use @@session.collation_server during create database ...

enginetest/queries/charset_collation_engine.go

@@ -452,6 +452,118 @@ var CharsetCollationEngineTests = []CharsetCollationEngineTest{
 			},
 		},
 	},
+	{
+		Name: "setting charset/collation sets the other",
+		Queries: []CharsetCollationEngineTestQuery{
+			{
+				Query: "select @@session.character_set_connection, @@session.collation_connection;",
+				Expected: []sql.Row{
+					{"utf8mb4", "utf8mb4_0900_bin"},
+				},
+			},
+			{
+				Query:    "set @@session.character_set_connection = 'latin1';",
+				Expected: []sql.Row{{}},
+			},
+			{
+				Query: "select @@session.character_set_connection, @@session.collation_connection;",
+				Expected: []sql.Row{
+					{"latin1", "latin1_swedish_ci"},
+				},
+			},
+			{
+				Query:    "set @@session.collation_connection = 'utf8mb4_0900_bin';",
+				Expected: []sql.Row{{}},
+			},
+			{
+				Query: "select @@session.character_set_connection, @@session.collation_connection;",
+				Expected: []sql.Row{
+					{"utf8mb4", "utf8mb4_0900_bin"},
+				},
+			},
+
+			{
+				Query: "select @@global.character_set_connection, @@global.collation_connection;",
+				Expected: []sql.Row{
+					{"utf8mb4", "utf8mb4_0900_bin"},
+				},
+			},
+			{
+				Query:    "set @@global.character_set_connection = 'latin1';",
+				Expected: []sql.Row{{}},
+			},
+			{
+				Query: "select @@global.character_set_connection, @@global.collation_connection;",
+				Expected: []sql.Row{
+					{"latin1", "latin1_swedish_ci"},
+				},
+			},
+			{
+				Query:    "set @@global.collation_connection = 'utf8mb4_0900_bin';",
+				Expected: []sql.Row{{}},
+			},
+			{
+				Query: "select @@global.character_set_connection, @@global.collation_connection;",
+				Expected: []sql.Row{
+					{"utf8mb4", "utf8mb4_0900_bin"},
+				},
+			},
+
+			{
+				Query: "select @@session.character_set_server, @@session.collation_server;",
+				Expected: []sql.Row{
+					{"utf8mb4", "utf8mb4_0900_bin"},
+				},
+			},
+			{
+				Query:    "set @@session.character_set_server = 'latin1';",
+				Expected: []sql.Row{{}},
+			},
+			{
+				Query: "select @@session.character_set_server, @@session.collation_server;",
+				Expected: []sql.Row{
+					{"latin1", "latin1_swedish_ci"},
+				},
+			},
+			{
+				Query:    "set @@session.collation_server = 'utf8mb4_0900_bin';",
+				Expected: []sql.Row{{}},
+			},
+			{
+				Query: "select @@session.character_set_server, @@session.collation_server;",
+				Expected: []sql.Row{
+					{"utf8mb4", "utf8mb4_0900_bin"},
+				},
+			},
+
+			{
+				Query: "select @@global.character_set_server, @@global.collation_server;",
+				Expected: []sql.Row{
+					{"utf8mb4", "utf8mb4_0900_bin"},
+				},
+			},
+			{
+				Query:    "set @@global.character_set_server = 'latin1';",
+				Expected: []sql.Row{{}},
+			},
+			{
+				Query: "select @@global.character_set_server, @@global.collation_server;",
+				Expected: []sql.Row{
+					{"latin1", "latin1_swedish_ci"},
+				},
+			},
+			{
+				Query:    "set @@global.collation_server = 'utf8mb4_0900_bin';",
+				Expected: []sql.Row{{}},
+			},
+			{
+				Query: "select @@global.character_set_server, @@global.collation_server;",
+				Expected: []sql.Row{
+					{"utf8mb4", "utf8mb4_0900_bin"},
+				},
+			},
+		},
+	},
 	{
 		Name: "ENUM collation handling",
 		SetUpScript: []string{

enginetest/queries/script_queries.go

@@ -6302,6 +6302,34 @@ where
 			},
 		},
 	},
+	{
+		Name: "test create database with modified server variables",
+		SetUpScript: []string{
+			"set @@session.character_set_server = 'latin1';",
+			"create database latin1_db;",
+		},
+		Assertions: []ScriptTestAssertion{
+			{
+				Query: "select @@global.character_set_server, @@global.collation_server;",
+				Expected: []sql.Row{
+					{"utf8mb4", "utf8mb4_0900_bin"},
+				},
+			},
+			{
+				Query: "select @@session.character_set_server, @@session.collation_server;",
+				Expected: []sql.Row{
+					{"latin1", "latin1_swedish_ci"},
+				},
+			},
+			{
+				// Interestingly, session actually takes priority over global
+				Query: "show create database latin1_db",
+				Expected: []sql.Row{
+					{"latin1_db", "CREATE DATABASE `latin1_db` /*!40100 DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci */"},
+				},
+			},
+		},
+	},
 }
 
 var SpatialScriptTests = []ScriptTest{

sql/planbuilder/ddl.go

@@ -1496,6 +1496,14 @@ func (b *Builder) buildDBDDL(inScope *scope, c *ast.DBDDL) (outScope *scope) {
 				collationStr = cc.Value
 			}
 		}
+		// TODO: ensure that collation and charset match when setting them
+		if len(charsetStr) == 0 && len(collationStr) == 0 {
+			collation, err := b.ctx.Session.GetSessionVariable(b.ctx, "collation_server")
+			if err != nil {
+				b.handleErr(err)
+			}
+			collationStr = collation.(string)
+		}
 		collation, err := sql.ParseCollation(charsetStr, collationStr, false)
 		if err != nil {
 			b.handleErr(err)

sql/rowexec/rel_iters.go

@@ -633,33 +633,70 @@ func setSystemVar(ctx *sql.Context, sysVar *expression.SystemVar, right sql.Expr
 	if err != nil {
 		return err
 	}
-	// Setting `character_set_connection`, regardless of how it is set (directly or through SET NAMES) will also set
-	// `collation_connection` to the default collation for the given character set.
-	if strings.ToLower(sysVar.Name) == "character_set_connection" {
-		newSysVar := &expression.SystemVar{
-			Name:  "collation_connection",
-			Scope: sysVar.Scope,
+
+	// Setting `character_set_connection` and `collation_connection` will set the corresponding variable
+	// Setting `character_set_server` and `collation_server` will set the corresponding variable
+	switch strings.ToLower(sysVar.Name) {
+	case "character_set_connection":
+		if val == nil {
+			return sysVar.Scope.SetValue(ctx, "collation_connection", val)
 		}
+		valStr, ok := val.(string)
+		if !ok {
+			return sql.ErrInvalidSystemVariableValue.New("collation_connection", val)
+		}
+		var charset sql.CharacterSetID
+		charset, err = sql.ParseCharacterSet(valStr)
+		if err != nil {
+			return err
+		}
+		collationName := charset.DefaultCollation().Name()
+		return sysVar.Scope.SetValue(ctx, "collation_connection", collationName)
+	case "collation_connection":
 		if val == nil {
-			err = setSystemVar(ctx, newSysVar, expression.NewLiteral("", types.LongText), row)
-			if err != nil {
-				return err
-			}
-		} else {
-			valStr, ok := val.(string)
-			if !ok {
-				return sql.ErrInvalidSystemVariableValue.New("collation_connection", val)
-			}
-			charset, err := sql.ParseCharacterSet(valStr)
-			if err != nil {
-				return err
-			}
-			charset = charset
-			err = setSystemVar(ctx, newSysVar, expression.NewLiteral(charset.DefaultCollation().Name(), types.LongText), row)
-			if err != nil {
-				return err
-			}
+			return sysVar.Scope.SetValue(ctx, "character_set_connection", val)
+		}
+		valStr, ok := val.(string)
+		if !ok {
+			return sql.ErrInvalidSystemVariableValue.New("character_set_connection", val)
+		}
+		var collation sql.CollationID
+		collation, err = sql.ParseCollation("", valStr, false)
+		if err != nil {
+			return err
+		}
+		charsetName := collation.CharacterSet().Name()
+		return sysVar.Scope.SetValue(ctx, "character_set_connection", charsetName)
+	case "character_set_server":
+		if val == nil {
+			return sysVar.Scope.SetValue(ctx, "collation_server", val)
+		}
+		valStr, ok := val.(string)
+		if !ok {
+			return sql.ErrInvalidSystemVariableValue.New("collation_server", val)
+		}
+		var charset sql.CharacterSetID
+		charset, err = sql.ParseCharacterSet(valStr)
+		if err != nil {
+			return err
+		}
+		collationName := charset.DefaultCollation().Name()
+		return sysVar.Scope.SetValue(ctx, "collation_server", collationName)
+	case "collation_server":
+		if val == nil {
+			return sysVar.Scope.SetValue(ctx, "character_set_server", val)
+		}
+		valStr, ok := val.(string)
+		if !ok {
+			return sql.ErrInvalidSystemVariableValue.New("character_set_server", val)
+		}
+		var collation sql.CollationID
+		collation, err = sql.ParseCollation("", valStr, false)
+		if err != nil {
+			return err
 		}
+		charsetName := collation.CharacterSet().Name()
+		return sysVar.Scope.SetValue(ctx, "character_set_server", charsetName)
 	}
 	return nil
 }

sql/session.go

@@ -36,8 +36,9 @@ const (
 )
 
 const (
-	CurrentDBSessionVar              = "current_database"
-	AutoCommitSessionVar             = "autocommit"
+	CurrentDBSessionVar  = "current_database"
+	AutoCommitSessionVar = "autocommit"
+	// TODO: how does character set and collation get matched?
 	characterSetConnectionSysVarName = "character_set_connection"
 	characterSetResultsSysVarName    = "character_set_results"
 	collationConnectionSysVarName    = "collation_connection"