SQL Server CTE doesn't Join Properly - sql

Question

The data for this project contains two columns with semicolon-delimited strings. These are actually ordered pairs. So, for example, in: "a;b;c", "x;y;z", 'a' is paired with 'x'. The goal for our query is to create a table where this relationship is clearly represented one row at a time.
Here is a script to re-create the sample data:
DROP TABLE IF EXISTS dbo.sampleData;
DROP TABLE IF EXISTS dbo.lookupCPT;
GO
CREATE TABLE sampleData
(
numRow bigint IDENTITY(1,1) NOT NULL CONSTRAINT PK_numRow PRIMARY KEY,
sDelimQty varchar(MAX) NULL,
sDelimCPT varchar(MAX) NULL
)
CREATE TABLE lookupCPT
(
numRow bigint IDENTITY(1,1) NOT NULL CONSTRAINT PK_numRowCPT PRIMARY KEY,
sCPTCode varchar(10) NULL,
decCPTRate decimal(16,2) NULL
)
INSERT [dbo].[lookupCPT] ([numRow], [sCPTCode], [decCPTRate])
VALUES (1, N'123', CAST(4.00 AS Decimal(16, 2)))
INSERT [dbo].[lookupCPT] ([numRow], [sCPTCode], [decCPTRate])
VALUES (2, N'456', CAST(5.00 AS Decimal(16, 2)))
INSERT [dbo].[lookupCPT] ([numRow], [sCPTCode], [decCPTRate])
VALUES (3, N'789', CAST(7.00 AS Decimal(16, 2)))
INSERT [dbo].[sampleData] ([numRow], [sDelimQty], [sDelimCPT])
VALUES (1, N'1;2', N'123;789')
INSERT [dbo].[sampleData] ([numRow], [sDelimQty], [sDelimCPT])
VALUES (2, N'3', N'456')
We attempted to accomplish this using common table expressions:
WITH Qty_CTE (numRowQ, Qty) AS
(
SELECT numRow, value
FROM sampleData
CROSS APPLY STRING_SPLIT(sDelimQty, ';')
),
CPT_CTE (numRowC, CPT) AS
(
SELECT numRow, value
FROM sampleData
CROSS APPLY STRING_SPLIT(sDelimCPT, ';')
)
SELECT *
FROM sampleData
JOIN CPT_CTE c on c.numRowC = sampleData.numRow
JOIN Qty_CTE q on q.numRowQ = sampleData.numRow
However, doing this doubles the amount of rows in our output:
q1
But, if we remove either one of the two joins, it returns correctly:
q2
Any ideas? Thanks very much
After all the helpful answers, below is the final solution. Cheers!
WITH Qty_CTE (numRowQ, Qty, RN) AS
(
SELECT
numRow, value,
ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS RN
FROM
sampleData
CROSS APPLY
STRING_SPLIT(sDelimQty, ';')
),
CPT_CTE (numRowC, CPT, CPTRate, RN) AS
(
SELECT
s.numRow, value as CPT, l.decCPTRate as CPTRate,
ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS RN
FROM
sampleData s
CROSS APPLY
STRING_SPLIT(sDelimCPT, ';')
JOIN
lookupCPT l ON value = l.sCPTCode
)
SELECT
numRow, sDelimCPT, sDelimQty, CPT, CPTRate, Qty, CPTRate * Qty as Total
FROM
sampleData
JOIN
CPT_CTE c on c.numRowC = sampleData.numRow
JOIN
Qty_CTE q on q.numRowQ = sampleData.numRow AND c.RN = q.RN

Answer 1

If your STRING_SPLIT function preserve order, then this will work.
WITH Qty_CTE (numRowQ, Qty, RN) AS
(
SELECT numRow, value, ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS RN
FROM sampleData
CROSS APPLY STRING_SPLIT(sDelimQty, ';')
),
CPT_CTE (numRowC, CPT, RN) AS
(
SELECT numRow, value, ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS RN
FROM sampleData
CROSS APPLY STRING_SPLIT(sDelimCPT, ';')
)
SELECT * FROM sampleData
JOIN CPT_CTE c on c.numRowC = sampleData.numRow
JOIN Qty_CTE q on q.numRowQ = sampleData.numRow AND c.RN = q.RN

Answer 2

Both your examples q1 and q2 work as expected. Qty_CTE has a cardinality of 3 (Record 1 appears twice, record 2 appears once), so does CPT_CTE.
sampleData has a cardinality of 2 (each row appears once only)
Since you're joining on the PK, sampleData x Qty_CTE x CPT_CTE should return 5 records, which it does (1x2x2 records for numrow 1 and 1x1x1 record for numrow 2). If you remove either Qty_CTE or CPT_CTE it should return 3 records, which it does (1x1x1 record for numrow 2 and 1x2 records for numrow 1).
We could propose a solution based on an expected result, if you had one.