Change args in case function (#2763)

pkg/sql/plan2/build_expr.go

@@ -229,62 +229,57 @@ func buildCastExpr(astExpr *tree.CastExpr, ctx CompilerContext, query *Query, no
 
 func buildCaseExpr(astExpr *tree.CaseExpr, ctx CompilerContext, query *Query, node *Node, binderCtx *BinderContext, needAgg bool) (expr *Expr, isAgg bool, err error) {
 	var args []*Expr
+	var caseExpr *Expr
 
 	if astExpr.Expr != nil {
-		caseExpr, _, err := buildExpr(astExpr.Expr, ctx, query, node, binderCtx, needAgg)
+		caseExpr, _, err = buildExpr(astExpr.Expr, ctx, query, node, binderCtx, needAgg)
 		if err != nil {
 			return nil, false, err
 		}
-		args = append(args, caseExpr)
 	}
 
 	isAgg = true
-	whenList := make([]*Expr, len(astExpr.Whens))
-	for idx, whenExpr := range astExpr.Whens {
-		exprs := make([]*Expr, 2)
-		expr, paramIsAgg, err := buildExpr(whenExpr.Cond, ctx, query, node, binderCtx, needAgg)
+	for _, whenExpr := range astExpr.Whens {
+		condExpr, paramIsAgg, err := buildExpr(whenExpr.Cond, ctx, query, node, binderCtx, needAgg)
 		if err != nil {
 			return nil, false, err
 		}
 		isAgg = isAgg && paramIsAgg
-		exprs[0] = expr
-		expr, paramIsAgg, err = buildExpr(whenExpr.Val, ctx, query, node, binderCtx, needAgg)
+		if caseExpr != nil {
+			// rewrite "case col when 1 then '1' else '2'" to "case when col=1 then '1' else '2'"
+			condExpr, _, err = getFunctionExprByNameAndPlanExprs("=", []*Expr{caseExpr, condExpr})
+			if err != nil {
+				return nil, false, err
+			}
+		}
+		args = append(args, condExpr)
+
+		valExpr, paramIsAgg, err := buildExpr(whenExpr.Val, ctx, query, node, binderCtx, needAgg)
 		if err != nil {
 			return nil, false, err
 		}
 		isAgg = isAgg && paramIsAgg
-		exprs[1] = expr
-
-		whenList[idx] = &Expr{
-			Expr: &plan.Expr_List{
-				List: &plan.ExprList{
-					List: exprs,
-				},
-			},
-			Typ: &plan.Type{
-				Id: plan.Type_TUPLE,
-			},
-		}
-	}
-	whenExpr := &Expr{
-		Expr: &plan.Expr_List{
-			List: &plan.ExprList{
-				List: whenList,
-			},
-		},
-		Typ: &plan.Type{
-			Id: plan.Type_TUPLE,
-		},
+		args = append(args, valExpr)
 	}
-	args = append(args, whenExpr)
 
 	if astExpr.Else != nil {
-		elseExpr, paramIsAgg, err := buildExpr(astExpr.Else, ctx, query, node, binderCtx, needAgg)
+		elseExpr, _, err := buildExpr(astExpr.Else, ctx, query, node, binderCtx, needAgg)
 		if err != nil {
 			return nil, false, err
 		}
-		isAgg = isAgg && paramIsAgg
 		args = append(args, elseExpr)
+	} else {
+		args = append(args, &Expr{
+			Expr: &plan.Expr_C{
+				C: &Const{
+					Isnull: true,
+				},
+			},
+			Typ: &plan.Type{
+				Id:       plan.Type_ANY,
+				Nullable: true,
+			},
+		})
 	}
 	return getFunctionExprByNameAndPlanExprs("case", args)
 }