From b3d7a8e85fb0b4fe44a536e5bfdb8b358174a324 Mon Sep 17 00:00:00 2001
From: e11jah <30852919+e11jah@users.noreply.github.com>
Date: Mon, 30 May 2022 13:58:26 +0800
Subject: [PATCH] executor: fix show database like case sensitive issue#34766
 (#34925)

close pingcap/tidb#34766
---
 executor/show.go                         | 19 +++++++++++++++++++
 executor/show_test.go                    | 17 +++++++++++++++++
 planner/core/planbuilder.go              |  7 +++++++
 planner/core/show_predicate_extractor.go | 23 +++++++++++++++++++++++
 planner/core/stringer_test.go            | 16 ++++++++++++++++
 5 files changed, 82 insertions(+)

diff --git a/executor/show.go b/executor/show.go
index 79d466aa71d2e..d4568e86526cb 100644
--- a/executor/show.go
+++ b/executor/show.go
@@ -402,11 +402,30 @@ func (e *ShowExec) fetchShowDatabases() error {
 	dbs := e.is.AllSchemaNames()
 	checker := privilege.GetPrivilegeManager(e.ctx)
 	sort.Strings(dbs)
+	var (
+		fieldPatternsLike collate.WildcardPattern
+		FieldFilterEnable bool
+		fieldFilter       string
+	)
+
+	if e.Extractor != nil {
+		extractor := (e.Extractor).(*plannercore.ShowDatabaseExtractor)
+		if extractor.FieldPatterns != "" {
+			fieldPatternsLike = collate.GetCollatorByID(collate.CollationName2ID(mysql.UTF8MB4DefaultCollation)).Pattern()
+			fieldPatternsLike.Compile(extractor.FieldPatterns, byte('\\'))
+		}
+		FieldFilterEnable = extractor.Field != ""
+		fieldFilter = extractor.Field
+	}
 	// let information_schema be the first database
 	moveInfoSchemaToFront(dbs)
 	for _, d := range dbs {
 		if checker != nil && !checker.DBIsVisible(e.ctx.GetSessionVars().ActiveRoles, d) {
 			continue
+		} else if FieldFilterEnable && strings.ToLower(d) != fieldFilter {
+			continue
+		} else if fieldPatternsLike != nil && !fieldPatternsLike.DoMatch(strings.ToLower(d)) {
+			continue
 		}
 		e.appendRow([]interface{}{
 			d,
diff --git a/executor/show_test.go b/executor/show_test.go
index e4e45bb4b9bb6..a1e511785b9b1 100644
--- a/executor/show_test.go
+++ b/executor/show_test.go
@@ -1831,3 +1831,20 @@ func TestShowBindingCacheStatus(t *testing.T) {
 	tk.MustQuery("show binding_cache status").Check(testkit.Rows(
 		"1 1 198 Bytes 250 Bytes"))
 }
+
+func TestShowDatabasesLike(t *testing.T) {
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+
+	tk := testkit.NewTestKit(t, store)
+	require.True(t, tk.Session().Auth(&auth.UserIdentity{
+		Username: "root", Hostname: "%"}, nil, nil))
+
+	tk.MustExec("DROP DATABASE IF EXISTS `TEST_$1`")
+	tk.MustExec("DROP DATABASE IF EXISTS `test_$2`")
+	tk.MustExec("CREATE DATABASE `TEST_$1`;")
+	tk.MustExec("CREATE DATABASE `test_$2`;")
+
+	tk.MustQuery("SHOW DATABASES LIKE 'TEST_%'").Check(testkit.Rows("TEST_$1", "test_$2"))
+	tk.MustQuery("SHOW DATABASES LIKE 'test_%'").Check(testkit.Rows("TEST_$1", "test_$2"))
+}
diff --git a/planner/core/planbuilder.go b/planner/core/planbuilder.go
index 5f73a1b8778a4..22f105d9fe6c1 100644
--- a/planner/core/planbuilder.go
+++ b/planner/core/planbuilder.go
@@ -3012,6 +3012,13 @@ func (b *PlanBuilder) buildShow(ctx context.Context, show *ast.ShowStmt) (Plan,
 		if tableInfo.Meta().TempTableType != model.TempTableNone {
 			return nil, ErrOptOnTemporaryTable.GenWithStackByArgs("show table regions")
 		}
+	case ast.ShowDatabases:
+		var extractor ShowDatabaseExtractor
+		if extractor.Extract(show) {
+			p.Extractor = &extractor
+			// Avoid building Selection.
+			show.Pattern = nil
+		}
 	}
 	if show.Tp == ast.ShowVariables {
 		var extractor ShowVariablesExtractor
diff --git a/planner/core/show_predicate_extractor.go b/planner/core/show_predicate_extractor.go
index 352b38b4f8b8c..eb9806c44ee5c 100644
--- a/planner/core/show_predicate_extractor.go
+++ b/planner/core/show_predicate_extractor.go
@@ -28,6 +28,7 @@ var (
 	_ ShowPredicateExtractor = &ShowColumnsTableExtractor{}
 	_ ShowPredicateExtractor = &ShowTablesTableExtractor{}
 	_ ShowPredicateExtractor = &ShowVariablesExtractor{}
+	_ ShowPredicateExtractor = &ShowDatabaseExtractor{}
 )
 
 // ShowPredicateExtractor is used to extract some predicates from `PatternLikeExpr` clause
@@ -167,3 +168,25 @@ func (e *ShowVariablesExtractor) explainInfo() string {
 	}
 	return s
 }
+
+// ShowDatabaseExtractor is used to extract some predicates of databases.
+type ShowDatabaseExtractor struct {
+	ShowBaseExtractor
+}
+
+func (e *ShowDatabaseExtractor) explainInfo() string {
+	r := new(bytes.Buffer)
+	if len(e.Field) > 0 {
+		r.WriteString(fmt.Sprintf("database:[%s], ", e.Field))
+	}
+	if len(e.FieldPatterns) > 0 {
+		r.WriteString(fmt.Sprintf("database_pattern:[%s], ", e.FieldPatterns))
+	}
+
+	// remove the last ", " in the message info
+	s := r.String()
+	if len(s) > 2 {
+		return s[:len(s)-2]
+	}
+	return s
+}
diff --git a/planner/core/stringer_test.go b/planner/core/stringer_test.go
index 6433ad59b158c..374c0589694ca 100644
--- a/planner/core/stringer_test.go
+++ b/planner/core/stringer_test.go
@@ -72,6 +72,22 @@ func TestPlanStringer(t *testing.T) {
 			sql:  "show tables in test like '%T%'",
 			plan: "Show(table_pattern:[%t%])",
 		},
+		{
+			sql:  "show databases like 't'",
+			plan: "Show(database:[t])",
+		},
+		{
+			sql:  "show databases like 'T'",
+			plan: "Show(database:[t])",
+		},
+		{
+			sql:  "show databases like 't%'",
+			plan: "Show(database_pattern:[t%])",
+		},
+		{
+			sql:  "show databases like '%T%'",
+			plan: "Show(database_pattern:[%t%])",
+		},
 	}
 	parser := parser.New()
 	for _, tt := range tests {