UNION ALL in CTE
-
19-04-2021 - |
Question
I'm trying to get a UNION ALL working with a CTE which I'm using for paging. I need to get all records matching a set of criteria from two tables, then page the results. The first table's CTE looks like this:
;WITH Results_CTE AS (SELECT t1.SomeIntKey1, ROW_NUMBER() OVER (ORDER BY SomeIntKey1) AS RowNum
FROM Table1 t1
LEFT JOIN CalculatedData d ON d.Key = t1.SomeIntKey1
WHERE Postcode LIKE 'CHX 1XX%'
) SELECT * FROM Results_CTE a INNER JOIN CalclatedData d ON a.SomeIntKey1 = d.Key WHERE RowNum >= 0 AND RowNum <= 10 OPTION(RECOMPILE)
The second table's paging SQL (which works fine) is:
;WITH Results_CTE AS (SELECT t2.SomeIntKey2, ROW_NUMBER() OVER (ORDER BY SomeIntKey2) AS RowNum
FROM Table2 t2
LEFT JOIN CalculatedData d ON d.Key = t1.SomeIntKey2
WHERE Postcode LIKE 'CHX 1XX%'
) SELECT * FROM Results_CTE a INNER JOIN CalclatedData d ON a.SomeIntKey2 = d.Key WHERE RowNum >= 0 AND RowNum <= 10 OPTION(RECOMPILE)
For the combined paged data, I've tried something like:
;WITH Results_CTE AS (SELECT t2.SomeIntKey2, ROW_NUMBER() OVER (ORDER BY SomeIntKey2) AS RowNum
FROM Table2 t2
LEFT JOIN CalculatedData d ON d.Key = t1.SomeIntKey2
WHERE Postcode LIKE 'CHX 1XX%'
UNION ALL
SELECT t1.SomeIntKey1
FROM Table1 t1
LEFT JOIN CalculatedData d ON d.Key = t1.SomeIntKey1
WHERE Postcode LIKE 'CHX 1XX%'
) SELECT * FROM Results_CTE a INNER JOIN CalclatedData d ON a.SomeIntKey2 = d.Key WHERE RowNum >= 0 AND RowNum <= 10 OPTION(RECOMPILE)
However, this results in an error:
All queries combined using a UNION, INTERSECT or EXCEPT operator must have an equal number of expressions in their target lists.
I know UNION ALLs can be confusing at the best of times, especially with joins, but I'm essentially getting a list of INT keys from two tables, then joining them to a third which contains the data I need (keys from both tables will be present in the joined column on the Data
table.
La solution
You need to make sure that both result sets have the same columns:
WITH Results_CTE AS
(
SELECT
t2.SomeIntKey2 as Key,
ROW_NUMBER() OVER (ORDER BY SomeIntKey2) AS RowNum
FROM
Table2 t2
LEFT JOIN CalculatedData d
ON d.Key = t1.SomeIntKey2
WHERE Postcode LIKE 'CHX 1XX%'
UNION ALL
SELECT
t1.SomeIntKey1 as Key,
0 as RowNum
FROM
Table1 t1
LEFT JOIN CalculatedData d
ON d.Key = t1.SomeIntKey1
WHERE Postcode LIKE 'CHX 1XX%'
)
SELECT * FROM Results_CTE a INNER JOIN CalclatedData d ON a.SomeIntKey2 = d.Key
WHERE RowNum >= 0 AND RowNum <= 10 OPTION(RECOMPILE)
Please note that the second part of the UNION ALL
now always returns 0 for the RowNum. If you want to have the RowNum column for the result of the UNION ALL
you need another sub query:
WITH Results_CTE AS
(
SELECT
s.Key,
ROW_NUMBER() OVER (ORDER BY s.Key) AS RowNum
FROM
(
SELECT
t2.SomeIntKey2 as Key,
FROM
Table2 t2
LEFT JOIN CalculatedData d
ON d.Key = t1.SomeIntKey2
WHERE Postcode LIKE 'CHX 1XX%'
UNION ALL
SELECT
t1.SomeIntKey1 as Key
FROM
Table1 t1
LEFT JOIN CalculatedData d
ON d.Key = t1.SomeIntKey1
WHERE Postcode LIKE 'CHX 1XX%'
)
)
SELECT * FROM Results_CTE a INNER JOIN CalclatedData d ON a.SomeIntKey2 = d.Key
WHERE RowNum >= 0 AND RowNum <= 10 OPTION(RECOMPILE)
Autres conseils
Your second SELECT in the your UNION ALL doesn't return the same number of columns, hence the problem.
Try:
;WITH Results_CTE AS (
SELECT IntKey, ROW_NUMBER() OVER (ORDER BY IntKey) AS RowNum
FROM
(
SELECT t2.SomeIntKey2 AS IntKey
FROM Table2 t2
LEFT JOIN CalculatedData d ON d.Key = t1.SomeIntKey2
WHERE Postcode LIKE 'CHX 1XX%'
UNION ALL
SELECT t1.SomeIntKey1 AS IntKey
FROM Table1 t1
LEFT JOIN CalculatedData d ON d.Key = t1.SomeIntKey1
WHERE Postcode LIKE 'CHX 1XX%'
) t
)
SELECT * FROM Results_CTE a INNER JOIN CalclatedData d ON a.IntKey = d.Key