Use same parameter multiple times in sql query

Question

I am using pyodbc and Microsoft SQL Server

I am trying to replicate a stored procedure in python where this query is executed for every @currentSurveyId

SELECT *
                FROM
                (
                    SELECT
                        SurveyId,
                        QuestionId,
                        1 as InSurvey
                    FROM
                        SurveyStructure
                    WHERE
                        SurveyId = @currentSurveyId
                    UNION
                    SELECT 
                        @currentSurveyId as SurveyId,
                        Q.QuestionId,
                        0 as InSurvey
                    FROM
                        Question as Q
                    WHERE NOT EXISTS
                    (
                        SELECT *
                        FROM SurveyStructure as S
                        WHERE S.SurveyId = @currentSurveyId AND S.QuestionId = Q.QuestionId
                    )
                ) as t
                ORDER BY QuestionId

In Python, I so far have:

cursor.execute("""SELECT UserId FROM dbo.[User]""")
allSurveyID = cursor.fetchall()

for i in allSurveyID:
    p = i
    test = cursor.execute("""SELECT *
                FROM
                (
                    SELECT
                        SurveyId,
                        QuestionId,
                        1 as InSurvey
                    FROM
                        SurveyStructure
                    WHERE
                        SurveyId = (?)
                    UNION
                    SELECT 
                        (?) as SurveyId,
                        Q.QuestionId,
                        0 as InSurvey
                    FROM
                        Question as Q
                    WHERE NOT EXISTS
                    (
                        SELECT *
                        FROM SurveyStructure as S
                        WHERE S.SurveyId = (?)AND S.QuestionId = Q.QuestionId
                    )
                ) as t
                ORDER BY QuestionId""",p)

for i in test:
    print(i)

The parameter works when used once (if I delete everything from UNION onwards). When trying to use the same parameter in the rest of the query, I get the following error:('The SQL contains 3 parameter markers, but 1 parameters were supplied', 'HY000')

Is it possible to use the same parameter multiple times in the same query?

Thank you

Gord Thompson · Accepted Answer · 2022-05-22 18:43:24Z

1

pyodbc itself only supports "qmark" (positional) parameters (ref: here), but with T-SQL (Microsoft SQL Server) we can use an anonymous code block to avoid having to pass the same parameter value multiple times:

cnxn = pyodbc.connect(connection_string)
crsr = cnxn.cursor()

sql = """\
SET NOCOUNT ON;
DECLARE @my_param int = ?;
SELECT @my_param AS original, @my_param * 2 AS doubled;
"""
results = crsr.execute(sql, 2).fetchone()
print(results)  # (2, 4)

edited May 22, 2022 at 18:43

answered May 22, 2022 at 18:33

Gord Thompson

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Comments

Parfait · Accepted Answer · 2022-05-22 21:45:16Z

If reusing the same parameter value, simply multiply a one-item list of the parameter:

cursor.execute(sql, [p]*3)

Consider also refactoring your SQL for LEFT JOIN (or FULL JOIN) requiring two qmarks:

SELECT DISTINCT
       ISNULL(S.SurveyId, ?) AS SurveyId, 
       Q.QuestionId, 
       IIF(S.SurveyId IS NOT NULL, 1, 0) AS InSurvey 
FROM Question Q
LEFT JOIN SurveyStructure S
  ON S.QuestionId = Q.QuestionId 
  AND S.SurveyId = ?
ORDER BY Q.QuestionId

Possibly even for one parameter:

SELECT MAX(S.SurveyId) AS SurveyId, 
       Q.QuestionId, 
       IIF(S.SurveyId IS NOT NULL, 1, 0) AS InSurvey 
FROM Question Q
LEFT JOIN SurveyStructure S
  ON S.QuestionId = Q.QuestionId 
  AND S.SurveyId = ?
GROUP BY Q.QuestionId, 
         IIF(S.SurveyId IS NOT NULL, 1, 0)
ORDER BY Q.QuestionId

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