Join side aliases should be optional

docs/ppl-lang/PPL-Example-Commands.md

@@ -298,7 +298,11 @@ source = table |  where ispresent(a) |
 - `source = table1 | left semi join left = l right = r on l.a = r.a table2`
 - `source = table1 | left anti join left = l right = r on l.a = r.a table2`
 - `source = table1 | join left = l right = r [ source = table2 | where d > 10 | head 5 ]`
-
+- `source = table1 | inner join on table1.a = table2.a table2 | fields table1.a, table2.a, table1.b, table1.c` (directly refer table name)
+- `source = table1 | inner join on a = c table2 | fields a, b, c, d` (ignore side aliases as long as no ambiguous)
+- `source = table1 as t1 | join left = l right = r on l.a = r.a table2 as t2 | fields l.a, r.a` (side alias overrides table alias)
+- `source = table1 as t1 | join left = l right = r on l.a = r.a table2 as t2 | fields t1.a, t2.a` (error, side alias overrides table alias)
+- `source = table1 | join left = l right = r on l.a = r.a [ source = table2 ] as s | fields l.a, s.a` (error, side alias overrides subquery alias)
 
 #### **Lookup**
 [See additional command details](ppl-lookup-command.md)

docs/ppl-lang/ppl-join-command.md

@@ -65,8 +65,8 @@ WHERE t1.serviceName = `order`
 SEARCH source=<left-table>
 | <other piped command>
 | [joinType] JOIN
-    leftAlias
-    rightAlias
+    [leftAlias]
+    [rightAlias]
     [joinHints]
     ON joinCriteria
     <right-table>
@@ -79,12 +79,12 @@ SEARCH source=<left-table>
 
 **leftAlias**
 - Syntax: `left = <leftAlias>`
-- Required
+- Optional
 - Description: The subquery alias to use with the left join side, to avoid ambiguous naming.
 
 **rightAlias**
 - Syntax: `right = <rightAlias>`
-- Required
+- Optional
 - Description: The subquery alias to use with the right join side, to avoid ambiguous naming.
 
 **joinHints**
@@ -138,11 +138,11 @@ Rewritten by PPL Join query:
 ```sql
 SEARCH source=customer
 | FIELDS c_custkey
-| LEFT OUTER JOIN left = c, right = o
-    ON c.c_custkey = o.o_custkey AND o_comment NOT LIKE '%unusual%packages%'
+| LEFT OUTER JOIN
+    ON c_custkey = o_custkey AND o_comment NOT LIKE '%unusual%packages%'
     orders
-| STATS count(o_orderkey) AS c_count BY c.c_custkey
-| STATS count(1) AS custdist BY c_count
+| STATS count(o_orderkey) AS c_count BY c_custkey
+| STATS count() AS custdist BY c_count
 | SORT - custdist, - c_count
 ```
 _- **Limitation: sub-searches is unsupported in join right side**_
@@ -151,14 +151,15 @@ If sub-searches is supported, above ppl query could be rewritten as:
 ```sql
 SEARCH source=customer
 | FIELDS c_custkey
-| LEFT OUTER JOIN left = c, right = o ON c.c_custkey = o.o_custkey
+| LEFT OUTER JOIN
+   ON c_custkey = o_custkey
    [
       SEARCH source=orders
       | WHERE o_comment NOT LIKE '%unusual%packages%'
       | FIELDS o_orderkey, o_custkey
    ]
-| STATS count(o_orderkey) AS c_count BY c.c_custkey
-| STATS count(1) AS custdist BY c_count
+| STATS count(o_orderkey) AS c_count BY c_custkey
+| STATS count() AS custdist BY c_count
 | SORT - custdist, - c_count
 ```
 

integ-test/src/integration/scala/org/opensearch/flint/spark/ppl/FlintSparkPPLBasicITSuite.scala

@@ -597,4 +597,68 @@ class FlintSparkPPLBasicITSuite
           | """.stripMargin))
     assert(ex.getMessage().contains("Invalid table name"))
   }
+
+  test("Search multiple tables - translated into union call with fields") {
+    val frame = sql(s"""
+                       | source = $t1, $t2
+                       | """.stripMargin)
+    assertSameRows(
+      Seq(
+        Row("Hello", 30, "New York", "USA", 2023, 4),
+        Row("Hello", 30, "New York", "USA", 2023, 4),
+        Row("Jake", 70, "California", "USA", 2023, 4),
+        Row("Jake", 70, "California", "USA", 2023, 4),
+        Row("Jane", 20, "Quebec", "Canada", 2023, 4),
+        Row("Jane", 20, "Quebec", "Canada", 2023, 4),
+        Row("John", 25, "Ontario", "Canada", 2023, 4),
+        Row("John", 25, "Ontario", "Canada", 2023, 4)),
+      frame)
+
+    val logicalPlan: LogicalPlan = frame.queryExecution.logical
+    val table1 = UnresolvedRelation(Seq("spark_catalog", "default", "flint_ppl_test1"))
+    val table2 = UnresolvedRelation(Seq("spark_catalog", "default", "flint_ppl_test2"))
+
+    val allFields1 = UnresolvedStar(None)
+    val allFields2 = UnresolvedStar(None)
+
+    val projectedTable1 = Project(Seq(allFields1), table1)
+    val projectedTable2 = Project(Seq(allFields2), table2)
+
+    val expectedPlan =
+      Union(Seq(projectedTable1, projectedTable2), byName = true, allowMissingCol = true)
+
+    comparePlans(expectedPlan, logicalPlan, checkAnalysis = false)
+  }
+
+  test("Search multiple tables - with table alias") {
+    val frame = sql(s"""
+                       | source = $t1, $t2 as t | where t.country = "USA"
+                       | """.stripMargin)
+    assertSameRows(
+      Seq(
+        Row("Hello", 30, "New York", "USA", 2023, 4),
+        Row("Hello", 30, "New York", "USA", 2023, 4),
+        Row("Jake", 70, "California", "USA", 2023, 4),
+        Row("Jake", 70, "California", "USA", 2023, 4)),
+      frame)
+
+    val logicalPlan: LogicalPlan = frame.queryExecution.logical
+    val table1 = UnresolvedRelation(Seq("spark_catalog", "default", "flint_ppl_test1"))
+    val table2 = UnresolvedRelation(Seq("spark_catalog", "default", "flint_ppl_test2"))
+
+    val plan1 = Filter(
+      EqualTo(UnresolvedAttribute("t.country"), Literal("USA")),
+      SubqueryAlias("t", table1))
+    val plan2 = Filter(
+      EqualTo(UnresolvedAttribute("t.country"), Literal("USA")),
+      SubqueryAlias("t", table2))
+
+    val projectedTable1 = Project(Seq(UnresolvedStar(None)), plan1)
+    val projectedTable2 = Project(Seq(UnresolvedStar(None)), plan2)
+
+    val expectedPlan =
+      Union(Seq(projectedTable1, projectedTable2), byName = true, allowMissingCol = true)
+
+    comparePlans(expectedPlan, logicalPlan, checkAnalysis = false)
+  }
 }