Remove EnhancedCoalesceFunction in favor of built-in Coalesce function (1913/2054)

- numbers are allowed to be coerced to strings

Signed-off-by: Yuanchun Shen <yuanchu@amazon.com>

Author: yuancu

core/src/main/java/org/opensearch/sql/calcite/validate/PplTypeCoercionRule.java

@@ -17,6 +17,31 @@
 import org.apache.calcite.sql.type.SqlTypeCoercionRule;
 import org.apache.calcite.sql.type.SqlTypeName;
 
+/**
+ * Provides PPL-specific type coercion rules that extend Calcite's default type coercion behavior.
+ *
+ * <p>This class defines additional type mapping rules for PPL, particularly for handling custom
+ * types like IP addresses and number-to-string coercion. These additional rules are merged with
+ * Calcite's built-in type coercion rules.
+ *
+ * <p>The additional mappings defined include:
+ *
+ * <ul>
+ *   <li>IP can be coerced to/from string types
+ *   <li>VARCHAR can be coerced from numeric types
+ * </ul>
+ *
+ * <p>Three variants of type coercion rules are provided:
+ *
+ * <ul>
+ *   <li>{@link #instance()} - Standard type coercion rules
+ *   <li>{@link #lenientInstance()} - More permissive type coercion rules
+ *   <li>{@link #assignmentInstance()} - Rules for type assignment validation
+ * </ul>
+ *
+ * @see SqlTypeCoercionRule
+ * @see PplTypeCoercion
+ */
 public class PplTypeCoercionRule {
   /**
    * PPL-specific additional type mapping rules
@@ -25,14 +50,18 @@ public class PplTypeCoercionRule {
    *   <li>IP -> IP
    *   <li>CHARACTER -> IP
    *   <li>IP -> CHARACTER
+   *   <li>NUMBER -> VARCHAR
    * </ul>
    */
   private static final Map<SqlTypeName, ImmutableSet<@NonNull SqlTypeName>> additionalMapping =
       Map.of(
           SqlTypeName.OTHER,
           ImmutableSet.of(SqlTypeName.OTHER, SqlTypeName.VARCHAR, SqlTypeName.CHAR),
           SqlTypeName.VARCHAR,
-          ImmutableSet.of(SqlTypeName.OTHER),
+          ImmutableSet.<SqlTypeName>builder()
+              .add(SqlTypeName.OTHER)
+              .addAll(SqlTypeName.NUMERIC_TYPES)
+              .build(),
           SqlTypeName.CHAR,
           ImmutableSet.of(SqlTypeName.OTHER));
 

core/src/main/java/org/opensearch/sql/expression/function/PPLBuiltinOperators.java

@@ -80,7 +80,6 @@
 import org.opensearch.sql.expression.function.udf.ToNumberFunction;
 import org.opensearch.sql.expression.function.udf.ToStringFunction;
 import org.opensearch.sql.expression.function.udf.condition.EarliestFunction;
-import org.opensearch.sql.expression.function.udf.condition.EnhancedCoalesceFunction;
 import org.opensearch.sql.expression.function.udf.condition.LatestFunction;
 import org.opensearch.sql.expression.function.udf.datetime.AddSubDateFunction;
 import org.opensearch.sql.expression.function.udf.datetime.CurrentFunction;
@@ -488,9 +487,6 @@ public class PPLBuiltinOperators extends ReflectiveSqlOperatorTable {
           PPLReturnTypes.STRING_ARRAY,
           PPLOperandTypes.ANY_SCALAR_OPTIONAL_INTEGER);
 
-  public static final SqlFunction ENHANCED_COALESCE =
-      new EnhancedCoalesceFunction().toUDF("COALESCE");
-
   public static final SqlFunction ATAN =
       new SqlFunction(
           "ATAN",

core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java

@@ -829,7 +829,7 @@ void populate() {
       registerOperator(IFNULL, SqlStdOperatorTable.COALESCE);
       registerOperator(EARLIEST, PPLBuiltinOperators.EARLIEST);
       registerOperator(LATEST, PPLBuiltinOperators.LATEST);
-      registerOperator(COALESCE, PPLBuiltinOperators.ENHANCED_COALESCE);
+      registerOperator(COALESCE, SqlStdOperatorTable.COALESCE);
 
       // Register library operator
       registerOperator(REGEXP, PPLBuiltinOperators.REGEXP);