Dynamic MySQL Where Clause in Stored Procedure - mysql

Question

I have a question and maybe its simple (for you Gurus).
I'm transposing my SQL Paging class from C# to a MySQL Stored Procedure. In my C# home-made object, the query is dynamically built based off a criteria. Example:
if(keywords is not null)
{
whereClause += "WHERE description LIKE '%keywords%'"
}
if(price is not null)
{
whereClause += "AND price = '%price%'"
}
....
string query = "SELECT col1, col2 FROM tblThreads " + whereClause
Now, my question is: How do I do a dynamic where clause in MySQL similar to this? Or rather, if they don't enter anything for those parameters, how would I tell MySQL in the Stored Procedure to skip those? IE:
SELECT col1, col2 FROM tblThreads
Would something like this work, if those parameters were null?
SELECT col1, col2 FROM tblThreads WHERE (IS NULL #keywords OR description like '%#keywords%'
??
Thanks guys.

Answer 1

You can use CASE statement to check for the value of #keywords, eg.
SELECT col1, col2
FROM tblThreads
WHERE description LIKE CASE WHEN #keywords IS NULL
THEN description
ELSE CONCAT('%', #keywords, '%')
END
AND
price LIKE CASE WHEN #price IS NULL
THEN price
ELSE CONCAT('%', #price, '%')
END

Answer 2

The easiest way if you're allowing them to query the entire database is to just add a 1 = 1 to your statement Something like
whereClause = "WHERE 1 = 1"
if(keywords is not null)
{
whereClause += "AND description LIKE '%keywords%'"
}
if(price is not null)
{
whereClause += "AND price = '%price%'"
}

Answer 3

SELECT col1, col2
FROM tblThreads
WHERE case when #keywords is not null then description like '%' + #keywords + '%' when #price is not null then price like'%' + #price + '%' end

Answer 4

DELIMITER $$
CREATE DEFINER=`root`#`localhost` PROCEDURE `sp_Name4`(
IN a int(255),
IN b int(255),
IN dept_id_in int(255)
)
BEGIN
SELECT
emp.emp_id, emp.emp_name,
emp.emp_job,
emp.dept,
emp.percent_doctor,
emp.percent_center,
patient_exam.exam_id,
patient_exam.p_id,
ABS(SUM(patient_exam.exam_price)) as SUM_price,
ABS((SUM(patient_exam.exam_price)* emp.percent_center )/100 ) as total_doc,
ABS((SUM(patient_exam.exam_price)* emp.percent_doctor )/100 ) as total_center
FROM emp
left join patient_exam
ON emp.emp_id = patient_exam.doctor
WHERE emp.emp_is_delete=0 and patient_exam.ex_is_delete=0 and 1=1
CASE WHEN dept_id_in IS not NULL
THEN
and patient_exam.dept_id=dept_id_in
END
group by emp.emp_id, patient_exam.exam_id order by emp.emp_id, patient_exam.exam_id desc limit a,b;
END$$
DELIMITER ;