How can I check whether certain datatables (e.g. "tableA", "tableB" & "tableC") are empty in one query (SQL Server)?
Expected result:
The most important for me is to have ONE result.
It could be true (if all tables are empty) vs false.
Another possibility is the sum of all entries over all tables like 0 (if all tables are empty) or otherwise n.
Example
There are three tables in database: table1, table2 and table3.
All tables are empty. --> Expected result: 0
Table1 has 3 rows, table2 has 0 rows, table3 has 1 row. --> Expected result: 4.
You can get the counts from the tables using union all:
select 'a', count(*) from a union all
select 'b', count(*) from b union all
select 'c', count(*) from c;
However, the fastest way is to use exists:
select (case when not exists (select 1 from a) then 1 else 0 end) as a_is_empty,
(case when not exists (select 1 from b) then 1 else 0 end) as b_is_empty,
(case when not exists (select 1 from c) then 1 else 0 end) as c_is_empty
EDIT:
If you want the total rows in the three tables, just add them up:
select sum(cnt)
from (select 'a', count(*) as cnt from a union all
select 'b', count(*) from b union all
select 'c', count(*) from c
) abc;
I would be wary about using system tables for this operation, if you need exact, up-to-date results. System tables are great in a static environment, where the tables aren't changing, but I suspect your environment is more dynamic.
You also can use this DMV which will query the Count from CACHE only..
SELECT SUM(row_count) AS rows
FROM sys.dm_db_partition_stats
where object_name(object_id) in ('table1','tab1e2')
group by OBJECT_NAME(object_id)
Update as per question:
;with cte
as
(SELECT SUM(row_count) AS rows
FROM sys.dm_db_partition_stats
where object_name(object_id) in ('table1','tab1e2')
group by OBJECT_NAME(object_id))
select sum(rows) as rows from cte
hope below query help you.
SELECT
SCHEMA_NAME(SOS.SCHEMA_ID) + '.' + (SOS.NAME) AS [Table Name]
, (SPS.Rows) AS [Row Count]
, [Heap / Clustered Table] = CASE SPS.INDEX_ID WHEN 0 THEN 'HEAP' ELSE 'CLUSTERED' END
FROM
sys.objects AS SOS
INNER JOIN sys.partitions AS SPS
ON SOS.object_id = SPS.object_id
WHERE
SOS.type = 'U'
AND SPS.index_id < 2
and SPS.Rows =0
ORDER BY [Table Name]
Please Mark me as answer if my post helps you.
Regards
ChetanV
Related
I have three tables A,B and C. I have to detect if any of them have zero rows. As soon as any table with zero row is detected, I do not need to check other ones.
So, one way is I execute three queries separately and after each query I check the number of returned rows. If its non-zero then only I execute the query of next table.
Second way is I write a single query using case-when, something like
select case
when (select count(*) from A = 0)
then 1
else (
select case
when (select count(*) from B = 0)
then 1
else (
select case
when (select count(*) from B = 0)
then 1
else 0
)
)
end as matchResult;
The second method requires lesser code as I have to write a single query and db will do the comparison for me.
My question is whether its overkilling or can I further optimize the query?
EDIT
On further study, I realise that the query above is wrong. However, I can simply do it as
select case
when (select count(*) from A) = 0 and
(select count(*) from B) = 0 and
(select count(*) from C) = 0
then 1
else 0
end as matchResult;
and if I am not wrong, and conditions are checked from left to right and if any one is false, conditions to the right are not checked.
Please confirm this point.
Count is kind of expensive
select 1
where not exits (select * from a)
or not exits (select * from b)
or not exits (select * from c)
One query with three resutls:
select (select count(*) from A) as Acount,
(select count(*) from B) as Bcount,
(select count(*) from C) as Ccount
This instead gives name of the fitst table that is empty:
select case
when (select count(*) from A)=0 then 'A'
when (select count(*) from B)=0 then 'B'
when (select count(*) from C)=0 then 'C'
else 'ops, all have records' -- remove this to have a null
end as first_empty_table
I've the following table with 3 columns: Id, FeatureName and Value:
Id FeatureName Value
-- ----------- -----
1 AAA 10
1 ABB 12
1 BBB 12
2 AAA 15
2 ABB 12
2 ACD 7
3 AAA 10
3 ABB 12
3 CCC 12
.............
Each Id has different features and each Feature has a value for that Id.
I need to write a query which gives me the Ids that have exactly the same features and values than a given one, but only taking into account those whose name starts with 'A'. For example, in the top table, I can use that query to search for all the Ids that have the same features. For example, features with values where Id=1 would result Id=3 with same features starting with 'A' and same values for these features.
I found a couple of different ways to do this, but all of them go very slow when the table has lots of rows (more than hundred of thousands)
The way I obtain the best performance is using the next query:
select a2.Id
from (select a.FeatureName, a.Value
from Table1 a
where a.Id = 1) a1,
(select a.Id, a.FeatureName, a.Value
from Table1 a
where a.FeatureName like 'A%') a2
where a1.FeatureName = a2.FeatureName
and a1.value = a2.value
group by a2.Id
having count(*) = 2
intersect
select a.Id
from Table1 a
where a.FeatureName like 'A%'
group by a.Id
having count(*)= 2
where #nFeatures is the number of features starting by 'A' in Id=1. I counted them before calling this query. I make the intersection to avoid results that have the same parameters than Id=1 but also some others whose name starts with 'A'.
I think that the slowest part is the second subquery:
select a.Id, a.FeaureName, a.Value
from MyTable a
where a.FeatureName = 'A%'
but I don't know how to make it faster. Maybe I will have to play with the indexes.
Any idea of how could I write a fast query for this purpose?
So you want all rows where the combination of FeatureName and Value is not unique? You can use EXISTS:
SELECT t.*
FROM dbo.Table1 t
WHERE t.FeatureName LIKE 'A%'
AND EXISTS(SELECT 1 FROM dbo.Table1 t2
WHERE t.Id <> t2.ID
AND t.FeatureName = t2.FeatureName
AND t.Value = t2.Value)
Demo
how could I write a fast query for this purpose?
If it's not fast enough create an index on FeatureName + Value.
I tried to eliminate the join with MyTable again to select the data for the ID's that have matching FeatureName and Value values. Here's the query:
with joined_set as
(
SELECT
mt1.*, mt2.id as mt2_id, mt2.featurename as mt2_FeatureName, mt2.value as mt2_value
from
(
select *
from mytable
where featurename like 'A%'
) mt1
left join
(
select *
from mytable
where featurename like 'A%'
) mt2
on mt2.id <> mt1.id and mt2.FeatureName = mt1.featurename and mt2.value = mt1.value
)
select distinct id
from joined_set
where id not in
(select id
from joined_set
group by id
having SUM(
CASE
WHEN mt2_id is null THEN 1
ELSE 0
END
) <> 0
);
Here is the SQL Fiddle demo. It has an extra condition in the inline view mt2, to perform this search only for id = 1.
I'm a little dense this morning, I'm not sure if you wanted just the ID's or...
Here's my take on it...
You could probably move the where FeatureName like 'A%' into the inner query to filter the data on the initial table scan.
with dupFeatures (FeatureName, Value, dupCount)
as
(
select FeatureName, Value, count(*) as dupCount from MyTable
group by FeatureName, Value
having count(*) > 1
)
select MyTable.Id, dupFeatures.FeatureName,dupFeatures.Value
from dupFeatures
join MyTable on (MyTable.FeatureName = dupFeatures.FeatureName and
MyTable.Value = dupFeatures.Value )
where dupFeatures.FeatureName like 'A%'
order by FeatureName, Value, Id
A general solution is
With Rows As (
select id
, FeatureName
, Value
, rows = Count(id) OVER (PARTITION BY id)
FROM test
WHERE FeatureName LIKE 'A%')
SELECT a.id aID, b.id bID
FROM Rows a
INNER JOIN Rows b ON a.id < b.id and a.FeatureName = b.FeatureName
and a.rows = b.rows
GROUP BY a.id, b.id
ORDER BY a.id, b.id
to limit the solution to a group just add a WHERE condition on the main query for a.ID. The CTE is needed to get the correct number of rows for each id
SQLFiddle demo, in the demo I changed little the test data to have a another couple of ID with only one of the FeatureName of 1 and 3
I am writing data to a table and allocating a "group-id" for each batch of data that is written. To illustrate, consider the following table.
GroupId Value
------- -----
1 a
1 b
1 c
2 a
2 b
3 a
3 b
3 c
3 d
In this example, there are three groups of data, each with similar but varying values.
How do I query this table to find a group that contains a given set of values? For instance, if I query for (a,b,c) the result should be group 1. Similarly, a query for (b,a) should result in group 2, and a query for (a, b, c, e) should result in the empty set.
I can write a stored procedure that performs the following steps:
select distinct GroupId from Groups -- and store locally
for each distinct GroupId: perform a set-difference (except) between the input and table values (for the group), and vice versa
return the GroupId if both set-difference operations produced empty sets
This seems a bit excessive, and I hoping to leverage some other commands in SQL to simplify. Is there a simpler way to perform a set-comparison in this context, or to select the group ID that contains the exact input values for the query?
This is a set-within-sets query. I like to solve it using group by and having:
select groupid
from GroupValues gv
group by groupid
having sum(case when value = 'a' then 1 else 0 end) > 0 and
sum(case when value = 'b' then 1 else 0 end) > 0 and
sum(case when value = 'c' then 1 else 0 end) > 0 and
sum(case when value not in ('a', 'b', 'c') then 1 else - end) = 0;
The first three conditions in the having clause check that each elements exists. The last condition checks that there are no other values. This method is quite flexible, for various exclusions and inclusion conditions on the values you are looking for.
EDIT:
If you want to pass in a list, you can use:
with thelist as (
select 'a' as value union all
select 'b' union all
select 'c'
)
select groupid
from GroupValues gv left outer join
thelist
on gv.value = thelist.value
group by groupid
having count(distinct gv.value) = (select count(*) from thelist) and
count(distinct (case when gv.value = thelist.value then gv.value end)) = count(distinct gv.value);
Here the having clause counts the number of matching values and makes sure that this is the same size as the list.
EDIT:
query compile failed because missing the table alias. updated with right table alias.
This is kind of ugly, but it works. On larger datasets I'm not sure what performance would look like, but the nested instances of #GroupValues key off GroupID in the main table so I think as long as you have a good index on GroupID it probably wouldn't be too horrible.
If Object_ID('tempdb..#GroupValues') Is Not Null Drop Table #GroupValues
Create Table #GroupValues (GroupID Int, Val Varchar(10));
Insert #GroupValues (GroupID, Val)
Values (1,'a'),(1,'b'),(1,'c'),(2,'a'),(2,'b'),(3,'a'),(3,'b'),(3,'c'),(3,'d');
If Object_ID('tempdb..#FindValues') Is Not Null Drop Table #FindValues
Create Table #FindValues (Val Varchar(10));
Insert #FindValues (Val)
Values ('a'),('b'),('c');
Select Distinct gv.GroupID
From (Select Distinct GroupID
From #GroupValues) gv
Where Not Exists (Select 1
From #FindValues fv2
Where Not Exists (Select 1
From #GroupValues gv2
Where gv.GroupID = gv2.GroupID
And fv2.Val = gv2.Val))
And Not Exists (Select 1
From #GroupValues gv3
Where gv3.GroupID = gv.GroupID
And Not Exists (Select 1
From #FindValues fv3
Where gv3.Val = fv3.Val))
I'm running a netezza sql process as part of a shell script and in one of the sql codes, I want it to raise an ERROR or exception if the number of rows from 2 different tables don't match.
SQL Code:
/* The following 2 tables should return the same number of rows to make sure the process is correct */
select count(*)
from (
select distinct col1, col2,col3
from table_a
where week > 0 and rec >= 1
) as x ;
select count(*)
from (
select distinct col1, col2, col3
from table_b
) as y ;
How do I compare the 2 row counts and raise an exception/ERROR in the netezza SQL process, so that it exits the process, if the 2 row counts aren't equal ?
I agree a script is the best option. However you could still do the check in your SQL itself by using a cross join
Select a.*
from Next_Step_table a cross join
(select case when y.y_cnt is null then 'No Match' else 'Match' end as match
from (select count(*) as x_cnt
from ( select distinct col1, col2,col3
from table_a
where week > 0 and rec >= 1
)) x left outer join
(select count(*) as y_cnt
from (select distinct col1, col2, col3
from table_b
)) y on x.x_cnt=y.y_cnt) match_tbl
where match_tbl.match='Match'
i'm guessing the best solution here is to do it in the script.
i.e store the result of count(*) in variables, then compare them. nzsql has command line options to only return the result data of a single query.
If it must be done in plain SQL, a horribly, horrible kludge that will work is to use divide-by-zero. It's ugly but I've used it before when testing stuff. off the top of my head:
with
subq_x as select count(*) c1 .... ,
subq_y as select count(*) c2 ...
select (case when (subq_x.c1 != subq_y.c1) then 1/0 else 1 end) counts_match;
Did I mention this is ugly ?
so basicially there is 1 question and 1 problem:
1. question - when I have like 100 columns in a table(and no key or uindex is set) and I want to join or subselect that table with itself, do I really have to write out every column name?
2. problem - the example below shows the 1. question and my actual SQL-statement problem
Example:
A.FIELD1,
(SELECT CASE WHEN B.FIELD2 = 1 THEN B.FIELD3 ELSE null FROM TABLE B WHERE A.* = B.*) AS CASEFIELD1
(SELECT CASE WHEN B.FIELD2 = 2 THEN B.FIELD4 ELSE null FROM TABLE B WHERE A.* = B.*) AS CASEFIELD2
FROM TABLE A
GROUP BY A.FIELD1
The story is: if I don't put the CASE into its own select statement then I have to put the actual rowname into the GROUP BY and the GROUP BY doesn't group the NULL-value from the CASE but the actual value from the row. And because of that I would have to either join or subselect with all columns, since there is no key and no uindex, or somehow find another solution.
DBServer is DB2.
So now to describing it just with words and no SQL:
I have "order items" which can be divided into "ZD" and "EK" (1 = ZD, 2 = EK) and can be grouped by "distributor". Even though "order items" can have one of two different "departements"(ZD, EK), the fields/rows for "ZD" and "EK" are always both filled. I need the grouping to consider the "departement" and only if the designated "departement" (ZD or EK) is changing, then I want a new group to be created.
SELECT
(CASE WHEN TABLE.DEPARTEMENT = 1 THEN TABLE.ZD ELSE null END) AS ZD,
(CASE WHEN TABLE.DEPARTEMENT = 2 THEN TABLE.EK ELSE null END) AS EK,
TABLE.DISTRIBUTOR,
sum(TABLE.SOMETHING) AS SOMETHING,
FROM TABLE
GROUP BY
ZD
EK
TABLE.DISTRIBUTOR
TABLE.DEPARTEMENT
This here worked in the SELECT and ZD, EK in the GROUP BY. Only problem was, even if EK was not the designated DEPARTEMENT, it still opened a new group if it changed, because he was using the real EK value and not the NULL from the CASE, as I was already explaining up top.
And here ladies and gentleman is the solution to the problem:
SELECT
(CASE WHEN TABLE.DEPARTEMENT = 1 THEN TABLE.ZD ELSE null END) AS ZD,
(CASE WHEN TABLE.DEPARTEMENT = 2 THEN TABLE.EK ELSE null END) AS EK,
TABLE.DISTRIBUTOR,
sum(TABLE.SOMETHING) AS SOMETHING,
FROM TABLE
GROUP BY
(CASE WHEN TABLE.DEPARTEMENT = 1 THEN TABLE.ZD ELSE null END),
(CASE WHEN TABLE.DEPARTEMENT = 2 THEN TABLE.EK ELSE null END),
TABLE.DISTRIBUTOR,
TABLE.DEPARTEMENT
#t-clausen.dk: Thank you!
#others: ...
Actually there is a wildcard equality test.
I am not sure why you would group by field1, that would seem impossible in your example. I tried to fit it into your question:
SELECT FIELD1,
CASE WHEN FIELD2 = 1 THEN FIELD3 END AS CASEFIELD1,
CASE WHEN FIELD2 = 2 THEN FIELD4 END AS CASEFIELD2
FROM
(
SELECT * FROM A
INTERSECT
SELECT * FROM B
) C
UNION -- results in a distinct
SELECT
A.FIELD1,
null,
null
FROM
(
SELECT * FROM A
EXCEPT
SELECT * FROM B
) C
This will fail for datatypes that are not comparable
No, there's no wildcard equality test. You'd have to list every field you want tested individually. If you don't want to test each individual field, you could use a hack such as concatenating all the fields, e.g.
WHERE (a.foo + a.bar + a.baz) = (b.foo + b.bar + b.az)
but either way, you're listing all of the fields.
I might tend to solve it something like this
WITH q as
(SELECT
Department
, (CASE WHEN DEPARTEMENT = 1 THEN ZD
WHEN DEPARTEMENT = 2 THEN EK
ELSE null
END) AS GRP
, DISTRIBUTOR
, SOMETHING
FROM mytable
)
SELECT
Department
, Grp
, Distributor
, sum(SOMETHING) AS SumTHING
FROM q
GROUP BY
DEPARTEMENT
, GRP
, DISTRIBUTOR
If you need to find all rows in TableA that match in TableB, how about INTERSECT or INTERSECT DISTINCT?
select * from A
INTERSECT DISTINCT
select * from B
However, if you only want rows from A where the entire row matches the values in a row from B, then why does your sample code take some values from A and others from B? If the row matches on all columns, then that would seem pointless. (Perhaps your question could be explained a bit more fully?)