I am looking for a query where I can get unique values(5) in a table. For example.
The table consists of more 100+ columns. Is there any way I can get unique values.
I am using google big query and tried this option
select col1 col2 ... coln
from tablename
where col1 is not null and col2 is not null
group by col1,col2... coln
order by col1, col2... coln
limit 5
But problem is it gives zero records if all the column are null
Thanks
R
I think you might be able to do this in Google bigquery, assuming that the types for the columns are compatible:
select colname, colval
from (select 'col1' as colname, col1 as colvalue
from t
where col1 is not null
group by col1
limit 5
),
(select 'col2' as colname, col2 as colvalue
from t
where col2 is not null
group by col2
limit 5
),
. . .
For those not familiar with the syntax, a comas in the from clause means union all, not cross join in this dialect. Why did they have to change this?
Try This one, i hope it works
;With CTE as (
select * ,ROW_NUMBER () over (partition by isnull(col1,''),isnull(col2,'')... isnull(coln,'') order by isnull(col1,'')) row_id
from tablename
) select * from CTE where row_id =1
Related
Quite often I have to do queries like below:
select col1, max(id)
from Table
where col2 = 'value'
and col3 = ( select max(col3)
from Table
where col2 = 'value'
)
group by col1
Are there any other ways to avoid subqueries and temp tables? Basically I need a group by on all the rows with a particular max value. Assuming all proper indices are used.
You can use an OLAP function to achieve this. I would say this solution is marginally better in that your predicates are not duplicated between the main query and subquery, so you don't violate DRY:
SELECT *
FROM (
select col1, max(id) as max_id,
RANK() OVER (PARTITION BY col1 ORDER BY col3 DESC) AS irow
from [Member]
where col2 = 'value'
group by col1
) subquery
WHERE subquery.irow = 1
I have a select that look like this:
SELECT * FROM (SELECT DISTICT COL1, COL2, COL3
FROM view a WHERE conditions ....
) QUERY
WHERE CONDITIONS... LIMIT 20 OFFSET 0
I'm executing this from java and I need this query return an unique id.
So i try:
SELECT TRIM(CHAR(HEX(GENERATE_UNIQUE()))) AS GUID, QUERY.* FROM (SELECT DISTICT COL1, COL2, COL3
FROM view a WHERE conditions ....
) QUERY
WHERE CONDITIONS... LIMIT 20 OFFSET 0
This one return an error telling me I can't use this function in that place.
If i try:
SELECT * FROM (SELECT DISTINCT TRIM(CHAR(HEX(GENERATE_UNIQUE()))) AS GUID, COL1, COL2, COL3
FROM view a WHERE conditions ....
) QUERY
WHERE CONDITIONS... LIMIT 20 OFFSET 0
I have duplicated rows because it is like I execute query wihout DISTINCT
Does anyone know a way to do it?
I don't know DB2 version (I have tried all solutions from How to check db2 version )
If a numeric id would do, how about just using row_number():
SELECT CAST(ROW_NUMBER() OVER (ORDER BY COL1, COL2, COL3) as VARCHAR(255)) as unique_id,
QUERY.*
FROM (SELECT DISTICT COL1, COL2, COL3
FROM view a
WHERE conditions ....
) QUERY
WHERE CONDITIONS...
LIMIT 20 OFFSET 0
I have a SQLite table like this:
Col1 Col2 Col3
1 ABC Bill
2 CDE Fred
3 FGH Jack
4 CDE June
I would like to find the row containing a Col2 value of CDE which has the max Col1 value i.e. in this case June. Or, put another way, the most recently added row with a col2 value of CDE, as Col1 is an auto increment column. What is an SQL query string to achieve this? I need this to be efficient as the query will run many iterations in a loop.
Thanks.
SELECT * FROM table WHERE col2='CDE' ORDER BY col1 DESC LIMIT 1
in case if col1 wasn't an increment it would go somewhat like
SELECT *,MAX(col1) AS max_col1 FROM table WHERE col2='CDE' GROUP BY col2 LIMIT 1
Try this:
SELECT t1.*
FROM table1 t1
INNER JOIN
(
SELECT MAX(col1) MAXID, col2
FROM table1
GROUP BY col2
) t2 ON t1.col1 = t2.maxID AND t1.col2 = t2.col2
WHERE t1.col2 = 'CDE';
SQL Fiddle Demo1
1: This demo is mysql, but it should work fine with the same syntax in sqlite.
Use a subquery such as:
SELECT Col1, Col2, Col3
FROM table
WHERE Col1 = (SELECT MAX(Col1) FROM table WHERE Col2='CDE')
Add indexes as appropriate, e.g. clustered index on Col1 and another nonclustered index on Col2 to speed up the subquery.
In SQLite 3.7.11 and later, the simplest query would be:
SELECT *, max(Col1) FROM MyTable WHERE Col2 = 'CDE'
As shown by EXPLAIN QUERY PLAN, both this and passingby's query are most efficient, if there is an index on Col2.
If you'd want to see the correspondig values for all Col2 values, use a query like this instead:
SELECT *, max(Col1) FROM MyTable GROUP BY Col2
In my table,some records have all column values are the same, except one. I need write a query to get those records. what's the best way to do it? the table is like this:
colA colB colC
a b c
a b d
a b e
What's the best way to get all records with all the columns? Thanks for everyone's help.
Assuming you know that column3 will always be different, to get the rows that have more than one value:
SELECT Col1, Col2
FROM Table t
GROUP BY Col1, Col2
HAVING COUNT(distinct col3) > 1
If you need all the values in the three columns, then you can join this back to the original table:
SELECT t.*
FROM table t join
(SELECT Col1, Col2
FROM Table t
GROUP BY Col1, Col2
HAVING COUNT(distinct col3) > 1
) cols
on t.col1 = cols.col1 and t.col2 = cols.col2
Just select those rows that have the different values:
SELECT col1, col2
FROM myTable
WHERE colWanted != knownValue
If this is not what you are looking for, please post examples of the data in the table and the wanted output.
How about something like
SELECT Col1, Col2
FROM Table
GROUP BY Col1, Col2
HAVING COUNT(*) = 1
This will give you Col1, Col2 that have unique data.
Assuming col3 has the difs
SELECT Col1, Col2
FROM Table
GROUP BY Col1, Col2
HAVING COUNT(*) > 1
OR TO SHOW ALL 3 COLS
SELECT Col1, Col2, Col3
FROM Table1
GROUP BY Col1, Col2, Col3
HAVING COUNT(Col3) > 1
This is my view:
Create View [MyView] as
(
Select col1, col2, col3 From Table1
UnionAll
Select col1, col2, col3 From Table2
)
I need to add a new column named Id and I need to this column be unique so I think to add new column as identity. I must mention this view returned a large of data so I need a way with good performance, And also I use two select query with union all I think this might be some complicated so what is your suggestion?
Use the ROW_NUMBER() function in SQL Server 2008.
Create View [MyView] as
SELECT ROW_NUMBER() OVER( ORDER BY col1 ) AS id, col1, col2, col3
FROM(
Select col1, col2, col3 From Table1
Union All
Select col1, col2, col3 From Table2 ) AS MyResults
GO
The view is just a stored query that does not contain the data itself so you can add a stable ID. If you need an id for other purposes like paging for example, you can do something like this:
create view MyView as
(
select row_number() over ( order by col1) as ID, col1 from (
Select col1 From Table1
Union All
Select col1 From Table2
) a
)
There is no guarantee that the rows returned by a query using ROW_NUMBER() will be ordered exactly the same with each execution unless the following conditions are true:
Values of the partitioned column are unique. [partitions are parent-child, like a boss has 3 employees][ignore]
Values of the ORDER BY columns are unique. [if column 1 is unique, row_number should be stable]
Combinations of values of the partition column and ORDER BY columns are unique. [if you need 10 columns in your order by to get unique... go for it to make row_number stable]"
There is a secondary issue here, with this being a view. Order By's don't always work in views (long-time sql bug). Ignoring the row_number() for a second:
create view MyView as
(
select top 10000000 [or top 99.9999999 Percent] col1
from (
Select col1 From Table1
Union All
Select col1 From Table2
) a order by col1
)
Using "row_number() over ( order by col1) as ID" is very expensive.
This way is much more efficient in cost:
Create View [MyView] as
(
Select ID = isnull(cast(newid() as varchar(40)), '')
, col1
, col2
, col3
From Table1
UnionAll
Select ID = isnull(cast(newid() as varchar(40)), '')
, col1
, col2
, col3
From Table2
)
use ROW_NUMBER() with "order by (select null)" this will be less expensive and will get your result.
Create View [MyView] as
SELECT ROW_NUMBER() over (order by (select null)) as id, *
FROM(
Select col1, col2, col3 From Table1
Union All
Select col1, col2, col3 From Table2 ) R
GO