Javadoubts

Hibernate Query Language

I always try to write things in such a manner that everyone will be able to read and learn things in one sitting. This article will cover the Hibernate query language from start to finish. In this blog, we will be discussing what HQL is, how it works, and some practical examples.

Hibernate query language is similar to SQL query based or OOPs as query depends on object.

HQL query internally translated by Hibernate into SQL query to performs insert, update, delete and other database operations.

HQL keywords are not case sensitive such as FROM, SELECT, INSERT, DELECT, etc.

FROM

From keyword helps us to read data from specific class. It returns list of objects.

OUTPUT:
John

SELECT

SELECT keyword also helps us to read data from specific table using class name.

keyword SELECT allows us to fetch mentioned column in query. It returns list of objects.

OUTPUT:
John

WHERE

WHERE keyword we can us to refine or filter record.

OUTPUT:
John

ORDER BY

ORDER BY keyword helps us to order records in defined order.

OUTPUT:
Johnnn = 30
Singh = 31
Tarun = 31
Prachi = 31
Nitin = 32
Mengji = 35

GROUP BY

GROUP BY will return unique records for particular condition.

Below example will return unique users of every age. It will return user which exist on first position in table.

OUTPUT:
Johnnn = 30
Singh = 31
Mengji = 35
Nitin = 32

UPDATE

UPDATE keyword helps us to update record using executeUpdate() method. executeUpdate() method return 1 on successful update and 0 on failure.

DELETE

DELETE query will helps us to delete record from table. Below example will delete user having userId 1.

INSERT

INSERT query will helps us to insert record into database.

Aggregate Methods

Please find below some example related to aggregate methods.

We will be using below table as reference to work on aggregate method examples.

query.uniqueResult() will return the Double, Long and int as a query result or output.

avg(): Get average of given input criteria output.

OUTPUT:
Average = 31.5

count(): Get count of given input criteria output.

OUTPUT:
Count = 6

max(): Get maximum value of given input criteria output.

OUTPUT:
Max = 35

min(): Get minimum value of given input criteria output.

OUTPUT:
Min = 30

sum(): Get sum of given input criteria output.

OUTPUT:
Sum = 189