Posts tagged: sql
Once again a short reminder how to aggregate SQL statement execution results as a single XML CLOB in Oracle.
Assume there is an Oracle table containing user data:
create table t_user( user_id number(15) not null, user_name varchar2(100) not null, role varchar2(100) not null, email varchar2(100) ) /
Now aggregating all the user entries as single XML CLOB can be done using following statement:
select xmlelement("users",
xmlagg(xmlelement("user",
xmlattributes( t.user_id as "id",
t.user_name as "name",
t.role,
t.email
)
))
).getclobval() xml
from t_user t
This will result in a CLOB that looks like this:
<users> <user id="1" name="foo" role="USER" email="[email protected]"></user> <user id="2" name="bar" role="ADMIN" email="[email protected]"></user> ... <user id="999" name="xyz" role="USER" email="[email protected]"></user> </users>
MyBatis is a data mapping framework providing capabilities to map SQL statements to Java Objects using Annotations or XML.
(Typical) Mapping rules can be written by hand or automatically generated by MyBatis Generator.
MyBatis Generator will generate:
Furthermore it is possible to write custom plugins to enhance the generation process and to provide additional capabilities to generated sources.
Several months ago i’ve written some MyBatis Generator Plugins presented in this post. Check out the project’s source code on GitHub: https://github.com/bigpuritz/mybatis-generator-plugins
This SQL statement will return n-th maximum row from the table:
select distinct a.myColumn from myTable a where &n = ( select count(distinct(b.myColumn)) from myTable b where a.myColumn <= b.myColumn)
where &n is a max. row number to return.
For example this statement will return an employee with the second best salary:
select distinct a.name, a.salary
from employee a
where 2 = (select count(distinct(b.salary))
from employee b
where a.salary <= b.employee.salary)