I have a question about CTEs. You can start of a sql statement by WITH and then you can construct one or multiple CTE queries, which you then in the end can make (in this case) a select on.
My question is: will all CTE queries be executed or only the ones who are being used?
E.g.
WITH cte_1
as (
Select * from table1
),
cte_2
as (
Select * from table2
)
Select * from cte_1
Will this mean that a select will be executed on table1 and table2?
To complete Master Gordon's answer (I dare) :
if you declare 2 cte, and use none of them, you also get that error message
with cte as (select 1/0 as val), cte2 as (select 1/0 as val)
select 1
Msg 422 Level 16 State 4 Line 2
Common table expression defined but not used.
But if you use at least one, the statement is accepted :
with cte_divide_by_zero as (select 1/0 as val), cte_legit as (select 'it works' as val)
select * from cte_divide_by_zero
Msg 8134 Level 16 State 1 Line 1
Divide by zero error encountered.
And if you select the other CTE, it proves that your unused CTE is never executed as no error occurs :
with cte_divide_by_zero as (select 1/0 as val), cte_legit as (select 'it works' as val)
select * from cte_legit
val
--------
it works
I get this message:
Msg 422 Level 16 State 4 Line 2
Common table expression defined but not used.
when running:
with cte as (select 1/0 as val)
select 1
Here is a db<>fiddle.
Related
WITH tb_testl AS （
SELECT 1 AS id ,'hehe' AS value
UNION ALL
SELECT 1 AS id, '1' AS value
UNION ALL
SELECT 2 AS id, '2' AS value
UNION ALL
SELECT 2 AS id, '2' AS value
), tb_test2 AS (
SELECT CONVERT(INT , value) AS value FROM tb_testl WHERE id = 2
)
SELECT * FROM tb_test2 WHERE value = 2;
this sql will cause error
Conversion failed when converting the varchar value 'hehe' to data
type int.
but the table tb_test2 dosen't have the value 'hehe' which is in the anthor table tb_test1. And I found that this sql will work well if I don't append the statement WHERE value = 2; .I've tried ISNUMBERIC function but it didn't work.
version:mssql2008 R2
With respect to the why this occurs:
There is a Logical Processing Order, which describes the order in which clauses are evaluated. The order is:
FROM
ON
JOIN
WHERE
GROUP BY
WITH CUBE or WITH ROLLUP
HAVING
SELECT
DISTINCT
ORDER BY
TOP
You can also see the processing order when you SET SHOWPLAN_ALL ON. For this query, the processing is as follows:
Constant scan - this is the FROM clause, which consists of hard coded values, hence the constants.
Filter - this is the WHERE clause. While it looks like there are two where clauses (WHERE id = 2 and WHERE value = 2). SQL Server sees this differently, it considers a single WHERE clause: WHERE CONVERT(INT , value) = 2 AND id = 2.
Compute scaler. This is the CONVERT function in the select.
Because both WHERE clauses are executed simultaneously, the hehe value is not filtered out of the CONVERT scope.
Effectively, the query is simplified to something like:
SELECT CONVERT(INT, tb_testl.value) AS Cvalue
FROM (
SELECT 1 AS id
, 'hehe' AS value
UNION ALL
SELECT 1 AS id
, '1' AS value
UNION ALL
SELECT 2 AS id
, '2' AS value
UNION ALL
SELECT 2 AS id
, '2' AS value
) tb_testl
WHERE CONVERT(INT, tb_testl.value) = 2
AND tb_testl.id = 2
Which should clarify why the error occurs.
With SQL, you cannot read code in the same way as imperative languages like C. Lines of SQL code are not necessarily (mostly not at all, in fact) executed in the same order it is written in. In this case, it's an error to think the inner where is executed before the outer where.
SQL Server does not guarantee the order of processing of statements (with one exception below). That is, there is no guarantee that WHERE filtering happens before the SELECT. Or that one CTE is evaluated before another. This is considered an advantage because it allows SQL Server to rearrange the processing to optimize performance (although I consider the issue that you are seeing a bug).
Obviously, the problem is in this part of the code:
tb_test2 AS (
SELECT CONVERT(INT, value) AS value
FROM tb_testl
WHERE id = 2
)
(Well, actually, it is where tb_test2 is referenced.)
What is happening is that SQL Server pushes the CONVERT() to where the values are being read, so the conversion is attempted before the WHERE clause is processed. Hence, the error.
In SQL Server 2012+, you can easily solve this using TRY_CNVERT():
tb_test2 AS (
SELECT TRY_CONVERT(INT, value) AS value
FROM tb_testl
WHERE id = 2
)
However, that doesn't work in SQL Server 2008. You can use the fact that CASE does have some guarantees on the order of processing:
tb_test2 AS (
SELECT (CASE WHEN value NOT LIKE '%[^0-9]%' THEN CONVERT(INT, value)
END) AS value
FROM tb_testl
WHERE id = 2
)
error caused by this part of statement
), tb_test2 AS (
SELECT CONVERT(INT , value) AS value FROM tb_testl WHERE id = 2
value has type of varchar and 'hehe' value cannot be converted to integer
WITH tb_testl AS （
SELECT 1 AS id ,'hehe' AS value
UPDATE: sql try convert all value(s) to integer in you statement. to avoid error rewrite statement as
WITH tb_testl AS (
SELECT 1 AS id ,'hehe' AS value
UNION ALL SELECT 1 AS id, '1' AS value
UNION ALL SELECT 2 AS id, '2' AS value
UNION ALL SELECT 2 AS id, '2' AS value
), tb_test2 AS (
SELECT value AS value FROM tb_testl WHERE id = 2
),
tb_test3 AS (
SELECT cast(value as int) AS value FROM tb_test2
)
SELECT * FROM tb_test3
I have noticed strange behaviour in some SQL code used for address matching at the company I work for & have created some test SQL to illustrate the issue.
; WITH Temp (Id, Diff) AS (
SELECT 9218, 0
UNION
SELECT 9219, 0
UNION
SELECT 9220, 0
)
SELECT TOP 1 * FROM Temp ORDER BY Diff DESC
Returns 9218 but
; WITH Temp (Id, Name) AS (
SELECT 9218, 'Sonnedal'
UNION
SELECT 9219, 'Lammermoor'
UNION
SELECT 9220, 'Honeydew'
)
SELECT TOP 1 *, DIFFERENCE(Name, '') FROM Temp ORDER BY DIFFERENCE(Name, '') DESC
returns 9219 even though the Difference() is 0 for all records as you can see here:
; WITH Temp (Id, Name) AS (
SELECT 9218, 'Sonnedal'
UNION
SELECT 9219, 'Lammermoor'
UNION
SELECT 9220, 'Honeydew'
)
SELECT *, DIFFERENCE(Name, '') FROM Temp ORDER BY DIFFERENCE(Name, '') DESC
which returns
9218 Sonnedal 0
9219 Lammermoor 0
9220 Honeydew 0
Does anyone know why this happens? I am writing C# to replace existing SQL & need to return the same results so I can test that my code produces the same results. But I can't see why the actual SQL used returns 9219 rather than 9218 & it doesn't seem to make sense. It seems it's down to the Difference() function but it returns 0 for all the record in question.
When you call:
SELECT TOP 1 *, DIFFERENCE(Name, '')
FROM Temp l
ORDER BY DIFFERENCE(Name, '') DESC
All three records have a DIFFERENCE value of zero, and hence SQL Server is free to choose from any of the three records for ordering. That is to say, there is no guarantee which order you will get. The same is true for your second query. Actually, it is possible that the ordering for the same query could even change over time. In practice, if you expect a certain ordering, you should provide exact logic for it, e.g.
SELECT TOP 1 *
FROM Temp
ORDER BY Id;
I am trying out my hands on oracle 11g. I have a requirement such that I want to fetch those id from list which does not exists in table.
For example:
SELECT * FROM STOCK
where item_id in ('1','2'); // Return those records where result is null
I mean if item_id '1' is not present in db then the query should return me 1.
How can I achieve this?
You need to store the values in some sort of "table". Then you can use left join or not exists or something similar:
with ids as (
select 1 as id from dual union all
select 2 from dual
)
select ids.id
from ids
where not exists (select 1 from stock s where s.item_id = ids.id);
You can use a LEFT JOIN to an in-line table that contains the values to be searched:
SELECT t1.val
FROM (
SELECT '1' val UNION ALL SELECT '2'
) t1
LEFT JOIN STOCK t2 ON t1.val = t2.item_id
WHERE t2.item_id IS NULL
First create the list of possible IDs (e.g. 0 to 99 in below query). You can use a recursive cte for this. Then select these IDs and remove the IDs already present in the table from the result:
with possible_ids(id) as
(
select 0 as id from dual
union all
select id + 1 as id from possible_ids where id < 99
)
select id from possible_ids
minus
select item_id from stock;
A primary concern of the OP seems to be a terse notation of the query, notably the set of values to test for. The straightforwwrd recommendation would be to retrieve these values by another query or to generate them as a union of queries from the dual table (see the other answers for this).
The following alternative solution allows for a verbatim specification of the test values under the following conditions:
There is a character that does not occur in any of the test values provided ( in the example that will be - )
The number of values to test stays well below 2000 (to be precise, the list of values plus separators must be written as a varchar2 literal, which imposes the length limit ). However, this should not be an actual concern - If the test involves lists of hundreds of ids, these lists should definitely be retrieved froma table/view.
Caveat
Whether this method is worth the hassle ( not to mention potential performance impacts ) is questionable, imho.
Solution
The test values will be provided as a single varchar2 literal with - separating the values which is as terse as the specification as a list argument to the IN operator. The string starts and ends with -.
'-1-2-3-156-489-4654648-'
The number of items is computed as follows:
select cond, regexp_count ( cond, '[-]' ) - 1 cnt_items from (select '-1-2-3-156-489-4654648-' cond from dual)
A list of integers up to the number of items starting with 1 can be generated using the LEVEL pseudocolumn from hierarchical queries:
select level from dual connect by level < 42;
The n-th integer from that list will serve to extract the n-th value from the string (exemplified for the 4th value) :
select substr ( cond, instr(cond,'-', 1, 4 )+1, instr(cond,'-', 1, 4+1 ) - instr(cond,'-', 1, 4 ) - 1 ) si from (select cond, regexp_count ( cond, '[-]' ) - 1 cnt_items from (select '-1-2-3-156-489-4654648-' cond from dual) );
The non-existent stock ids are generated by subtracting the set of stock ids from the set of values. Putting it all together:
select substr ( cond, instr(cond,'-',1,level )+1, instr(cond,'-',1,level+1 ) - instr(cond,'-',1,level ) - 1 ) si
from (
select cond
, regexp_count ( cond, '[-]' ) - 1 cnt_items
from (
select '-1-2-3-156-489-4654648-' cond from dual
)
)
connect by level <= cnt_items + 1
minus
select item_id from stock
;
can anybody explain me why i get invalid identifier error and why cannot be variable z.cupu reachable?
ORA-00904: "Z"."CUPU": invalid identifier
select
(select listagg(text, ', ') within group (order by kod)
from cis_chyby_pu_na_uss
where kod in (
select
regexp_substr(t.stav_full, '[^,]+', 1, l.lev) split
from PREKLAPANIE_PU_NA_USS_HIST t, (select rownum as lev
from dual
connect by level <= length (trim(regexp_replace((select stav_full
from PREKLAPANIE_PU_NA_USS_HIST h
where z.cupu = h.cislo_pu)
------------------------------------------------------------------------------------------------------------------^
, '[^,]+')))
) l
where t.cislo_pu = z.cupu
and z.stav <> 100)
)
from zz_2202 z
with tab as
(select 1 n from dual)
select * from tab root
where n in (select child1.n from tab child1
where child1.n in (select child2.n from tab child2
where child2.n = root.n));
OK
with tab as
(select 1 n from dual)
select (select * from tab child1 where child1.n = root.n)
from tab root;
OK
with tab as
(select 1 n from dual)
select (select * from (select * from tab child2 where child2.n = root.n))
from tab root;
ERROR
So there is a limit for nesting in the select list which seems to be equal to 1.
Oracle performs a correlated subquery when a nested subquery
references a column from a table referred to a parent statement one
level above the subquery. The parent statement can be a SELECT,
UPDATE, or DELETE statement in which the subquery is nested. A
correlated subquery conceptually is evaluated once for each row
processed by the parent statement. However, the optimizer may choose
to rewrite the query as a join or use some other technique to
formulate a query that is semantically equivalent. Oracle resolves
unqualified columns in the subquery by looking in the tables named in
the subquery and then in the tables named in the parent statement.
i am using Microsoft SQL Server 2008
i would like to save the result of a subquery to reuse it in a following subquery.
Is this possible?
What is best practice to do this? (I am very new to SQL)
My query looks like:
INSERT INTO [dbo].[TestTable]
(
[a]
,[b]
)
SELECT
(
SELECT TOP 1 MAT_WS_ID
FROM #TempTableX AS X_ALIAS
WHERE OUTERBASETABLE.LT_ALL_MATERIAL = X_ALIAS.MAT_RM_NAME
)
,(
SELECT TOP 1 MAT_WS_NAME
FROM #TempTableY AS Y_ALIAS
WHERE Y_ALIAS.MAT_WS_ID = MAT_WS_ID
--(
--SELECT TOP 1 MAT_WS_ID
--FROM #TempTableX AS X_ALIAS
--WHERE OUTERBASETABLE.LT_ALL_MATERIAL = X_ALIAS.MAT_RM_NAME
--)
)
FROM [dbo].[LASERTECHNO] AS OUTERBASETABLE
My question is:
Is this correct what i did.
I replaced the second SELECT Statement in the WHERE-Clause for [b] (which is commented out and exactly the same as for [a]), with the result of the first SELECT Statement of [a] (=MAT_WS_ID).
It seems to give the right results.
But i dont understand why!
I mean MAT_WS_ID is part of both temporary tables X_ALIAS and Y_ALIAS.
So in the SELECT statement for [b], in the scope of the [b]-select-query, MAT_WS_ID could only be known from the Y_ALIAS table. (Or am i wrong, i am more a C++, maybe the scope things in SQL and C++ are totally different)
I just wannt to know what is the best way in SQL Server to reuse an scalar select result.
Or should i just dont care and copy the select for every column and the sql server optimizes it by its own?
One approach would be outer apply:
SELECT mat.MAT_WS_ID
, (
SELECT TOP 1 MAT_WS_NAME
FROM #TempTableY AS Y_ALIAS
WHERE Y_ALIAS.MAT_WS_ID = mat.MAT_WS_ID
)
FROM [dbo].[LASERTECHNO] AS OUTERBASETABLE
OUTER APPLY
(
SELECT TOP 1 MAT_WS_ID
FROM #TempTableX AS X_ALIAS
WHERE OUTERBASETABLE.LT_ALL_MATERIAL = X_ALIAS.MAT_RM_NAME
) as mat
You could rank rows in #TempTableX and #TempTableY partitioning them by MAT_RM_NAME in the former and by MAT_WS_ID in the latter, then use normal joins with filtering by rownum = 1 in both tables (rownum being the column containing the ranking numbers in each of the two tables):
WITH x_ranked AS (
SELECT
*,
rownum = ROW_NUMBER() OVER (PARTITION BY MAT_RM_NAME ORDER BY (SELECT 1))
FROM #TempTableX
),
y_ranked AS (
SELECT
*,
rownum = ROW_NUMBER() OVER (PARTITION BY MAT_WS_ID ORDER BY (SELECT 1))
FROM #TempTableY
)
INSERT INTO dbo.TestTable (a, b)
SELECT
x.MAT_WS_ID,
y.MAT_WS_NAME
FROM dbo.LASERTECHNO t
LEFT JOIN x_ranked x ON t.LT_ALL_MATERIAL = x.MAT_RM_NAME AND x.rownum = 1
LEFT JOIN y_ranked y ON x.MAT_WS_ID = y.MAT_WS_ID AND y.rownum = 1
;
The ORDER BY (SELECT 1) bit is a trick to specify an indeterminate ordering, which, accordingly, would result in indeterminate rownum = 1 rows picked by the query. That is to more or less duplicate your TOP 1 without an explicit order, but I would recommend you to specify a more sensible ORDER BY clause to make the results more predictable.