feat(isthmus): mapping of string extract and pad fns (#619)

Author: asuriy

isthmus/src/main/java/io/substrait/isthmus/expression/FunctionMappings.java

@@ -93,7 +93,11 @@ public class FunctionMappings {
               s(SqlLibraryOperators.STARTS_WITH, "starts_with"),
               s(SqlLibraryOperators.ENDS_WITH, "ends_with"),
               s(SqlLibraryOperators.CONTAINS_SUBSTR, "contains"),
-              s(SqlStdOperatorTable.POSITION, "strpos"))
+              s(SqlStdOperatorTable.POSITION, "strpos"),
+              s(SqlLibraryOperators.LEFT, "left"),
+              s(SqlLibraryOperators.RIGHT, "right"),
+              s(SqlLibraryOperators.LPAD, "lpad"),
+              s(SqlLibraryOperators.RPAD, "rpad"))
           .build();
 
   public static final ImmutableList<Sig> AGGREGATE_SIGS =

isthmus/src/test/java/io/substrait/isthmus/StringFunctionTest.java

@@ -13,6 +13,8 @@ public final class StringFunctionTest extends PlanTestBase {
   static String CREATES = "CREATE TABLE strings (c16 CHAR(16), vc32 VARCHAR(32), vc VARCHAR)";
   static String REPLACE_CREATES =
       "CREATE TABLE replace_strings (c16 CHAR(16), vc32 VARCHAR(32), replace_from VARCHAR(16), replace_to VARCHAR(16))";
+  static String CHAR_INT_CREATES =
+      "CREATE TABLE int_num_strings (vc32 VARCHAR(32), vc VARCHAR, i32 INT)";
 
   @ParameterizedTest
   @ValueSource(strings = {"c16", "vc32"})
@@ -270,4 +272,42 @@ void testStrposWithLiteral(String left, String right) throws Exception {
 
     assertSqlRoundTrip(query);
   }
+
+  @ParameterizedTest
+  @CsvSource({"vc32, i32", "vc, i32"})
+  void testLeft(String left, String right) throws Exception {
+
+    String query = String.format("SELECT LEFT(%s, %s) FROM int_num_strings", left, right);
+
+    assertSqlSubstraitRelRoundTrip(query, CHAR_INT_CREATES);
+  }
+
+  @ParameterizedTest
+  @CsvSource({"vc32, i32", "vc, i32"})
+  void testRight(String left, String right) throws Exception {
+
+    String query = String.format("SELECT RIGHT(%s, %s) FROM int_num_strings", left, right);
+
+    assertSqlSubstraitRelRoundTrip(query, CHAR_INT_CREATES);
+  }
+
+  @ParameterizedTest
+  @CsvSource({"vc32, i32, vc32", "vc, i32, vc"})
+  void testRpad(String left, String center, String right) throws Exception {
+
+    String query =
+        String.format("SELECT RPAD(%s, %s, %s) FROM int_num_strings", left, center, right);
+
+    assertSqlSubstraitRelRoundTrip(query, CHAR_INT_CREATES);
+  }
+
+  @ParameterizedTest
+  @CsvSource({"vc32, i32, vc32", "vc, i32, vc"})
+  void testLpad(String left, String center, String right) throws Exception {
+
+    String query =
+        String.format("SELECT LPAD(%s, %s, %s) FROM int_num_strings", left, center, right);
+
+    assertSqlSubstraitRelRoundTrip(query, CHAR_INT_CREATES);
+  }
 }