Query runs very slow with big tables - sql

Question

Having the following 2 tables:
Table MainProcessed:
Id Value
---------
1 123
2 234
3 112
Table MainAdditionalInfo:
Id MainProcessedId Name Value
--------------------------------------
1 1 'PX' 'px_value'
2 1 'PY' 'py_value'
I need to select all the data from the table MainProcessedId that has some additional info in the table MainAdditionalInfo (at least one record) and it doesn't have a record with the name PX or if it has, this value should be null or empty.
This is what I've tried, but since these tables have a lot of data (more that 100 millions of records, the query is running for a lot of time):
select mp.*
from MainProcessed mp (nolock)
left join MainAdditionalInfo mai1 (nolock) on mp.Id = mai1.MainProcessedId
left join MainAdditionalInfo mai2 (nolock) on mp.Id = mai2.MainProcessedId
where
(mai1.Value is null or mai1.Value = '')
and (mai1.Name = 'PX' or mai1.Name = null)
and mai2.name = 'PY'
Note that the value with the name PX might not be present or can be present with a null or empty value, but the value with the name PY it's always present. Can you suggest me an improving?
Also, I don't have the rights to see the execution plans or to create new objects (indexes).

Answer 1

You could try and phrase your query with exists and not exists:
select p.*
from MainProcessed p
where
exists (
select 1
from MainAdditionalInfo a
where a.MainProcessedId = p.id)
and not exists (
select 1
from MainAdditionalInfo a
where
a.MainProcessedId = p.id
and a.Name = 'PX'
and a.Value <> '' -- null values won't pass that test
)
For performance with this query, you want an index on MainAdditionalInfo(MainProcessedId , Name, Value).

Answer 2

select mp.*
from MainProcessed mp
left join MainAdditionalInfo mai1 on mp.Id = mai1.MainProcessedId and mai2.name ='PX'
where Id in(
select distinct MainProcessedId
from MainAdditionalInfo mai2
inner join MainProcessed on Id = mai2.MainProcessedId and mai2.name ='PY'
)
and (mai1.Value is null or mai1.Value = '')

Answer 3

This is too long for a comment, but I'm expanding on my second one. This doesn't, also, answer the question (there's not enough detail in the question to answer it), but it might help the query planner anyway.
Firstly, you have 2 clauses in you WHERE, like (mai1.Value is null or mai1.Value = '') I assume this is because Value might be NULL if the JOIN fails. If so, don't handle it in your WHERE, put it in the ON.
You also have and mai2.name = 'PY', however, you perform a LEFT JOIN toMainAdditionalInfo mai2. This means the JOIN is now an implicit INNER JOIN. I would, therefore, personally write your query as:
SELECT {List columns, do not use *}
FROM MainProcessed mp
JOIN MainAdditionalInfo mai2 ON mp.Id = mai2.MainProcessedId
LEFT JOIN MainAdditionalInfo mai1 ON mp.Id = mai1.MainProcessedId
AND mai1.Value = ''
AND mai1.Name = 'PX'
WHERE mai2.[name] = 'PY';
I've also removed the NOLOCK hints, as I suspect they do far more harm than good. Bad habits : Putting NOLOCK everywhere

Answer 4

At first, you should ensure that you have FK on MainAdditionalInfo to MainProcessed.ID with index on MainAdditionalInfo.MainProcessedId. Also, you should have an index on MainAdditionalInfo at columns name and value.
Don't use join if you don't need data from MainAdditionalInfo, use exists, for example:
SELECT mp.*
FROM MainProcessed mp (nolock)
WHERE NOT EXISTS (SELECT 1 FROM MainAdditionalInfo mai1
WHERE mai1.Value > ''
AND mai1.Name = 'PX'
AND mp.Id = mai1.MainProcessedId)
AND EXISTS (SELECT 1 FROM MainAdditionalInfo mai2
WHERE mai2.name = 'PY'
AND mp.Id = mai2.MainProcessedId)