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Map char stripping and concatenate expressions to SQL. #21

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Merged
ptomecek merged 2 commits into from
Aug 25, 2026
Merged

Map char stripping and concatenate expressions to SQL. #21

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82771ab
Map char stripping expressions to SQL.
hintse Aug 25, 2026
c5b80d6
Map string concat expression to SQL.
hintse Aug 25, 2026
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8 changes: 8 additions & 0 deletions polars_io_tools/io_sources/sql_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -296,6 +296,14 @@ def _handle_string_function(self, node: FunctionNode, input_exprs: list[sqlglot.
self.result = sqlglot.exp.Upper(this=input_exprs[0])
elif node.function_type == StringFunctionType.LOWERCASE:
self.result = sqlglot.exp.Lower(this=input_exprs[0])
elif node.function_type == StringFunctionType.STRIP_CHARS:
self.result = sqlglot.exp.Trim(this=input_exprs[0])
elif node.function_type == StringFunctionType.STRIP_CHARS_START:
self.result = sqlglot.exp.Trim(this=input_exprs[0], position="LEADING")
elif node.function_type == StringFunctionType.STRIP_CHARS_END:
self.result = sqlglot.exp.Trim(this=input_exprs[0], position="TRAILING")
elif node.function_type == StringFunctionType.CONCAT_HORIZONTAL and input_exprs:
self.result = sqlglot.exp.Concat(expressions=input_exprs)
else:
log.warning(f"Unsupported string function: {node.function_type}")
self.result = None
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24 changes: 24 additions & 0 deletions polars_io_tools/tests/io_sources/test_base.py
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Expand Up @@ -1088,6 +1088,30 @@ def test_string_predicates(tester):
tester.assert_predicate_pushed_down(expr3)


def test_strip_chars_predicate_pushed_down():
"""str.strip_chars / str.strip_chars_start / str.strip_chars_end translate to TRIM / LTRIM / RTRIM."""
df = pl.DataFrame({"padded": [" A ", " B ", " C ", " D ", "E"]})
tracker = PredicateTracker(df)

for expr in [
pl.col("padded").str.strip_chars() == "A",
pl.col("padded").str.strip_chars_start() == "A ",
pl.col("padded").str.strip_chars_end() == " A",
]:
tracker.assert_predicate_pushed_down(expr)
tracker.assert_results_match(expr)


def test_concat_horizontal_predicate_pushed_down():
"""pl.concat_str translates to SQL CONCAT(...)."""
df = pl.DataFrame({"first": ["A", "B", "C"], "last": ["X", "Y", "Z"]})
tracker = PredicateTracker(df)

expr = pl.concat_str([pl.col("first"), pl.lit("-"), pl.col("last")]) == "A-X"
tracker.assert_predicate_pushed_down(expr)
tracker.assert_results_match(expr)


def test_fill_null_predicates(tester):
for val in [0, 1, 9]:
expr = pl.col("nullable").fill_null(val) > 5
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