Casting of literals is done by Calcite, except for strings (#178)

* Casting of literals is done by Calcite, except for strings

* Added more tests for simple cases

Author: nils-braun

dask_sql/physical/rex/core/call.py

@@ -188,6 +188,9 @@ def __init__(self):
         super().__init__(self.cast)
 
     def cast(self, operand, rex=None) -> SeriesOrScalar:
+        if not is_frame(operand):
+            return operand
+
         output_type = str(rex.getType())
         output_type = sql_to_python_type(output_type.upper())
 

tests/integration/test_filter.py

@@ -59,3 +59,12 @@ def test_filter_with_nan(c):
     assert_frame_equal(
         return_df, expected_df,
     )
+
+
+def test_string_filter(c, string_table):
+    return_df = c.sql("SELECT * FROM string_table WHERE a = 'a normal string'")
+    return_df = return_df.compute()
+
+    assert_frame_equal(
+        return_df, string_table.head(1),
+    )

tests/integration/test_sqlite.py

@@ -111,6 +111,27 @@ def test_groupby(assert_query_gives_same_result):
     """
     )
 
+    assert_query_gives_same_result(
+        """
+        SELECT AVG(c)
+        FROM df2
+    """
+    )
+
+
+def test_calc(assert_query_gives_same_result):
+    assert_query_gives_same_result(
+        """
+        SELECT
+            a + b,
+            a*b,
+            a*5,
+            a / user_id,
+            user_id / a
+        FROM df1
+    """
+    )
+
 
 def test_filter(assert_query_gives_same_result):
     assert_query_gives_same_result(
@@ -132,3 +153,43 @@ def test_filter(assert_query_gives_same_result):
             d NOT LIKE '%c'
     """
     )
+
+    assert_query_gives_same_result(
+        """
+        SELECT
+            d
+        FROM df2
+        WHERE
+            d = 'a'
+    """
+    )
+
+    assert_query_gives_same_result(
+        """
+        SELECT
+            *
+        FROM df1
+        WHERE
+            1 < a AND a < 5
+    """
+    )
+
+    assert_query_gives_same_result(
+        """
+        SELECT
+            *
+        FROM df1
+        WHERE
+            a < 5 AND b < 5
+    """
+    )
+
+    assert_query_gives_same_result(
+        """
+        SELECT
+            *
+        FROM df1
+        WHERE
+            a + b > 5
+    """
+    )