A constant can be used outside aggregation only queries (elastic#34576)

A constant can now be used outside aggregation only queries.
Don't skip an ES query in case of constants-only selects.
Loosen the binary pipe restriction of being used only in aggregation queries.
Fixes elastic#31863

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/expression/gen/pipeline/BinaryPipe.java

@@ -41,7 +41,7 @@ public Pipe right() {
 
     @Override
     public boolean supportedByAggsOnlyQuery() {
-        return left.supportedByAggsOnlyQuery() && right.supportedByAggsOnlyQuery();
+        return left.supportedByAggsOnlyQuery() || right.supportedByAggsOnlyQuery();
     }
 
     @Override

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/expression/gen/pipeline/ConstantInput.java

@@ -30,7 +30,7 @@ public Processor asProcessor() {
 
     @Override
     public final boolean supportedByAggsOnlyQuery() {
-        return true;
+        return false;
     }
 
     @Override

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/optimizer/Optimizer.java

@@ -51,6 +51,7 @@
 import org.elasticsearch.xpack.sql.expression.predicate.operator.comparison.LessThan;
 import org.elasticsearch.xpack.sql.expression.predicate.operator.comparison.LessThanOrEqual;
 import org.elasticsearch.xpack.sql.plan.logical.Aggregate;
+import org.elasticsearch.xpack.sql.plan.logical.EsRelation;
 import org.elasticsearch.xpack.sql.plan.logical.Filter;
 import org.elasticsearch.xpack.sql.plan.logical.Limit;
 import org.elasticsearch.xpack.sql.plan.logical.LocalRelation;
@@ -1796,7 +1797,7 @@ protected LogicalPlan rule(LogicalPlan plan) {
             if (plan instanceof Project) {
                 Project p = (Project) plan;
                 List<Object> values = extractConstants(p.projections());
-                if (values.size() == p.projections().size()) {
+                if (values.size() == p.projections().size() && !(p.child() instanceof EsRelation)) {
                     return new LocalRelation(p.location(), new SingletonExecutable(p.output(), values.toArray()));
                 }
             }

x-pack/plugin/sql/src/test/java/org/elasticsearch/xpack/sql/expression/gen/pipeline/BinaryPipesTests.java

@@ -24,8 +24,8 @@ public void testSupportedByAggsOnlyQuery() {
         Pipe unsupported = new DummyPipe(false);
 
         assertFalse(new DummyBinaryPipe(unsupported, unsupported).supportedByAggsOnlyQuery());
-        assertFalse(new DummyBinaryPipe(unsupported, supported).supportedByAggsOnlyQuery());
-        assertFalse(new DummyBinaryPipe(supported, unsupported).supportedByAggsOnlyQuery());
+        assertTrue(new DummyBinaryPipe(unsupported, supported).supportedByAggsOnlyQuery());
+        assertTrue(new DummyBinaryPipe(supported, unsupported).supportedByAggsOnlyQuery());
         assertTrue(new DummyBinaryPipe(supported, supported).supportedByAggsOnlyQuery());
     }
 

x-pack/qa/sql/src/main/resources/select.sql-spec

@@ -34,6 +34,24 @@ SELECT first_name, last_name FROM "test_emp" ORDER BY emp_no LIMIT 5;
 multipleColumnWithAliasWithAndWithoutAsWithLimit
 SELECT first_name f, last_name AS l FROM "test_emp" ORDER BY emp_no LIMIT 5;
 
+//
+// SELECT constant literals with FROM
+//
+
+constantWithLimit
+SELECT 3 FROM "test_emp" LIMIT 5;
+constantAndColumnWithLimit
+SELECT 3, first_name, last_name FROM "test_emp" ORDER BY emp_no LIMIT 5;
+constantComparisonWithLimit
+SELECT 1=1 AS bool FROM "test_emp" LIMIT 5;
+constantComparisonAndColumnWithLimit
+SELECT 1=1 AS bool, first_name, last_name FROM "test_emp" ORDER BY emp_no LIMIT 5;
+castWithLiteralWithFrom
+SELECT CAST(1 AS INT) AS constant FROM "test_emp" LIMIT 5;
+castWithLiteralAndColumnWithFrom
+SELECT CAST((CAST(languages AS BIT) OR CAST(1 AS BIT)) AS INT) AS bool FROM test_emp LIMIT 5;
+castWithColumnAndLiteralCombinedAndSelectColumnWithFrom
+SELECT CAST((CAST(languages AS BIT) OR CAST(1 AS BIT)) AS INT) AS bool, languages FROM test_emp ORDER BY languages LIMIT 5;
 
 //
 // SELECT with CAST