From 4a8d083515da4fc7d02f8788a0a396ed459fe940 Mon Sep 17 00:00:00 2001
From: bb7133 <bb7133@gmail.com>
Date: Thu, 4 Jul 2019 17:04:17 +0800
Subject: [PATCH] ddl: allow more charset/collation modifications for
 database/table (#10958)

---
 ddl/db_integration_test.go | 31 +++++++++++++++++++------------
 ddl/ddl_api.go             |  6 ++++--
 2 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/ddl/db_integration_test.go b/ddl/db_integration_test.go
index 35297e8327731..f272116f30be0 100644
--- a/ddl/db_integration_test.go
+++ b/ddl/db_integration_test.go
@@ -319,17 +319,17 @@ func (s *testIntegrationSuite) TestChangingTableCharset(c *C) {
 	tk.MustExec("drop table t;")
 	tk.MustExec("create table t(a varchar(10)) charset utf8")
 	tk.MustExec("alter table t convert to charset utf8mb4;")
-	checkCharset := func() {
+	checkCharset := func(chs, coll string) {
 		tbl := testGetTableByName(c, tk.Se, "test", "t")
 		c.Assert(tbl, NotNil)
-		c.Assert(tbl.Meta().Charset, Equals, charset.CharsetUTF8MB4)
-		c.Assert(tbl.Meta().Collate, Equals, charset.CollationUTF8MB4)
+		c.Assert(tbl.Meta().Charset, Equals, chs)
+		c.Assert(tbl.Meta().Collate, Equals, coll)
 		for _, col := range tbl.Meta().Columns {
-			c.Assert(col.Charset, Equals, charset.CharsetUTF8MB4)
-			c.Assert(col.Collate, Equals, charset.CollationUTF8MB4)
+			c.Assert(col.Charset, Equals, chs)
+			c.Assert(col.Collate, Equals, coll)
 		}
 	}
-	checkCharset()
+	checkCharset(charset.CharsetUTF8MB4, charset.CollationUTF8MB4)
 
 	// Test when column charset can not convert to the target charset.
 	tk.MustExec("drop table t;")
@@ -338,11 +338,16 @@ func (s *testIntegrationSuite) TestChangingTableCharset(c *C) {
 	c.Assert(err, NotNil)
 	c.Assert(err.Error(), Equals, "[ddl:210]unsupported modify charset from ascii to utf8mb4")
 
+	tk.MustExec("drop table t;")
+	tk.MustExec("create table t(a varchar(10) character set utf8) charset utf8")
+	tk.MustExec("alter table t convert to charset utf8 collate utf8_general_ci;")
+	checkCharset(charset.CharsetUTF8, "utf8_general_ci")
+
 	// Test when table charset is equal to target charset but column charset is not equal.
 	tk.MustExec("drop table t;")
 	tk.MustExec("create table t(a varchar(10) character set utf8) charset utf8mb4")
-	tk.MustExec("alter table t convert to charset utf8mb4;")
-	checkCharset()
+	tk.MustExec("alter table t convert to charset utf8mb4 collate utf8mb4_general_ci;")
+	checkCharset(charset.CharsetUTF8MB4, "utf8mb4_general_ci")
 
 	// Mock table info with charset is "". Old TiDB maybe create table with charset is "".
 	db, ok := domain.GetDomain(tk.Se).InfoSchema().SchemaByName(model.NewCIStr("test"))
@@ -375,7 +380,7 @@ func (s *testIntegrationSuite) TestChangingTableCharset(c *C) {
 	c.Assert(tbl.Meta().Collate, Equals, "")
 	// Test when table charset is "", this for compatibility.
 	tk.MustExec("alter table t convert to charset utf8mb4;")
-	checkCharset()
+	checkCharset(charset.CharsetUTF8MB4, charset.CollationUTF8MB4)
 
 	// Test when column charset is "".
 	tbl = testGetTableByName(c, tk.Se, "test", "t")
@@ -390,7 +395,7 @@ func (s *testIntegrationSuite) TestChangingTableCharset(c *C) {
 	c.Assert(tbl.Meta().Columns[0].Charset, Equals, "")
 	c.Assert(tbl.Meta().Columns[0].Collate, Equals, "")
 	tk.MustExec("alter table t convert to charset utf8mb4;")
-	checkCharset()
+	checkCharset(charset.CharsetUTF8MB4, charset.CollationUTF8MB4)
 
 	tk.MustExec("drop table t")
 	tk.MustExec("create table t (a blob) character set utf8;")
@@ -743,10 +748,12 @@ func (s *testIntegrationSuite) TestChangingDBCharset(c *C) {
 		_, err := tk.Exec(fc.stmt)
 		c.Assert(err.Error(), Equals, fc.errMsg, Commentf("%v", fc.stmt))
 	}
+	tk.MustExec("ALTER SCHEMA CHARACTER SET = 'utf8' COLLATE = 'utf8_unicode_ci'")
+	verifyDBCharsetAndCollate("alterdb2", "utf8", "utf8_unicode_ci")
 
 	tk.MustExec("ALTER SCHEMA CHARACTER SET = 'utf8mb4'")
 	verifyDBCharsetAndCollate("alterdb2", "utf8mb4", "utf8mb4_bin")
 
-	_, err := tk.Exec("ALTER SCHEMA CHARACTER SET = 'utf8mb4' COLLATE = 'utf8mb4_general_ci'")
-	c.Assert(err.Error(), Equals, "[ddl:210]unsupported modify collate from utf8mb4_bin to utf8mb4_general_ci")
+	tk.MustExec("ALTER SCHEMA CHARACTER SET = 'utf8mb4' COLLATE = 'utf8mb4_general_ci'")
+	verifyDBCharsetAndCollate("alterdb2", "utf8mb4", "utf8mb4_general_ci")
 }
diff --git a/ddl/ddl_api.go b/ddl/ddl_api.go
index 8f7a4f04b8b24..9b4d3cde8b127 100644
--- a/ddl/ddl_api.go
+++ b/ddl/ddl_api.go
@@ -1759,8 +1759,10 @@ func modifiableCharsetAndCollation(toCharset, toCollate, origCharset, origCollat
 	if !charset.ValidCharsetAndCollation(toCharset, toCollate) {
 		return ErrUnknownCharacterSet.GenWithStack("Unknown character set: '%s', collation: '%s'", toCharset, toCollate)
 	}
-	if toCharset == charset.CharsetUTF8MB4 && origCharset == charset.CharsetUTF8 {
-		// TiDB only allow utf8 to be changed to utf8mb4.
+	if (origCharset == charset.CharsetUTF8 && toCharset == charset.CharsetUTF8MB4) ||
+		(origCharset == charset.CharsetUTF8 && toCharset == charset.CharsetUTF8) ||
+		(origCharset == charset.CharsetUTF8MB4 && toCharset == charset.CharsetUTF8MB4) {
+		// TiDB only allow utf8 to be changed to utf8mb4, or changing the collation when the charset is utf8/utf8mb4.
 		return nil
 	}