From 82771ab5a185a4ec5ef54dd69469773a7f7caf62 Mon Sep 17 00:00:00 2001
From: Hin Tse <5867507+hintse@users.noreply.github.com>
Date: Tue, 25 Aug 2026 04:20:10 -0400
Subject: [PATCH 1/2] Map char stripping expressions to SQL.

Signed-off-by: Hin Tse <5867507+hintse@users.noreply.github.com>
---
 polars_io_tools/io_sources/sql_utils.py       |  6 ++++++
 polars_io_tools/tests/io_sources/test_base.py | 14 ++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/polars_io_tools/io_sources/sql_utils.py b/polars_io_tools/io_sources/sql_utils.py
index 74051a1..07b5922 100644
--- a/polars_io_tools/io_sources/sql_utils.py
+++ b/polars_io_tools/io_sources/sql_utils.py
@@ -296,6 +296,12 @@ 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")
         else:
             log.warning(f"Unsupported string function: {node.function_type}")
             self.result = None
diff --git a/polars_io_tools/tests/io_sources/test_base.py b/polars_io_tools/tests/io_sources/test_base.py
index 70152d8..df34156 100644
--- a/polars_io_tools/tests/io_sources/test_base.py
+++ b/polars_io_tools/tests/io_sources/test_base.py
@@ -1088,6 +1088,20 @@ 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_fill_null_predicates(tester):
     for val in [0, 1, 9]:
         expr = pl.col("nullable").fill_null(val) > 5

From c5b80d6a66a881192cffc648f5388c1669cab601 Mon Sep 17 00:00:00 2001
From: Hin Tse <5867507+hintse@users.noreply.github.com>
Date: Tue, 25 Aug 2026 04:24:50 -0400
Subject: [PATCH 2/2] Map string concat expression to SQL.

Signed-off-by: Hin Tse <5867507+hintse@users.noreply.github.com>
---
 polars_io_tools/io_sources/sql_utils.py       |  2 ++
 polars_io_tools/tests/io_sources/test_base.py | 10 ++++++++++
 2 files changed, 12 insertions(+)

diff --git a/polars_io_tools/io_sources/sql_utils.py b/polars_io_tools/io_sources/sql_utils.py
index 07b5922..50dec87 100644
--- a/polars_io_tools/io_sources/sql_utils.py
+++ b/polars_io_tools/io_sources/sql_utils.py
@@ -302,6 +302,8 @@ def _handle_string_function(self, node: FunctionNode, input_exprs: list[sqlglot.
             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
diff --git a/polars_io_tools/tests/io_sources/test_base.py b/polars_io_tools/tests/io_sources/test_base.py
index df34156..7ba0a40 100644
--- a/polars_io_tools/tests/io_sources/test_base.py
+++ b/polars_io_tools/tests/io_sources/test_base.py
@@ -1102,6 +1102,16 @@ def test_strip_chars_predicate_pushed_down():
         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