Here is the query I am using to generate last date of each week. However the filter does not seem to take affect. and the starting date I get is "2016-01-03".
SELECT TO_DATE(last_day(DATEADD(DAY, SEQ4()*7, '2016-01-01 00:00:00'), 'week')) AS WEEK_LAST_DATE
FROM TABLE(GENERATOR(ROWCOUNT=>1000))
WHERE WEEK_LAST_DATE > '2016-09-07';
The following works though:
SELECT * from (
SELECT TO_DATE(last_day(DATEADD(DAY, SEQ4()*7, '2016-01-01 00:00:00'), 'week')) AS WEEK_LAST_DATE
FROM TABLE(GENERATOR(ROWCOUNT=>1000))
) as A
WHERE A.WEEK_LAST_DATE > '2016-09-07';
Why does the first query not work?
In general in SQL, you can't refer to an expression defined in the select clause in the same scope - left apart the order by clause. Typically, this raises a syntax error:
select t.*, 'abc' as newcol
from mytable t
where newcol = 'abc'
newcol is defined in the select clause, hence not available in the where clause. This is typically worked around by computing the value in an inner scope, then using it for filtering in an outer scope: subqueries, lateral joins, and common table expressions are the most common approaches. So:
select *
from (
select t.*, 'abc' as newcol
from mytable t
) t
where newcol = 'abc'
I am surprised that your first query even compiles; it may be some Snowflake-specific thing. But the second query is indeed the right way to do what you want:
Related
Given this example:
Pivoted Table
And the desired output is the following:
Desired Result
So my question is. I'm running a proprietary server which I cannot mention here and this server does not support UNPIVOT operator. I have tried so far the following:
SELECT week,
day,
username,
CASE
WHEN main_cat_1 = "cars" THEN "cars"
WHEN main_cat_2 = "vans" THEN "vans"
ELSE null END AS main_cat,
CASE
WHEN sub_cat_1.1 = "dirty" THEN "dirty"
WHEN sub_cat_1.2 = "stalled" THEN "stalled"
ELSE null END AS sub_cat
FROM table1
The issue with this approach is that because of short-circuit evaluation after the first TRUE valueit does not seem to work properly and does not return the expected values.
SELECT week,
day,
username,
main_cat_1 as category,
sub_cat_1.1 as subcategory
FROM table1
UNION
SELECT week,
day,
username,
main_cat_1,
sub_cat_1.2
FROM table1
UNION
...etc.
I have an SQL query in which I need to take the output of a subquery and use it more than once. My existing query works, but only if I repeat the subquery each time I need it. Unfortunately the subquery is complex, and takes time to execute - meaning that multiple iterations really slow the whole thing down.
I have read that you can use the "WITH" statement to assign a subquery output to a variable, in order to re-use that variable. However the problem I'm having is that within the subquery, I need to reference values from the main query. And it appears that if I use WITH - before the main query SELECT - then those references are not recognised. I'll give you a simplified example:
WITH
DateX AS
(
SELECT
MAX(TableSub.Date)
FROM
TableA TableSub
WHERE
TableSub.ID = TableMain.ID
AND TableSub.Event = 'AnotherEvent'
AND TableSub.Date BETWEEN '01-Jan-2015' AND '31-Dec-2015'
)
SELECT
TableMain.ID
FROM
TableA TableMain
WHERE
TableMain.Event = 'MainEvent'
AND TableMain.Date >= DateX
AND (
SELECT
TableSub2.ID
FROM
TableA TableSub2
WHERE
TableSub2.ID = TableMain.ID
TableSub2.Event = 'ThirdEvent'
AND TableSub2.Date <= DateX
) IS NULL
I hope this is clear. It's a simplified version of what I have, but you can see that DateX is used in more than one place: within the main query, and within a subquery. However the problem is that when DateX is defined by WITH, I need to link the ID back to the ID of the main query. And it's not working...
I would be grateful for any advice on this. Am I doing it wrong? Is there a way, or is it just impossible? If so, then should I be using another approach entirely? Thanks.
A better way:
SELECT ID
FROM (
SELECT ID,
"Date",
Event,
LAST_VALUE( CASE Event WHEN 'AnotherEvent' THEN "Date" END IGNORE NULLS )
OVER ( PARTITION BY ID ORDER BY "Date"
ROWS BETWEEN UNBOUNDED PRECEEDING AND UNBOUNDED FOLLOWING
) AS another_date,
FIRST_VALUE( CASE Event WHEN 'ThirdEvent' THEN "Date" END IGNORE NULLS )
OVER ( PARTITION BY ID ORDER BY "Date"
ROWS BETWEEN UNBOUNDED PRECEEDING AND UNBOUNDED FOLLOWING
) AS third_date
FROM TableA
WHERE Event IN ( 'MainEvent', 'ThirdEvent' )
OR ( Event = 'AnotherEvent' AND EXTRACT( YEAR FROM "Date" ) = 2015 )
)
WHERE Event = 'MainEvent'
AND "Date" >= another_date
AND ( third_date IS NULL OR third_date > another_date );
You need to join your DateX CTE on the ID column. Something like:
WITH
DateX AS
(
SELECT
TableSub.ID,
MAX(TableSub.Date) AS MaxDate
FROM
TableA TableSub
WHERE
AND TableSub.Event = 'AnotherEvent'
AND TableSub.Date >= DATE '2015-01-01'
AND TableSub.Date < DATE '2016-01-01'
GROUP BY
TableSub.ID
)
SELECT
TableMain.ID
FROM
TableA TableMain
JOIN
DateX
ON
DateX.ID = TableMain.ID
WHERE
TableMain.Event = 'MainEvent'
AND TableMain.Date >= DateX.MaxDate
AND (
SELECT
TableSub2.ID
FROM
TableA TableSub2
JOIN
DateX
ON
DateX.ID = TableSub2.ID
WHERE
TableSub2.ID = TableMain.ID
TableSub2.Event = 'ThirdEvent'
AND TableSub2.Date <= DateX.MaxDate
) IS NULL
The CTE also needs a column alias for the aggregate; and as you need to join in the ID, you need to include that and group by it.
The last subquery looks odd; you might want NOT EXISTS rather than IS NULL if you're looking for no record. Perhaps your real query is using an aggregate, but even so that might be quicker.
This still may not be the best approach but it's hard to tell from your example. Hitting the same table three times may be unnecessarily expensive.
Working in Oracle 11g, I have a need to select a datum corresponding to an input value when that value exists in a table, and to instead select a static default value when it does not. The best way I could find to accomplish this was to write something like this:
SELECT desired_datum
FROM (
--Try to get explicit datum
SELECT desired_datum, 1 AS was_found
FROM data_table
WHERE the_key = &input_value
UNION
--Get default datum
SELECT 'default' AS desired_datum, 0 AS was_found
FROM dual
--Put explicit datum on top, if it exists
ORDER BY was_found DESC
) finder
WHERE ROWNUM <=1;
It seems like there must be some idiomatic way to do this which doesn't depend on this strange use of ORDER BY, but I couldn't find it. Does anyone know of any better methods?
You can also do this with aggregation:
SELECT COALESCE(MAX(desired_datum), 'default')
FROM data_table
WHERE the_key = &input_value
This should be a simpler version of what you did:
SELECT NVL(desired_datum, 'default') AS desired_datum
FROM DUAL LEFT JOIN data_table ON the_key = &input_value
I've found basic answer for replacing the Oracle's "CONNECT BY LEVEL" in this question but my case is little bit more complicated:
Basically things that I want to replace looks like this:
...
UNION ALL
Select
adate, 'ROAD' as TSERV_ID, 0 AS EQ_NBR
from
(SELECT
to_date(sysdate - 732,'dd/mm/yy') + rownum -1 as adate, rownum
FROM
(select rownum
from dual
connect by level <= 732)
WHERE rownum <= 732)
UNION ALL
Select
adate, 'PORTPACK' as TSERV_ID, 0 AS EQ_NBR
from
(SELECT
to_date(sysdate - 732,'dd/mm/yy') + rownum -1 as adate, rownum
FROM
(select rownum from dual connect by level <= 732)
WHERE rownum <= 732)
UNION ALL
....
Now, the single dual connect is easy, even if this is apparently not very efficient method
WITH CTE AS (
SELECT dateadd(day,-720,CONVERT (date, GETDATE())) as Datelist
UNION ALL
SELECT dateadd(day,1,Datelist)
FROM CTE
WHERE datelist < getdate() )
SELECT *,'ROAD' as Tserv_ID , 0 as EQ_NBR FROM CTE
option (maxrecursion 0)
repeating the union is hard because I get an error:
Incorrect syntax near the keyword 'with'. If this statement is a common table expression, an xmlnamespaces clause or a change tracking context clause, the previous statement must be terminated with a semicolon.
There are more parts of this union that I've provided here; I've tried to use the "WITH" only at start but no luck. Am I missing something obvious here?
EDIT: There is of course big question WHY I am even trying to do such thing: Personally, I wouldn't, but at the other end of the query there is a huge Crystal Report that runs once every month and which accepts data in this particular format. End of the FULL query's output is something like
3 columns of data
3 Columns of data
...
Currentdate-732,"ROAD",0
Currentdate -731,"ROAD",0
...
Currentdate, "ROAD,"0"
Currentdate -732, "PORTPAK", 0
Currentdate -731, "PORTPAK", 0
etc.
Are you trying to do:
WITH CTE1 AS (...),
CTE2 AS (...)
SELECT stuff FROM CTE1
UNION ALL
SELECT stuff FROM CTE2;
? This is a common challenge, I guess it is not very discoverable that in order to use more than one CTE, you just separate them with a comma.
That all said, it seems like you are just trying to generate a series of dates. A recursive CTE (never mind a series of many of them) is not the most efficient way to do this. Instead of telling us you want to replace CONNECT BY LEVEL and showing us the syntax you've tried, why don't you just show or describe the output you want? We've already got an appreciation that you've tried something on your own (thanks!) but we'd rather give you an efficient solution than bridging the gap to an inefficient one.
As an example, here is something that requires a lot less redundant code, and ( think gives you what you're after:
DECLARE #n INT = 722, #d DATE = CURRENT_TIMESTAMP;
;WITH v AS (SELECT v FROM (VALUES('ROAD'),('PORTPACK')) AS v(v)),
n AS (SELECT TOP (#n) n = ROW_NUMBER() OVER (ORDER BY number)
FROM master.dbo.spt_values ORDER BY n)
SELECT Datelist = DATEADD(DAY, 2-n.n, #d), Tserv_ID = v.v, EQ_NBR = 0
FROM n CROSS JOIN v
ORDER BY Tserv_ID, Datelist;
In a query I create lots of fields using the CASE expression.
I need to reference these fields later on in the query but it seems I can't access the field using its alias - I have to repeat the CASE expression every time I want to reference its value.
Is there a simple way to access these fields?
You can use CTEs (assuming SQL Server 2005+), like this very basic example:
DECLARE #Val INT
SET #Val = 1
;WITH CTEExample AS
(
SELECT CASE #Val WHEN 1 THEN 'A' ELSE 'B' END AS MyCaseField1
)
SELECT * FROM CTEExample WHERE MyCaseField1 = 'A'
why not simply make a subquery
eg
SELECT foo.column
FROM (
SELECT
CASE WHEN yourcase THEN 'a'
ELSE 'b'
END AS 'column'
FROM yourtable) AS foo
but this can be done with CTEs either (look at this answer)
You can also use CROSS APPLY for this as in this tip by Itzik Ben Gan.
SELECT SalesOrderID, OrderDate, Week_Day
FROM Sales.SalesOrderHeader
CROSS APPLY
(SELECT DATEPART(weekday, DATEADD(day, ##DATEFIRST - 7, OrderDate)) AS Week_Day) AS A
WHERE Week_Day NOT IN (1, 7);
You should be aware that reusing aliases in a where clause will render the predicate unsargable however so should be used with caution (this applies regardless of whether you use APPLY or a CTE)