MySQL Rows Not being ignored - mysql

Question

I have the result returning the way I want - I just want to ignore rows where MPG_VALUE > 30 (nvdtechnical.TECH_Value_Float)
But my query returns all - and unwanted rows have NULL in MPG_VALUE column.
How can I return only rows where MPG_VALUE > 30 ?
SELECT *, (SELECT PR_Basic + PR_VAT + PR_Delivery FROM nvdprices
WHERE PR_Id = capder.cder_ID ORDER BY PR_EffectiveTo ASC LIMIT 1) as P11D,
(SELECT nvdtechnical.TECH_Value_Float FROM nvdtechnical
WHERE TECH_TechCode = '11'
AND nvdtechnical.TECH_Id = capder.cder_ID
AND nvdtechnical.TECH_Value_Float > 30
LIMIT 1) as MPG_VALUE
from capmod
JOIN capder ON capder.cder_modcode = capmod.cmod_code
JOIN caprange ON capder.cder_rancode = caprange.cran_code
JOIN capman ON caprange.cran_mantextcode = capman.cman_code
JOIN nvdmodelyear ON capder.cder_ID = MY_Id
AND nvdmodelyear.MY_EffectiveTo = '0000-00-00 00:00:00'
JOIN nvdtechnical ON nvdtechnical.TECH_Id = capder.cder_ID
JOIN nvddictionarytechnical ON nvddictionarytechnical.DT_TechCode = nvdtechnical.TECH_TechCode
JOIN nvddictionarycategory ON nvddictionarycategory.DC_CatCode = nvddictionarytechnical.DT_CatCode
AND nvddictionarycategory.DC_CatCode=4
AND nvddictionarytechnical.DT_TechCode = 67
AND nvdtechnical.TECH_Value_Float >= '255'
JOIN capfueltype ON capfueltype.cft_code = capder.cder_fueltype
JOIN nvdbodystyle ON capmod.cmod_bodystyle = nvdbodystyle.bs_code
WHERE caprange.cran_mantextcode='140'
AND caprange.cran_code='522'
AND capder.cder_fueltype='P'
AND capder.cder_transmission='A'
AND nvdbodystyle.bs_code='3'
AND (cmod_discontinued=0 OR cmod_discontinued=2015)
AND capman.cman_code IN ('1','140','164')
AND caprange.cran_code IN ('924','126','147','955','965','661')
ORDER BY P11D, capman.cman_name ASC, caprange.cran_name, capmod.cmod_name

Answer 1

That is because you are doing a scalar query for the MPG Value. You are not really filtering which rows to show or hide, rather, you are showing all rows that has a value matched from your main query.
Imagine a left join, that is like what you are doing
SELECT nvdtechnical.TECH_Value_Float FROM nvdtechnical
WHERE TECH_TechCode = '11'
AND nvdtechnical.TECH_Id = capder.cder_ID
**AND nvdtechnical.TECH_Value_Float > 30**
LIMIT 1
to properly filter the data, you must filter in once more outside it in your where condition:
the easiest way would be like this one.
SELECT *
FROM (
SELECT *, (SELECT PR_Basic + PR_VAT + PR_Delivery FROM nvdprices
WHERE PR_Id = capder.cder_ID ORDER BY PR_EffectiveTo ASC LIMIT 1) as P11D,
(SELECT nvdtechnical.TECH_Value_Float FROM nvdtechnical
WHERE TECH_TechCode = '11'
AND nvdtechnical.TECH_Id = capder.cder_ID
AND nvdtechnical.TECH_Value_Float > 30
LIMIT 1) as **MPG_VALUE**
from capmod
JOIN capder ON capder.cder_modcode = capmod.cmod_code
JOIN caprange ON capder.cder_rancode = caprange.cran_code
JOIN capman ON caprange.cran_mantextcode = capman.cman_code
JOIN nvdmodelyear ON capder.cder_ID = MY_Id
AND nvdmodelyear.MY_EffectiveTo = '0000-00-00 00:00:00'
JOIN nvdtechnical ON nvdtechnical.TECH_Id = capder.cder_ID
JOIN nvddictionarytechnical ON nvddictionarytechnical.DT_TechCode = nvdtechnical.TECH_TechCode
JOIN nvddictionarycategory ON nvddictionarycategory.DC_CatCode = nvddictionarytechnical.DT_CatCode
AND nvddictionarycategory.DC_CatCode=4
AND nvddictionarytechnical.DT_TechCode = 67
AND nvdtechnical.TECH_Value_Float >= '255'
JOIN capfueltype ON capfueltype.cft_code = capder.cder_fueltype
JOIN nvdbodystyle ON capmod.cmod_bodystyle = nvdbodystyle.bs_code
WHERE caprange.cran_mantextcode='140'
AND caprange.cran_code='522'
AND capder.cder_fueltype='P'
AND capder.cder_transmission='A'
AND nvdbodystyle.bs_code='3'
AND (cmod_discontinued=0 OR cmod_discontinued=2015)
AND capman.cman_code IN ('1','140','164')
AND caprange.cran_code IN ('924','126','147','955','965','661')
ORDER BY P11D, capman.cman_name ASC, caprange.cran_name, capmod.cmod_name
) x
WHERE x.MPG_VALUE IS NOT NULL;
Note that the x.MPG_VALUE which is filtered outside is your scalar query.
Edit: You can try other methods like, inner join.
SELECT *, (SELECT PR_Basic + PR_VAT + PR_Delivery FROM nvdprices
WHERE PR_Id = capder.cder_ID ORDER BY PR_EffectiveTo ASC LIMIT 1) as P11D,
MPG_VALUE.TECH_Id
from capmod
JOIN capder ON capder.cder_modcode = capmod.cmod_code
JOIN caprange ON capder.cder_rancode = caprange.cran_code
JOIN capman ON caprange.cran_mantextcode = capman.cman_code
JOIN nvdmodelyear ON capder.cder_ID = MY_Id
AND nvdmodelyear.MY_EffectiveTo = '0000-00-00 00:00:00'
JOIN nvdtechnical ON nvdtechnical.TECH_Id = capder.cder_ID
JOIN nvddictionarytechnical ON nvddictionarytechnical.DT_TechCode = nvdtechnical.TECH_TechCode
JOIN nvddictionarycategory ON nvddictionarycategory.DC_CatCode = nvddictionarytechnical.DT_CatCode
AND nvddictionarycategory.DC_CatCode=4
AND nvddictionarytechnical.DT_TechCode = 67
AND nvdtechnical.TECH_Value_Float >= '255'
JOIN capfueltype ON capfueltype.cft_code = capder.cder_fueltype
JOIN nvdbodystyle ON capmod.cmod_bodystyle = nvdbodystyle.bs_code
INNER JOIN
(
SELECT TECH_Value_Float,TECH_Id
FROM nvdtechnical
WHERE TECH_TechCode = '11'
AND TECH_Value_Float > 30
) MPG_VALUE
ON MPG_VALUE.TECH_Id = capder.cder_ID
WHERE caprange.cran_mantextcode='140'
AND caprange.cran_code='522'
AND capder.cder_fueltype='P'
AND capder.cder_transmission='A'
AND nvdbodystyle.bs_code='3'
AND (cmod_discontinued=0 OR cmod_discontinued=2015)
AND capman.cman_code IN ('1','140','164')
AND caprange.cran_code IN ('924','126','147','955','965','661')
ORDER BY P11D, capman.cman_name ASC, caprange.cran_name, capmod.cmod_name;