From df908bf31f2532810737fb8f22fdb6fa32237ee9 Mon Sep 17 00:00:00 2001
From: Chengpeng Yan <41809508+Reminiscent@users.noreply.github.com>
Date: Mon, 2 Aug 2021 16:57:06 +0800
Subject: [PATCH] planner: add binding info for explain stmt (#26403)

---
 bindinfo/bind_test.go | 18 ++++++++++++++++++
 planner/optimize.go   | 12 +++++++++++-
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/bindinfo/bind_test.go b/bindinfo/bind_test.go
index 6e0b341d76..256c1be1ec 100644
--- a/bindinfo/bind_test.go
+++ b/bindinfo/bind_test.go
@@ -1891,6 +1891,24 @@ func (s *testSuite) TestReCreateBind(c *C) {
 	c.Assert(rows[0][3], Equals, "using")
 }
 
+func (s *testSuite) TestExplainShowBindSQL(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	s.cleanBindingEnv(tk)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a int, b int, key(a))")
+
+	tk.MustExec("create global binding for select * from t using select * from t use index(a)")
+	tk.MustQuery("select original_sql, bind_sql from mysql.bind_info where default_db != 'mysql'").Check(testkit.Rows(
+		"select * from `test` . `t` SELECT * FROM `test`.`t` USE INDEX (`a`)",
+	))
+
+	tk.MustExec("explain select * from t")
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1105 Using the bindSQL: SELECT * FROM `test`.`t` USE INDEX (`a`)"))
+	tk.MustExec("explain analyze select * from t")
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1105 Using the bindSQL: SELECT * FROM `test`.`t` USE INDEX (`a`)"))
+}
+
 func (s *testSuite) TestDMLIndexHintBind(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	s.cleanBindingEnv(tk)
diff --git a/planner/optimize.go b/planner/optimize.go
index 8fbd1d3782..64afe1b329 100644
--- a/planner/optimize.go
+++ b/planner/optimize.go
@@ -170,11 +170,17 @@ func Optimize(ctx context.Context, sctx sessionctx.Context, node ast.Node, is in
 	if binding != nil && binding.Status == bindinfo.Using {
 		if sctx.GetSessionVars().UsePlanBaselines {
 			stmtHints, warns = handleStmtHints(binding.Hint.GetFirstTableHints())
+			if _, ok := stmtNode.(*ast.ExplainStmt); ok {
+				sctx.GetSessionVars().StmtCtx.AppendWarning(errors.Errorf("Using the bindSQL: %v", binding.BindSQL))
+			}
 		}
 		return bestPlan, names, nil
 	}
 	bestCostAmongHints := math.MaxFloat64
-	var bestPlanAmongHints plannercore.Plan
+	var (
+		bestPlanAmongHints plannercore.Plan
+		bestPlanBindSQL    string
+	)
 	originHints := hint.CollectHint(stmtNode)
 	// Try to find the best binding.
 	for _, binding := range bindRecord.Bindings {
@@ -201,8 +207,12 @@ func Optimize(ctx context.Context, sctx sessionctx.Context, node ast.Node, is in
 			}
 			bestCostAmongHints = cost
 			bestPlanAmongHints = plan
+			bestPlanBindSQL = binding.BindSQL
 		}
 	}
+	if _, ok := stmtNode.(*ast.ExplainStmt); ok && bestPlanBindSQL != "" {
+		sctx.GetSessionVars().StmtCtx.AppendWarning(errors.Errorf("Using the bindSQL: %v", bestPlanBindSQL))
+	}
 	// 1. If it is a select query.
 	// 2. If there is already a evolution task, we do not need to handle it again.
 	// 3. If the origin binding contain `read_from_storage` hint, we should ignore the evolve task.