Given a database with two tables X and Y, I have a query that should LEFT JOIN the two tables on attributes X.a1 and Y.b1. I used the following query:
SELECT X.a1, X.a2, Y.b1, Y.b2 FROM X LEFT JOIN Y ON (X.a1 = Y.b1)
I thought that would be good enough to work, even if Y is currently an empty table. However, the query breaks because table Y is empty, it seems. Is there any way to reformat this query so that even if Y is an empty table, the LEFT JOIN will not break? Or do I just need to always make sure that there is some data in table Y, even if it doesn't match anything in table X (hence the LEFT JOIN).
Since you didn't post your actual SQL, i just make assumption here. My experience telling me that you might have a where clause that causes the SQL to return empty set.
SELECT X.a1, X.a2, Y.b1, Y.b2 FROM X LEFT JOIN Y ON (X.a1 = Y.b1)
WHERE Y.b3 = 'something'
The above SQL will return empty result set. You may need to modify your SQL into the following format, by bring up the problematic where clause to LEFT JOIN ON clause.
SELECT X.a1, X.a2, Y.b1, Y.b2 FROM X
LEFT JOIN Y ON (X.a1 = Y.b1 and Y.b3 = 'something')
Your table names are a little confusing. Is it X and Y, or X.a and Y.b?
If X and Y:
SELECT X.a1, X.a2, Y.a1, Y.b2 FROM X LEFT OUTER JOIN Y ON (X.a1 = Y.b1)
should bring back all X, with nulls for the Y.a1 and Y.b2 where there is no matching record.
Try your query on some Sql editor that returns errors like
HeidiSQL or similar. In my case the problem was ambiguous id in WHERE clause.
Related
I want to join three tables together in order to find a value of the third table's id. The SQL statement works correctly, and looks like this:
SELECT table_three.id from table three
JOIN (table_one JOIN table_two ON table_one.id = table_two.table_one_id)
ON table_three.table_two_id = table_two.id
WHERE table_one.id = x AND table_two.external_id = y AND table three.external_id = z
What would the SQL Alchemy code look like for something like this? I have looked at the documentation, but their query is different than mine, and I can't make sense of the example well enough to apply it to my own code.
Turns out that chaining join statements does exactly what we needed all along.
result = connection.execute(
select(Table_three.id)
.join(Table_two, Table_three.Table_two_id == Table_two.id)
.join(Table_one, Table_two.Table_one_id == Table_one.id)
.where(
and_(
Table_three.external_id == z,
Table_two.external_id == y,
Table_on.id = x
)
)
).one_or_none()
I have two tables named DE1_0_2008_TO_2010_OUTPATIENT_CLAIMS_SAMPLE_1 and DE1_0_2008_BENEFICIARY_SUMMARY_FILE_SAMPLE_1 in the same database.
I have to perform a query on DE1_0_2008_TO_2010_OUTPATIENT_CLAIMS_SAMPLE_1 and then perform the LEFT JOIN of this queried result with `DE1_0_2008_BENEFICIARY_SUMMARY_FILE_SAMPLE_1'. The query alone results in 1178 rows which is fine. But I am not able to do the LEFT JOIN. I used this SQL query:
SELECT *
FROM `DE1_0_2008_TO_2010_OUTPATIENT_CLAIMS_SAMPLE_1`
LEFT JOIN DE1_0_2008_BENEFICIARY_SUMMARY_FILE_SAMPLE_1
ON DE1_0_2008_TO_2010_OUTPATIENT_CLAIMS_SAMPLE_1.DESYNPUF_ID = DE1_0_2008_BENEFICIARY_SUMMARY_FILE_SAMPLE_1.DESYNPUF_ID
WHERE DE1_0_2008_TO_2010_OUTPATIENT_CLAIMS_SAMPLE_1.ICD9_DGNS_CD_1 = 7243 OR DE1_0_2008_TO_2010_OUTPATIENT_CLAIMS_SAMPLE_1.ICD9_DGNS_CD_2 = 7243 OR DE1_0_2008_TO_2010_OUTPATIENT_CLAIMS_SAMPLE_1.ICD9_DGNS_CD_3 = 7243 OR ICD9_DGNS_CD_4 = 7243
This query is technically fine.
Note that it can be rewritten more elegantly as follows, but really you need to take a closer look at both partitioning and, crucially, normalisation...
SELECT *
FROM DE1_0_2008_TO_2010_OUTPATIENT_CLAIMS_SAMPLE_1 o
LEFT
JOIN DE1_0_2008_BENEFICIARY_SUMMARY_FILE_SAMPLE_1 b
ON o.DESYNPUF_ID = b.DESYNPUF_ID
WHERE 7243 IN(o.ICD9_DGNS_CD_1,o.ICD9_DGNS_CD_2,o.ICD9_DGNS_CD_3,o.ICD9_DGNS_CD_4);
I'm working with a large stored procedure, I'm having trouble with a small portion of it.
When I execute a query on the table im joining, there can be 0, 1 or 2 results. If there are 0 results, I don't really care, my code returns null values, no big deal. If there is 1 result, my code returns the correct values, however, if there are 2 results, I am having trouble selecting the second result.
My code below works until the second OutterApply(the AHM2 stuff). Does anyone see what I am doing wrong?
The animal ID is identical for both OuterApplys. I just need to return the second result, if there is one, and if it is not the same as the first one.
SELECT TOP 1
AHM.AnimalHerdManagementId,
AHM.HerdManagementId,
AHM2.AnimalHerdManagementId,
AHM2.HerdManagementId,
HM.Code AS HerdManagementCode,
HM2.Code AS HerdManagementCode2
OUTER APPLY
(
SELECT TOP 1 AHM.AnimalHerdManagementId, AHM.HerdManagementId
FROM dbo.AnimalHerdManagement AHM
WHERE AHM.AnimalId = A.AnimalId AND ISNULL(AHM.EffectiveFrom, #EffectiveFrom) <= #EffectiveFrom
ORDER BY AHM.EffectiveFrom DESC
) AHM
LEFT JOIN dbo.HerdManagement HM ON AHM.HerdManagementId = HM.HerdManagementId
OUTER APPLY
(
SELECT TOP 1 AHM2.AnimalHerdManagementId, AHM2.HerdManagementId
FROM dbo.AnimalHerdManagement AHM2
WHERE AHM2.AnimalId = A.AnimalId AND AHM2.AnimalHerdManagementId != AHM.AnimalHerdManagementId AND ISNULL(AHM2.EffectiveFrom, #EffectiveFrom) <= #EffectiveFrom
ORDER BY AHM2.EffectiveFrom DESC
) AHM2
LEFT JOIN dbo.HerdManagement HM2 ON AHM2.HerdManagementId = HM2.HerdManagementId
I think I can help you with the OUTER APPLY but the method of getting the two different values is going to need some help as my solution is a total hack.
First, you don't need to join on the outer apply. The join is implied. So you can completely eliminate the join syntax from your query.
Second, AnimalHerdManagement looks/seems like a special table called a Junction Table. All the data contained in it is contained elsewhere (That it contains completely redundant data is why it's called a special table). But that is minor.
Finally, here is some example code I threw together that accomplishes what you are after. The method I am using to retrieve different results on the two outer apply's is a hack, but if you are sure that will always be true, it might work. I am not able to get a multi-level outer apply to work.
select * from AH_Animal A
outer apply
(
select max (HerdManagementID) as HerdMgmtID1 from AH_AnimalHerdManagement HM1 where HM1.AnimalID = A.AnimalID
) as z
outer apply
(
select min (HerdManagementID) as HerdMgmtID2 from AH_AnimalHerdManagement HM2 where HM2.AnimalID = A.AnimalID
) as zz
I hope that helped. There has to be another solution to this, as this would not work at all if you ever expected 3 results.
Query Results:
I have a query as follows
select
Sum(If(departments.vat, If(weeklytransactions.weekendingdate Between
'2011-01-04' And '2099-12-31', weeklytransactions.takings / 1.2,
If(weeklytransactions.weekendingdate Between '2008-11-30' And '2010-01-01',
weeklytransactions.takings / 1.15, weeklytransactions.takings / 1.175)),
weeklytransactions.takings)) As Total,
weeklytransactions.weekendingdate,......
and another that returns a vat rate as follows
select format(Max(Distinct vat_rates.Vat_Rate),3) From vat_rates Where
vat_rates.Vat_From <= '2011-01-03'
I want to replace the hard coded if statement with the lower query, replacing the date in the lower query with weeklytransactions.weekendingdate.
After Kevin's comments, here is the full query I'm trying to get to work;
Select Max(vat_rates.vat_rate) As r,
If(departments.vat, weeklytransactions.takings / r, weeklytransactions.takings) As Total,
weeklytransactions.weekendingdate,
Week(weeklytransactions.weekendingdate),
round(datediff(weekendingdate, (if(month(weekendingdate)>5,concat(year(weekendingdate),'-06-01'),concat(year(weekendingdate)-1,'-06-01'))))/7,0)+1 as fyweek,
cast((Case When Month(weeklytransactions.weekendingdate) >5 Then Concat(Year(weeklytransactions.weekendingdate), '-',Year(weeklytransactions.weekendingdate) + 1) Else Concat(Year(weeklytransactions.weekendingdate) - 1, '-',Year(weeklytransactions.weekendingdate)) End) as char) As fy,
business_units.business_unit
From departments Inner Join (business_units Inner Join weeklytransactions On business_units.buID = weeklytransactions.businessUnit) On departments.deptid = weeklytransactions.departmentId
Where (vat_rates.vat_from <= weeklytransactions.weekendingdate and business_units.Active = true and business_units.sales=1)
Group By weeklytransactions.weekendingdate, business_units.business_unit Order By fy desc, business_unit, fyweek
Regards
Pete
Assuming I read your question correctly, your problem is about having the result of another SELECT used to be returned by the result of your main query (plus depending on how acquainted you are with SQL, maybe you haven't had the occasion to learn about JOINs?).
You can have subqueries you extract data from within a SELECT, provided you define it within the FROMclause. The following query will work, for example:
SELECT A.a, B.b
FROM A
JOIN (SELECT aggregate(c) FROM C) AS B
Notice that there is no reference to table A within the subquery. Thing is, you cannot just add it like that to the query, as the subquery doesn't know it is a subquery. So the following won't work:
SELECT A.a, B.b
FROM A
JOIN (SELECT aggregate(c) FROM C WHERE C.someValue = A.someValue) AS B
Back to basics. What you want to do here visibly, is to aggregate some data associated to each of the records of another table. For that, you will need merge your SELECT queries and use GROUP BY:
SELECT A.a, aggregate(C.c)
FROM A, C
WHERE C.someValue = A.someValue
GROUP BY A.a
Back to your tables, the following should work:
SELECT w.weekendingdate, FORMAT(MAX(v.Vat_Rate, 3)
FROM weeklytransactions AS w, vat_rates AS v
WHERE v.Vat_From <= w.weekendingdate
GROUP BY w.weekendingdate
Feel free to add and remove fields and conditions as you see fit (I wouldn't be surprised that you'd also want to use a lower bound when filtering the records from vat_rates, since the way I have written it above, for a given weekendingdate, you get records from that week + the weeks before!).
So it looks like my first try did not address the actual problem. With the additional information provided in the comments, as well as the new complete query, let's see how this goes.
We are still missing error messages, but normally the query as written should result in MySQL having the following complaint:
ERROR 1109 (42S02): Unknown table 'vat_rates' in field list
Why? Because the vat_rates table does not appear in the FROM clause, whereas it should. Let's make that more obvious by simplifying the query, removing all references to the business_units table as well as the fields, calculations and order that do not add or remove anything to the problem, leaving us with the following:
SELECT MAX(vat_rates.vat_rate) AS r,
IF(d.vat, w.takings / r, w.takings) AS Total
FROM departments AS d
INNER JOIN weeklytransactions AS w ON w.departmentId = d.deptid
WHERE vat_rates.vat_from <= w.weekendingdate
GROUP BY w.weekendingdate
That cannot work, and will produce the error mentioned above. It looks like there is no FOREIGN ID between the weeklytransactions and vat_rates tables, so we have no choice but to do a CROSS JOIN for the moment, hoping that the condition in the WHERE clause and the aggregate function used to get r are enough to fit the business logic at hand here. The following query should return the expected data instead of an error message (I also remove r since that seems to be an intermediate value judging by the comments that were written):
SELECT IF(d.vat, w.takings / MAX(v.vat_rate), w.takings) AS Total
FROM vat_rates AS v, departments AS d
INNER JOIN weeklytransactions AS w ON w.departmentId = d.deptid
WHERE v.vat_from <= w.weekendingdate
GROUP BY w.weekendingdate
From there, assuming it works, you will only need to put back all the parts I removed to get your final query. I am a tad doubtful about the way the VAT rate is gotten here, but I have no idea what your requirements are in that regard so I leave it up to you to make sure that works as expected.
To match up some new schema to old, I'm having to do some ugly contortions that I figure could be done in a better way. For reference, I asked another question about this match-up process here: Creating View from Related Child Tables
I've placed a simplified example in SQLFiddle but the gist of it is, that the only way I can see reconciling these two different schemas is to do two case statements on the same value, something like this:
SELECT
CASE
WHEN n.FooBarStatusId = 1 OR n.FooBarStatusId = 2
THEN 1
ELSE 0
END as [IsFoo],
CASE
WHEN n.FooBarStatusId = 2
THEN 1
ELSE 0
END as [IsBar]
from Parent p
left join OldStuff o on p.ParentId = o.ParentId
left join NewStuff n on p.ParentId = n.ParentId
Is there a better and/or more efficient way of accomplishing the same thing? These case statements could be hit hundreds of times in a given query and I'm concerned about this specific logic.
I've thought about extracting this specific logic out (it is part of a larger query to build a view) into a temp table or perhaps even a table-valued function, but even still I can't come up with a way around using multiple case statements.
Just corrected grammar...
I found another solution:
select
p.Name,
ISNULL(o.IsFoo, CONVERT(BIT, n.FooBarStatusId)) as [IsFoo],
ISNULL(o.IsBar, CONVERT(BIT, n.FooBarStatusId * (n.FooBarStatusId - 1))) as [IsBar],
from Parent p
left join OldStuff o on p.ParentId = o.ParentId
left join NewStuff n on p.ParentId = n.ParentId
The only one arithmetic solution could be slow:
select
p.Name,
ISNULL(o.IsFoo, CAST( (n.FooBarStatusId % 0.35) * 4 AS int)) AS [IsFoo],
ISNULL(o.IsBar, n.FooBarStatusId/2) [IsBar]
from Parent p
left join OldStuff o on p.ParentId = o.ParentId
left join NewStuff n on p.ParentId = n.ParentId
Personally, I do not like to use the division, because of could be involved floating point operations, that way, it would be very slow.
As you have two columns, you will need two expressions... but they might not have to be CASE expressions. Reading your question, I get the impressions that the only possible values in the column are 0,1,2, and that this is an int type? If that's correct, you can use arithmetic rather than boolean logic to get what you need. Try this:
CAST( (n.FooBarStatusId % .35) * 4 AS int) AS [IsFoo],
n.FooBarStatusId/2 [IsBar]