planner: add projections to keep join keys as col=col

pkg/planner/core/integration_test.go

@@ -2165,6 +2165,24 @@ func TestWindowRangeFramePushDownTiflash(t *testing.T) {
 		"          └─TableFullScan_9 10000.00 mpp[tiflash] table:first_range keep order:false, stats:pseudo"))
 }
 
+func TestIssue46556(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec(`use test`)
+	tk.MustExec(`CREATE TABLE t0(c0 BLOB);`)
+	tk.MustExec(`CREATE definer='root'@'localhost' VIEW v0(c0) AS SELECT NULL FROM t0 GROUP BY NULL;`)
+	tk.MustExec(`SELECT t0.c0 FROM t0 NATURAL JOIN v0 WHERE v0.c0 LIKE v0.c0;`) // no error
+	tk.MustQuery(`explain format='brief' SELECT t0.c0 FROM t0 NATURAL JOIN v0 WHERE v0.c0 LIKE v0.c0`).Check(
+		testkit.Rows(`HashJoin 0.00 root  inner join, equal:[eq(Column#9, Column#10)]`,
+			`├─Projection(Build) 0.00 root  cast(Column#5, double BINARY)->Column#9`,
+			`│ └─Projection 0.00 root  <nil>->Column#5`,
+			`│   └─TableDual 0.00 root  rows:0`,
+			`└─Projection(Probe) 9990.00 root  test.t0.c0, cast(test.t0.c0, double BINARY)->Column#10`,
+			`  └─TableReader 9990.00 root  data:Selection`,
+			`    └─Selection 9990.00 cop[tikv]  not(isnull(test.t0.c0))`,
+			`      └─TableFullScan 10000.00 cop[tikv] table:t0 keep order:false, stats:pseudo`))
+}
+
 // https://github.com/pingcap/tidb/issues/41458
 func TestIssue41458(t *testing.T) {
 	store := testkit.CreateMockStore(t)

pkg/planner/core/rule_join_reorder.go

@@ -514,13 +514,39 @@ func (s *baseSingleGroupJoinOrderSolver) checkConnection(leftPlan, rightPlan bas
 				usedEdges = append(usedEdges, edge)
 			} else {
 				newSf := expression.NewFunctionInternal(s.ctx.GetExprCtx(), ast.EQ, edge.GetType(), rCol, lCol).(*expression.ScalarFunction)
+
+				// after creating the new EQ function, the 2 args might not be column anymore, which breaks the assumption that
+				// join eq keys must be `col=col`, to handle this, inject 2 projections.
+				_, isCol0 := newSf.GetArgs()[0].(*expression.Column)
+				_, isCol1 := newSf.GetArgs()[1].(*expression.Column)
+				if !isCol0 || !isCol1 {
+					if !isCol0 {
+						leftPlan, rCol = s.injectExpr(leftPlan, newSf.GetArgs()[0])
+					}
+					if !isCol1 {
+						rightPlan, lCol = s.injectExpr(rightPlan, newSf.GetArgs()[1])
+					}
+					leftNode, rightNode = leftPlan, rightPlan
+					newSf = expression.NewFunctionInternal(s.ctx.GetExprCtx(), ast.EQ, edge.GetType(),
+						rCol, lCol).(*expression.ScalarFunction)
+				}
 				usedEdges = append(usedEdges, newSf)
 			}
 		}
 	}
 	return
 }
 
+func (s *baseSingleGroupJoinOrderSolver) injectExpr(p base.LogicalPlan, expr expression.Expression) (base.LogicalPlan, *expression.Column) {
+	proj, ok := p.(*LogicalProjection)
+	if !ok {
+		proj = LogicalProjection{Exprs: cols2Exprs(p.Schema().Columns)}.Init(p.SCtx(), p.QueryBlockOffset())
+		proj.SetSchema(p.Schema().Clone())
+		proj.SetChildren(p)
+	}
+	return proj, proj.appendExpr(expr)
+}
+
 // makeJoin build join tree for the nodes which have equal conditions to connect them.
 func (s *baseSingleGroupJoinOrderSolver) makeJoin(leftPlan, rightPlan base.LogicalPlan, eqEdges []*expression.ScalarFunction, joinType *joinTypeWithExtMsg) (base.LogicalPlan, []expression.Expression) {
 	remainOtherConds := make([]expression.Expression, len(s.otherConds))