BUG: read_sql wraps plain SQL strings in sqlalchemy.text() to allow % modulo and LIKE patterns (#35484)

pandas/io/sql.py

@@ -94,6 +94,15 @@
 # -- Helper functions
 
 
+def _sa_text_if_string(stmt):
+    """Wrap plain SQL strings in sqlalchemy.text()."""
+    try:
+        import sqlalchemy as sa
+    except Exception:
+        return stmt
+    return sa.text(stmt) if isinstance(stmt, str) else stmt
+
+
 def _process_parse_dates_argument(parse_dates):
     """Process parse_dates argument for read_sql functions"""
     # handle non-list entries for parse_dates gracefully
@@ -1848,7 +1857,9 @@ def read_query(
         read_sql_table : Read SQL database table into a DataFrame.
         read_sql
 
+
         """
+        sql = _sa_text_if_string(sql)
         result = self.execute(sql, params)
         columns = result.keys()
 

pandas/tests/io/sql/test_percent_patterns.py

@@ -0,0 +1,45 @@
+# pandas/tests/io/sql/test_percent_patterns.py
+import os
+
+import pytest
+
+sa = pytest.importorskip("sqlalchemy")
+
+PG = os.environ.get("PANDAS_TEST_POSTGRES_URI")
+URL = PG or "sqlite+pysqlite:///:memory:"
+
+
+def _eng():
+    return sa.create_engine(URL)
+
+
+def test_text_modulo():
+    import pandas as pd
+
+    with _eng().connect() as c:
+        df = pd.read_sql(sa.text("SELECT 5 % 2 AS r"), c)
+    assert df.iloc[0, 0] == 1
+
+
+def test_like_single_percent():
+    import pandas as pd
+
+    with _eng().connect() as c:
+        df = pd.read_sql(
+            sa.text("SELECT 'John' AS fullname WHERE 'John' LIKE 'John%'"),
+            c,
+        )
+    assert len(df) == 1
+
+
+def test_sqlalchemy_expr_percent_operator():
+    from sqlalchemy import (
+        literal,
+        select,
+    )
+
+    import pandas as pd
+
+    with _eng().connect() as c:
+        df = pd.read_sql(select((literal(7) % literal(3)).label("r")), c)
+    assert df.iloc[0, 0] == 1