Support function coalesce with Calcite

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

Author: yuancu

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

@@ -226,6 +226,7 @@ public enum BuiltinFunctionName {
   IF(FunctionName.of("if")),
   NULLIF(FunctionName.of("nullif")),
   ISNULL(FunctionName.of("isnull")),
+  COALESCE(FunctionName.of("coalesce")),
 
   ROW_NUMBER(FunctionName.of("row_number")),
   RANK(FunctionName.of("rank")),

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

@@ -202,6 +202,7 @@ void populate() {
       registerOperator(IS_NULL, SqlStdOperatorTable.IS_NULL);
       registerOperator(IF, SqlStdOperatorTable.CASE);
       registerOperator(IFNULL, SqlStdOperatorTable.COALESCE);
+      registerOperator(COALESCE, SqlStdOperatorTable.COALESCE);
 
       // Register library operator
       registerOperator(REGEXP, SqlLibraryOperators.REGEXP);

docs/user/ppl/functions/condition.rst

@@ -238,3 +238,29 @@ Example::
     | Dale      | Adams    | 33  |
     +-----------+----------+-----+
 
+COALESCE
+--------
+
+Description
+>>>>>>>>>>>
+
+Version: 3.1.0
+
+Usage: coalesce(field1, field2, ...) return the first non-null value in the argument list.
+
+Argument type: all the supported data type, (NOTE : if parameters have different type, you will fail semantic check)
+
+Return type: any
+
+Example::
+
+    os> source=accounts | eval result = coalesce(employer, firstname, lastname) | fields result, firstname, lastname, employer
+    fetched rows / total rows = 4/4
+    +---------+-----------+----------+----------+
+    | result  | firstname | lastname | employer |
+    |---------+-----------+----------+----------|
+    | Pyrami  | Amber     | Duke     | Pyrami   |
+    | Netagy  | Hattie    | Bond     | Netagy   |
+    | Quility | Nanette   | Bates    | Quility  |
+    | Dale    | Dale      | Adams    | null     |
+    +---------+-----------+----------+----------+

integ-test/src/test/java/org/opensearch/sql/calcite/standalone/CalcitePPLConditionBuiltinFunctionIT.java

@@ -108,6 +108,21 @@ public void testIfNull() {
         rows("Hello", 30));
   }
 
+  @Test
+  public void testCoalesce() {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                "source=%s | where age = 10 | eval new_country = coalesce(name, state, country) | fields name, state, country, new_country",
+                TEST_INDEX_STATE_COUNTRY_WITH_NULL));
+
+    verifySchema(actual, schema("name", "string"), schema("state", "string"), schema("country", "string"), schema("new_country", "string"));
+
+    verifyDataRows(
+        actual,
+        rows(null, null, "Canada", "Canada"));
+  }
+
   @Test
   public void testIf() {
     JSONObject actual =

ppl/src/main/antlr/OpenSearchPPLLexer.g4

@@ -376,6 +376,7 @@ IFNULL:                             'IFNULL';
 NULLIF:                             'NULLIF';
 IF:                                 'IF';
 TYPEOF:                             'TYPEOF';
+COALESCE:                           'COALESCE';
 
 // RELEVANCE FUNCTIONS AND PARAMETERS
 MATCH:                              'MATCH';

ppl/src/main/antlr/OpenSearchPPLParser.g4

@@ -841,6 +841,7 @@ flowControlFunctionName
    : IF
    | IFNULL
    | NULLIF
+   | COALESCE
    ;
 
 systemFunctionName