I have an SQLite database with three columns, and I'm trying to use parameter substitution for tuples to SELECT rows. This is my table:
conn = sqlite3.connect("SomeDb.sqlite3")
conn.execute("""
CREATE TABLE RoadSegmentDistribution(
Source INTEGER,
Destination INTEGER,
Distribution TEXT
)
""")
I know how to substitute with non-tuples, but I cannot figure out how to do it with tuples.
Based on this answer, I thought I simply had to substitute each and every value across the list of tuples:
for e in conn.execute("""
SELECT *
FROM RoadSegmentDistribution
WHERE (
Source, Destination
) IN (VALUES (?,?), (?,?), (?,?), (?,?), (?,?))
""",
[(1, 2),(2, 3),(4, 5),(6, 7),(8, 9)]
):
print(e)
but then I get the error
ProgrammingError: Incorrect number of bindings supplied. The current statement uses 10, and there are 5 supplied.
Obviously this means that I only need one question mark per tuple, right?:
for e in conn.execute("""
SELECT *
FROM RoadSegmentDistribution
WHERE (
Source, Destination
) IN (VALUES (?), (?), (?), (?), (?))
""",
[(1, 2),(2, 3),(4, 5),(6, 7),(8, 9)]
):
print(e)
But then I get this error:
OperationalError: sub-select returns 1 columns - expected 2
I cannot insert the values manually like in the linked answer, since I don't know what the list parameter contains. This means that I need to do some kind of ",".join() based on the length of the list, but I'll figure that out once I know how to do substitution with a fixed-length list.
How would I do this?
Using the str.join method is indeed a good way to achieve this, given the lack of native support for container-based placeholders in SQL engines:
values = [(1, 2), (2, 3), (4, 5), (6, 7), (8, 9)]
for e in conn.execute(f"""
SELECT *
FROM RoadSegmentDistribution
WHERE (
Source, Destination
) IN (VALUES {','.join(f'({",".join("?" * len(t))})' for t in values)})
""",
[i for t in values for i in t]
):
print(e)
where, with the given values:
f"""
SELECT *
FROM RoadSegmentDistribution
WHERE (
Source, Destination
) IN (VALUES {','.join(f'({",".join("?" * len(t))})' for t in values)})
"""
would expand into:
SELECT *
FROM RoadSegmentDistribution
WHERE (
Source, Destination
) IN (VALUES (?,?),(?,?),(?,?),(?,?),(?,?))