. So we need a different way for establishing relationship between two entities. JPA entity relationships define how these entities refer to each other. For the purpose of this article, I will work with JPA 2. [Read More]