Add OUTPUT as an alias for REPLACE in Lookup

docs/user/ppl/cmd/lookup.md

@@ -8,7 +8,7 @@ The `lookup` command enriches search data by adding or replacing values from a l
 The `lookup` command has the following syntax:
 
 ```syntax
-lookup <lookupIndex> (<lookupMappingField> [as <sourceMappingField>])... [(replace | append) (<inputField> [as <outputField>])...]
+lookup <lookupIndex> (<lookupMappingField> [as <sourceMappingField>])... [(replace | append | output) (<inputField> [as <outputField>])...]
 ```
 
 The following are examples of the `lookup` command syntax:
@@ -21,6 +21,8 @@ source = table1 | lookup table2 id as cid, name replace dept as department
 source = table1 | lookup table2 id as cid, name replace dept as department, city as location
 source = table1 | lookup table2 id as cid, name append dept as department
 source = table1 | lookup table2 id as cid, name append dept as department, city as location
+source = table1 | lookup table2 id as cid, name output dept as department
+source = table1 | lookup table2 id as cid, name output dept as department, city as location
 ```
 
 ## Parameters
@@ -34,7 +36,7 @@ The `lookup` command supports the following parameters.
 | `<sourceMappingField>` | Optional | A key from the source data (left side) used for matching, similar to a join key in the left table. Default is `lookupMappingField`. |
 | `<inputField>` | Optional | A field in the lookup index whose matched values are applied to the results (output). Specify multiple fields as a comma-separated list. If not specified, all fields except `lookupMappingField` from the lookup index are applied to the results. |
 | `<outputField>` | Optional | The name of the field in the results (output) in which matched values are placed. Specify multiple fields as a comma-separated list. If the `outputField` specifies an existing field in the source query, its values are replaced or appended with matched values from the `inputField`. If the field specified in the `outputField` is not an existing field, a new field is added to the results when using `replace`, or the operation fails when using `append`. |
-| `(replace | append)` | Optional | Specifies how matched values are applied to the output. `replace` overwrites existing values with matched values from the lookup index. `append` fills only missing values in the results with matched values from the lookup index. Default is `replace`. |
+| `(replace \| append \| output)` | Optional | Specifies how matched values are applied to the output. `replace` overwrites existing values with matched values from the lookup index. `append` fills only missing values in the results with matched values from the lookup index. `output` is a synonym for `replace` (provided for SPL compatibility). Default is `replace`. |
 
 ## Example 1: Replace existing values  
 
@@ -121,4 +123,29 @@ The query returns the following results:
 | 1005 | Jane  | Scientist  | Canada  | 90000  | Engineer  |
 | 1002 | John  | Doctor     | Canada  | 120000 | Scientist |
 +------+-------+------------+---------+--------+-----------+
-```
+```
+
+## Example 5: Using OUTPUT keyword
+
+The `OUTPUT` keyword is a synonym for `REPLACE`. The following query demonstrates using `OUTPUT` to overwrite existing values:
+
+```ppl ignore
+source = worker
+  | LOOKUP work_information uid AS id OUTPUT department
+  | fields id, name, occupation, country, salary, department
+```
+
+This query produces the same results as Example 1 (using `REPLACE`):
+
+```text
++------+-------+------------+---------+--------+------------+
+| id   | name  | occupation | country | salary | department |
+|------+-------+------------+---------+--------+------------|
+| 1000 | Jake  | Engineer   | England | 100000 | IT         |
+| 1001 | Hello | Artist     | USA     | 70000  | null       |
+| 1002 | John  | Doctor     | Canada  | 120000 | DATA       |
+| 1003 | David | Doctor     | null    | 120000 | HR         |
+| 1004 | David | null       | Canada  | 0      | null       |
+| 1005 | Jane  | Scientist  | Canada  | 90000  | DATA       |
++------+-------+------------+---------+--------+------------+
+```

integ-test/src/test/java/org/opensearch/sql/calcite/remote/CalcitePPLLookupIT.java

@@ -438,4 +438,59 @@ public void testRnameAsIdShouldnWork() throws IOException {
                 TEST_INDEX_WORKER, TEST_INDEX_WORK_INFORMATION));
     verifyNumOfRows(result, 6);
   }
+
+  @Test
+  public void testUidAsIdOutputDepartment() throws IOException {
+    // OUTPUT is a synonym for REPLACE (SPL compatibility)
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source = %s"
+                    + "| LOOKUP %s uid AS id OUTPUT department"
+                    + "| fields id, name, occupation, country, salary, department",
+                TEST_INDEX_WORKER, TEST_INDEX_WORK_INFORMATION));
+    verifySchema(
+        result,
+        schema("id", "int"),
+        schema("name", "string"),
+        schema("occupation", "string"),
+        schema("country", "string"),
+        schema("salary", "int"),
+        schema("department", "string"));
+    verifyDataRows(
+        result,
+        rows(1000, "Jake", "Engineer", "England", 100000, "IT"),
+        rows(1001, "Hello", "Artist", "USA", 70000, null),
+        rows(1002, "John", "Doctor", "Canada", 120000, "DATA"),
+        rows(1003, "David", "Doctor", null, 120000, "HR"),
+        rows(1004, "David", null, "Canada", 0, null),
+        rows(1005, "Jane", "Scientist", "Canada", 90000, "DATA"));
+  }
+
+  @Test
+  public void testUidAsIdOutputDepartmentAsCountry() throws IOException {
+    // OUTPUT with field aliasing (SPL compatibility)
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source = %s"
+                    + "| LOOKUP %s uid AS id OUTPUT department AS country"
+                    + "| fields id, name, occupation, salary, country",
+                TEST_INDEX_WORKER, TEST_INDEX_WORK_INFORMATION));
+    verifySchema(
+        result,
+        schema("id", "int"),
+        schema("name", "string"),
+        schema("occupation", "string"),
+        schema("salary", "int"),
+        schema("country", "string"));
+    verifyDataRows(
+        result,
+        rows(1000, "Jake", "Engineer", 100000, "IT"),
+        rows(1001, "Hello", "Artist", 70000, null),
+        rows(1002, "John", "Doctor", 120000, "DATA"),
+        rows(1003, "David", "Doctor", 120000, "HR"),
+        rows(1004, "David", null, 0, null),
+        rows(1005, "Jane", "Scientist", 90000, "DATA"));
+  }
 }

ppl/src/main/antlr/OpenSearchPPLParser.g4

@@ -476,7 +476,7 @@ patternMode
 
 // lookup
 lookupCommand
-   : LOOKUP tableSource lookupMappingList ((APPEND | REPLACE) outputCandidateList)?
+   : LOOKUP tableSource lookupMappingList ((APPEND | REPLACE | OUTPUT) outputCandidateList)?
    ;
 
 lookupMappingList

ppl/src/main/java/org/opensearch/sql/ppl/parser/AstBuilder.java

@@ -972,6 +972,7 @@ public UnresolvedPlan visitPatternsCommand(OpenSearchPPLParser.PatternsCommandCo
   @Override
   public UnresolvedPlan visitLookupCommand(OpenSearchPPLParser.LookupCommandContext ctx) {
     Relation lookupRelation = new Relation(this.internalVisitExpression(ctx.tableSource()));
+    // OUTPUT and REPLACE are synonyms - both overwrite existing fields
     Lookup.OutputStrategy strategy =
         ctx.APPEND() != null ? Lookup.OutputStrategy.APPEND : Lookup.OutputStrategy.REPLACE;
     java.util.Map<String, String> mappingAliasMap =

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

@@ -122,6 +122,114 @@ public void testReplaceAs() {
     verifyPPLToSparkSQL(root, expectedSparkSql);
   }
 
+  @Test
+  public void testOutput() {
+    // OUTPUT is a synonym for REPLACE (for SPL compatibility)
+    String ppl = "source=EMP | lookup DEPT DEPTNO output LOC";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalProject(EMPNO=[$0], ENAME=[$1], JOB=[$2], MGR=[$3], HIREDATE=[$4], SAL=[$5],"
+            + " COMM=[$6], DEPTNO=[$7], LOC=[$8])\n"
+            + "  LogicalJoin(condition=[=($7, $9)], joinType=[left])\n"
+            + "    LogicalTableScan(table=[[scott, EMP]])\n"
+            + "    LogicalProject(LOC=[$2], DEPTNO=[$0])\n"
+            + "      LogicalTableScan(table=[[scott, DEPT]])\n";
+    verifyLogical(root, expectedLogical);
+
+    String expectedResult =
+        "EMPNO=7782; ENAME=CLARK; JOB=MANAGER; MGR=7839; HIREDATE=1981-06-09; SAL=2450.00;"
+            + " COMM=null; DEPTNO=10; LOC=NEW YORK\n"
+            + "EMPNO=7839; ENAME=KING; JOB=PRESIDENT; MGR=null; HIREDATE=1981-11-17; SAL=5000.00;"
+            + " COMM=null; DEPTNO=10; LOC=NEW YORK\n"
+            + "EMPNO=7934; ENAME=MILLER; JOB=CLERK; MGR=7782; HIREDATE=1982-01-23; SAL=1300.00;"
+            + " COMM=null; DEPTNO=10; LOC=NEW YORK\n"
+            + "EMPNO=7369; ENAME=SMITH; JOB=CLERK; MGR=7902; HIREDATE=1980-12-17; SAL=800.00;"
+            + " COMM=null; DEPTNO=20; LOC=DALLAS\n"
+            + "EMPNO=7566; ENAME=JONES; JOB=MANAGER; MGR=7839; HIREDATE=1981-02-04; SAL=2975.00;"
+            + " COMM=null; DEPTNO=20; LOC=DALLAS\n"
+            + "EMPNO=7788; ENAME=SCOTT; JOB=ANALYST; MGR=7566; HIREDATE=1987-04-19; SAL=3000.00;"
+            + " COMM=null; DEPTNO=20; LOC=DALLAS\n"
+            + "EMPNO=7876; ENAME=ADAMS; JOB=CLERK; MGR=7788; HIREDATE=1987-05-23; SAL=1100.00;"
+            + " COMM=null; DEPTNO=20; LOC=DALLAS\n"
+            + "EMPNO=7902; ENAME=FORD; JOB=ANALYST; MGR=7566; HIREDATE=1981-12-03; SAL=3000.00;"
+            + " COMM=null; DEPTNO=20; LOC=DALLAS\n"
+            + "EMPNO=7499; ENAME=ALLEN; JOB=SALESMAN; MGR=7698; HIREDATE=1981-02-20; SAL=1600.00;"
+            + " COMM=300.00; DEPTNO=30; LOC=CHICAGO\n"
+            + "EMPNO=7521; ENAME=WARD; JOB=SALESMAN; MGR=7698; HIREDATE=1981-02-22; SAL=1250.00;"
+            + " COMM=500.00; DEPTNO=30; LOC=CHICAGO\n"
+            + "EMPNO=7654; ENAME=MARTIN; JOB=SALESMAN; MGR=7698; HIREDATE=1981-09-28; SAL=1250.00;"
+            + " COMM=1400.00; DEPTNO=30; LOC=CHICAGO\n"
+            + "EMPNO=7698; ENAME=BLAKE; JOB=MANAGER; MGR=7839; HIREDATE=1981-01-05; SAL=2850.00;"
+            + " COMM=null; DEPTNO=30; LOC=CHICAGO\n"
+            + "EMPNO=7844; ENAME=TURNER; JOB=SALESMAN; MGR=7698; HIREDATE=1981-09-08; SAL=1500.00;"
+            + " COMM=0.00; DEPTNO=30; LOC=CHICAGO\n"
+            + "EMPNO=7900; ENAME=JAMES; JOB=CLERK; MGR=7698; HIREDATE=1981-12-03; SAL=950.00;"
+            + " COMM=null; DEPTNO=30; LOC=CHICAGO\n";
+    verifyResult(root, expectedResult);
+
+    String expectedSparkSql =
+        "SELECT `EMP`.`EMPNO`, `EMP`.`ENAME`, `EMP`.`JOB`, `EMP`.`MGR`, `EMP`.`HIREDATE`,"
+            + " `EMP`.`SAL`, `EMP`.`COMM`, `EMP`.`DEPTNO`, `t`.`LOC`\n"
+            + "FROM `scott`.`EMP`\n"
+            + "LEFT JOIN (SELECT `LOC`, `DEPTNO`\n"
+            + "FROM `scott`.`DEPT`) `t` ON `EMP`.`DEPTNO` = `t`.`DEPTNO`";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
+  @Test
+  public void testOutputAs() {
+    // OUTPUT with field aliasing (SPL compatibility)
+    String ppl = "source=EMP | lookup DEPT DEPTNO output LOC as JOB";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalProject(EMPNO=[$0], ENAME=[$1], MGR=[$3], HIREDATE=[$4], SAL=[$5], COMM=[$6],"
+            + " DEPTNO=[$7], JOB=[$8])\n"
+            + "  LogicalJoin(condition=[=($7, $9)], joinType=[left])\n"
+            + "    LogicalTableScan(table=[[scott, EMP]])\n"
+            + "    LogicalProject(LOC=[$2], DEPTNO=[$0])\n"
+            + "      LogicalTableScan(table=[[scott, DEPT]])\n";
+    verifyLogical(root, expectedLogical);
+
+    String expectedResult =
+        "EMPNO=7782; ENAME=CLARK; MGR=7839; HIREDATE=1981-06-09; SAL=2450.00; COMM=null; DEPTNO=10;"
+            + " JOB=NEW YORK\n"
+            + "EMPNO=7839; ENAME=KING; MGR=null; HIREDATE=1981-11-17; SAL=5000.00; COMM=null;"
+            + " DEPTNO=10; JOB=NEW YORK\n"
+            + "EMPNO=7934; ENAME=MILLER; MGR=7782; HIREDATE=1982-01-23; SAL=1300.00; COMM=null;"
+            + " DEPTNO=10; JOB=NEW YORK\n"
+            + "EMPNO=7369; ENAME=SMITH; MGR=7902; HIREDATE=1980-12-17; SAL=800.00; COMM=null;"
+            + " DEPTNO=20; JOB=DALLAS\n"
+            + "EMPNO=7566; ENAME=JONES; MGR=7839; HIREDATE=1981-02-04; SAL=2975.00; COMM=null;"
+            + " DEPTNO=20; JOB=DALLAS\n"
+            + "EMPNO=7788; ENAME=SCOTT; MGR=7566; HIREDATE=1987-04-19; SAL=3000.00; COMM=null;"
+            + " DEPTNO=20; JOB=DALLAS\n"
+            + "EMPNO=7876; ENAME=ADAMS; MGR=7788; HIREDATE=1987-05-23; SAL=1100.00; COMM=null;"
+            + " DEPTNO=20; JOB=DALLAS\n"
+            + "EMPNO=7902; ENAME=FORD; MGR=7566; HIREDATE=1981-12-03; SAL=3000.00; COMM=null;"
+            + " DEPTNO=20; JOB=DALLAS\n"
+            + "EMPNO=7499; ENAME=ALLEN; MGR=7698; HIREDATE=1981-02-20; SAL=1600.00; COMM=300.00;"
+            + " DEPTNO=30; JOB=CHICAGO\n"
+            + "EMPNO=7521; ENAME=WARD; MGR=7698; HIREDATE=1981-02-22; SAL=1250.00; COMM=500.00;"
+            + " DEPTNO=30; JOB=CHICAGO\n"
+            + "EMPNO=7654; ENAME=MARTIN; MGR=7698; HIREDATE=1981-09-28; SAL=1250.00; COMM=1400.00;"
+            + " DEPTNO=30; JOB=CHICAGO\n"
+            + "EMPNO=7698; ENAME=BLAKE; MGR=7839; HIREDATE=1981-01-05; SAL=2850.00; COMM=null;"
+            + " DEPTNO=30; JOB=CHICAGO\n"
+            + "EMPNO=7844; ENAME=TURNER; MGR=7698; HIREDATE=1981-09-08; SAL=1500.00; COMM=0.00;"
+            + " DEPTNO=30; JOB=CHICAGO\n"
+            + "EMPNO=7900; ENAME=JAMES; MGR=7698; HIREDATE=1981-12-03; SAL=950.00; COMM=null;"
+            + " DEPTNO=30; JOB=CHICAGO\n";
+    verifyResult(root, expectedResult);
+
+    String expectedSparkSql =
+        "SELECT `EMP`.`EMPNO`, `EMP`.`ENAME`, `EMP`.`MGR`, `EMP`.`HIREDATE`, `EMP`.`SAL`,"
+            + " `EMP`.`COMM`, `EMP`.`DEPTNO`, `t`.`LOC` `JOB`\n"
+            + "FROM `scott`.`EMP`\n"
+            + "LEFT JOIN (SELECT `LOC`, `DEPTNO`\n"
+            + "FROM `scott`.`DEPT`) `t` ON `EMP`.`DEPTNO` = `t`.`DEPTNO`";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
   @Ignore
   public void testMultipleLookupKeysReplace() {
     String ppl =