[DAPHNE-#494] SQLParser: GROUP BY without aggregation clause (#543)

- Add simple test which checks if the SQL grouping works without an aggregation function.
- Implement a workaround to allow the use of the group operation without aggregations.
- Fixed shape inference for GroupOp.
- Hardcode the addition to the callee in the kernel lowering as a workaround for grouping without aggregation.
- Closes #494.

src/compiler/lowering/RewriteToCallKernelOpPass.cpp

@@ -92,7 +92,7 @@ namespace
             }
             if(auto concreteOp = llvm::dyn_cast<daphne::GroupOp>(op)) {
                 auto idxAndLen = concreteOp.getODSOperandIndexAndLength(index);
-                static bool isVariadic[] = {false, true, true, true};
+                static bool isVariadic[] = {false, true, true};
                 return std::make_tuple(
                         idxAndLen.first,
                         idxAndLen.second,
@@ -214,8 +214,18 @@ namespace
                     const unsigned idx = std::get<0>(odsOpInfo);
                     const unsigned len = std::get<1>(odsOpInfo);
                     const bool isVariadic = std::get<2>(odsOpInfo);
+
+                    // TODO The group operation currently expects at least four inputs due to the
+                    // expectation of a aggregation. To make the group operation possible without aggregations,
+                    // we have to use this workaround to create the correct name and skip the creation
+                    // of the variadic pack ops. Should be changed when reworking the lowering to kernels.
+                    if(llvm::dyn_cast<daphne::GroupOp>(op) && idx >= operandTypes.size()) {
+                        callee << "__char_variadic__size_t";
+                        continue;
+                    } else {
+                        callee << "__" << CompilerUtils::mlirTypeToCppTypeName(operandTypes[idx], generalizeInputTypes);
+                    }
 
-                    callee << "__" << CompilerUtils::mlirTypeToCppTypeName(operandTypes[idx], generalizeInputTypes);
                     if(isVariadic) {
                         // Variadic operand.
                         callee << "_variadic__size_t";

src/ir/daphneir/DaphneInferShapeOpInterface.cpp

@@ -184,7 +184,7 @@ std::vector<std::pair<ssize_t, ssize_t>> daphne::GroupJoinOp::inferShape() {
 std::vector<std::pair<ssize_t, ssize_t>> daphne::GroupOp::inferShape() {
     // We don't know the exact number of groups here.
     const size_t numRows = -1;
-    const size_t numCols = inferNumColsFromArgs(getKeyCol()) + inferNumColsFromArgs(getAggCol());
+    const size_t numCols = getKeyCol().size() + getAggCol().size();
     return {{numRows, numCols}};
 }
 

test/api/cli/sql/SQLResultTest.cpp

@@ -34,4 +34,4 @@ const std::string dirPath = "test/api/cli/sql/";
         } \
     }
 
-MAKE_TEST_CASE("group", 1)
+MAKE_TEST_CASE("group", 2)

test/api/cli/sql/group_2.daphne

@@ -0,0 +1,6 @@
+# GROUP BY without aggregation.
+
+f = createFrame([0, 1, 1, 3, 1, 5, 1, 3, 0, 9], "a");
+registerView("f", f);
+res = sql("SELECT f.a FROM f GROUP BY f.a;");
+print(res);

test/api/cli/sql/group_2.txt

@@ -0,0 +1,6 @@
+Frame(5x1, [f.a:int64_t])
+0
+1
+3
+5
+9