Thursday, 5 January 2012

Pass multiple parameters, dynamic query in Pure SQL in Database Adapter

I came across a case in which I was required to pass the bind parameters values on the fly. The values of parameters were not fixed and hence I couldn't define all of them as the bind parameters. Hence in the search of the solution I wasted considerable time until I was directed to see this great solution. The solution was fantastic and I customized it further to make it work with SOA Suite11g. This can be further extended with Joins to do wonders as required. 


Use Case : I want the salaries of all the employees whose first names I'd pass at run time. Hence it can be single name or n names coming as parameters. The very simple query, as it comes to our mind, would be


SELECT SALARY FROM EMPLOYEES WHERE F_NAME IN (?) 
Where ? is the argument that is passed dynamically. 


However, the same query doesn't work in DB adapter for any combination passed dynamically such as ('NEERAJ', 'JACOB') or "('NEERAJ', 'JACOB')" or 'NEERAJ', 'JACOB' for the adapter tries to interpret the incoming argument as a bind parameter and not SQL string.


Solution :  If the parameters can be passed as a result of an inner query the problem can be solved. The following query uses CONNECT BY LEVEL clause to separate the individual parameter values separated by a and represents them as individual result row.



SELECT SALARY FROM EMPLOYEES WHERE F_NAME 
IN (WITH BIND_PARAM_LIST AS
(SELECT #val FROM dual)
SELECT SUBSTR(#val1, (decode(LEVEL, 1, 0, instr(#val2, ':', 1, LEVEL -1)) + 1), (decode(instr(#val3, ':', 1, LEVEL) -1, -1, LENGTH(#val4), instr(#val5, ':', 1, LEVEL) -1)) -(decode(LEVEL, 1, 0, instr(#val6, ':', 1, LEVEL -1)) + 1) + 1) a
FROM 
BIND_PARAM_LIST CONNECT BY LEVEL <=
(SELECT(LENGTH(#val7) -LENGTH(REPLACE(#val8, ':', NULL)))
FROM 
BIND_PARAM_LIST) + 1)


To understand the query one needs to be familiar with the CONNECT BY clause which is used for hierarchical queries. If you simply do 


SELECT LEVEL FROM DUAL CONNECT BY LEVEL <=5, it prints 1 to 5 in each row like

LEVEL
=====
1
2
3
4
5


The same logic is being used in the above query to separate the various F_Names. It just sub-strings the incoming string NEERAJ:JACOB:ROBERT, wise for each LEVEL to feed the result in the IN clause as 


NEERAJ
JACOB
ROBERT


Usage : Just add this query in the DB Adapter. Be careful to use # instead of ? as in 11g the bind variable name can be defined as #bind_variable, in our case #val1, #val2 ... #val8. Also you'll have to assign the same input string to these multiple vals. The val variables get exposed as input parameters while assigning and can be assigned as 'NEERAJ:JACOB:ROBERT'(your parameter list). You can use any other separator too e.g. ; instead of : by customizing the query a bit. 


Just deploy the project and it is done. The same thing can also be achieved by using query-database() function as described here.

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