properly handle non-string field

Signed-off-by: Jialiang Liang <jiallian@amazon.com>

Author: RyanL1997

core/src/main/java/org/opensearch/sql/calcite/CalciteRelNodeVisitor.java

@@ -48,6 +48,7 @@
 import org.apache.calcite.rex.RexNode;
 import org.apache.calcite.rex.RexWindowBounds;
 import org.apache.calcite.sql.fun.SqlStdOperatorTable;
+import org.apache.calcite.sql.type.SqlTypeFamily;
 import org.apache.calcite.sql.type.SqlTypeName;
 import org.apache.calcite.tools.RelBuilder;
 import org.apache.calcite.tools.RelBuilder.AggCall;
@@ -182,6 +183,13 @@ public RelNode visitRegex(Regex node, CalcitePlanContext context) {
     RexNode fieldRex = rexVisitor.analyze(node.getField(), context);
     RexNode patternRex = rexVisitor.analyze(node.getPattern(), context);
 
+    if (!SqlTypeFamily.CHARACTER.contains(fieldRex.getType())) {
+      throw new IllegalArgumentException(
+          String.format(
+              "Regex command requires field of string type, but got %s for field '%s'",
+              fieldRex.getType().getSqlTypeName(), node.getField().toString()));
+    }
+
     RexNode regexCondition =
         context.rexBuilder.makeCall(
             org.apache.calcite.sql.fun.SqlLibraryOperators.REGEXP_CONTAINS, fieldRex, patternRex);

ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLRegexTest.java

@@ -5,6 +5,9 @@
 
 package org.opensearch.sql.ppl.calcite;
 
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
 import org.apache.calcite.rel.RelNode;
 import org.apache.calcite.test.CalciteAssert;
 import org.junit.Test;
@@ -154,19 +157,16 @@ public void testRegexCaseInsensitive() {
   }
 
   @Test
-  public void testRegexWithNumericPattern() {
-    String ppl = "source=EMP | regex SAL='[0-9]{4,}' | fields ENAME, SAL";
-    RelNode root = getRelNode(ppl);
-    String expectedLogical =
-        "LogicalProject(ENAME=[$1], SAL=[$5])\n"
-            + "  LogicalFilter(condition=[REGEXP_CONTAINS($5, '[0-9]{4,}':VARCHAR)])\n"
-            + "    LogicalTableScan(table=[[scott, EMP]])\n";
-    verifyLogical(root, expectedLogical);
-
-    String expectedSparkSql =
-        "SELECT `ENAME`, `SAL`\n"
-            + "FROM `scott`.`EMP`\n"
-            + "WHERE REGEXP_CONTAINS(`SAL`, '[0-9]{4,}')";
-    verifyPPLToSparkSQL(root, expectedSparkSql);
+  public void testRegexWithNonStringFieldThrowsException() {
+    String ppl = "source=EMP | regex EMPNO='123.*'";
+    try {
+      getRelNode(ppl);
+      fail("Expected IllegalArgumentException for non-string field type");
+    } catch (IllegalArgumentException e) {
+      assertTrue(
+          "Expected error message about field type",
+          e.getMessage().contains("Regex command requires field of string type"));
+      assertTrue("Expected error message to mention field name", e.getMessage().contains("EMPNO"));
+    }
   }
 }