Cast CTAS output to Iceberg storage types#1088
Merged
Merged
Conversation
Member
|
Thanks! |
Contributor
Author
|
As an aside, should I start targeting main with my prs? |
NiclasHaderer
added a commit
to motherduckdb/duckdb-iceberg
that referenced
this pull request
Jun 23, 2026
Merged
NiclasHaderer
added a commit
to motherduckdb/duckdb-iceberg
that referenced
this pull request
Jun 25, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
CTAS derives its columns from the SELECT output types, but the table (and its write pipeline) is created with the Iceberg storage types. These differ for types that have no Iceberg equivalent (e.g. HUGEINT).
The CTAS write appends the SELECT chunks straight into a ColumnDataCollection typed with the storage types, so the types disagree (HUGEINT vs DECIMAL(38,0)). This trips D_ASSERT(types == input_types) in assertion builds; in release it is masked only because HUGEINT and DECIMAL(38,0) share the INT128 layout.
Fix:
Insert a projection above the CTAS plan that casts each column to its Iceberg storage type before the write. The storage types come from IcebergCreateTableRequest::CreateIcebergSchema (the same source the table is created from), and the cast reuses BoundCastExpression::AddCastToType so nested types are handled recursively. The projection is skipped when no column needs a cast.