MDEV-307 Add functionality for database comments

This commit adds a new feature to the server to add comments at the database
level. 1024 bytes is the maximum comment length allowed. If the comment length
exceeds this limit, a new error/warning code 4144 is thrown, based on whether
thd->is_strict_mode() is true/false. The database comment is also added to the
db.opt file, as well as to the information_schema.schemata table.

include/mysql_com.h

@@ -71,6 +71,7 @@
 #define COLUMN_COMMENT_MAXLEN 1024
 #define INDEX_COMMENT_MAXLEN 1024
 #define TABLE_PARTITION_COMMENT_MAXLEN 1024
+#define DATABASE_COMMENT_MAXLEN 1024
 
 /*
   Maximum length of protocol packet.

mysql-test/main/comment_database.test

+--echo #
+--echo # MDEV-307: Add functionality for database comments
+--echo #
+
+# Check an error state
+--error ER_PARSE_ERROR
+CREATE DATABASE db1 COMMENT=;
+
+# 1024 bytes
+CREATE DATABASE db1
+COMMENT='abcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcd';
+SHOW CREATE DATABASE db1;
+SELECT schema_comment, char_length(schema_comment)
+FROM information_schema.schemata
+WHERE schema_name='db1';
+DROP DATABASE db1;
+
+# 1025 bytes (warning)
+SET SQL_MODE='';
+CREATE DATABASE db1
+COMMENT='abcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcde';
+SHOW CREATE DATABASE db1;
+SELECT schema_comment, char_length(schema_comment)
+FROM information_schema.schemata
+WHERE schema_name='db1';
+DROP DATABASE db1;
+SET SQL_MODE='TRADITIONAL';
+
+# 1025 bytes (error)
+--error ER_TOO_LONG_DATABASE_COMMENT
+CREATE DATABASE db1
+COMMENT='abcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcde';
+SELECT schema_comment, char_length(schema_comment)
+FROM information_schema.schemata
+WHERE schema_name='db1';
+
+CREATE DATABASE db1 COMMENT 'db1';
+SHOW CREATE DATABASE db1;
+ALTER DATABASE db1 COMMENT = "db1 comment";
+SELECT * FROM information_schema.schemata
+WHERE schema_name='db1';
+DROP DATABASE db1;
+
+CREATE DATABASE db1;
+USE db1;
+ALTER DATABASE COMMENT 'db1 comment' CHARACTER SET 'utf8';
+SHOW CREATE DATABASE db1;
+ALTER DATABASE db1 COMMENT 'this is db1 comment';
+SHOW CREATE DATABASE db1;
+ALTER DATABASE CHARACTER SET 'latin1';
+SHOW CREATE DATABASE db1;
+DROP DATABASE db1;
+
+# Test the case when the database is named 'comment'
+CREATE DATABASE comment COMMENT 'comment' CHARACTER SET 'latin2';
+SHOW CREATE DATABASE comment;
+ALTER DATABASE comment COMMENT 'comment comment';
+SHOW CREATE DATABASE comment;
+USE comment;
+ALTER DATABASE COMMENT 'comment';
+SELECT * FROM information_schema.schemata
+WHERE schema_name='comment';
+DROP DATABASE comment;

mysql-test/main/information_schema.result

@@ -10,11 +10,11 @@ grant select, update on test.* to mysqltest_1@localhost;
 create user mysqltest_3@localhost;
 create user mysqltest_3;
 select * from information_schema.SCHEMATA where schema_name > 'm';
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
-def	mtr	latin1	latin1_swedish_ci	NULL
-def	mysql	latin1	latin1_swedish_ci	NULL
-def	performance_schema	utf8	utf8_general_ci	NULL
-def	test	latin1	latin1_swedish_ci	NULL
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
+def	mtr	latin1	latin1_swedish_ci	NULL	
+def	mysql	latin1	latin1_swedish_ci	NULL	
+def	performance_schema	utf8	utf8_general_ci	NULL	
+def	test	latin1	latin1_swedish_ci	NULL	
 select schema_name from information_schema.schemata;
 schema_name
 information_schema
@@ -1575,14 +1575,14 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	b	ALL	NULL	NULL	NULL	NULL	NULL	Using where; Open_frm_only; Scanned all databases; Using join buffer (flat, BNL join)
 SELECT * FROM INFORMATION_SCHEMA.SCHEMATA
 WHERE SCHEMA_NAME = 'mysqltest';
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
 SELECT * FROM INFORMATION_SCHEMA.SCHEMATA
 WHERE SCHEMA_NAME = '';
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
 SELECT * FROM INFORMATION_SCHEMA.SCHEMATA
 WHERE SCHEMA_NAME = 'test';
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
-def	test	latin1	latin1_swedish_ci	NULL
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
+def	test	latin1	latin1_swedish_ci	NULL	
 select count(*) from INFORMATION_SCHEMA.TABLES where TABLE_SCHEMA='mysql' AND TABLE_NAME='nonexisting';
 count(*)
 0
@@ -1627,7 +1627,7 @@ CONSTRAINT_CATALOG	CONSTRAINT_SCHEMA	CONSTRAINT_NAME	UNIQUE_CONSTRAINT_CATALOG	U
 select * from `information_schema`.`REFERENTIAL_CONSTRAINTS` where `TABLE_NAME` = NULL;
 CONSTRAINT_CATALOG	CONSTRAINT_SCHEMA	CONSTRAINT_NAME	UNIQUE_CONSTRAINT_CATALOG	UNIQUE_CONSTRAINT_SCHEMA	UNIQUE_CONSTRAINT_NAME	MATCH_OPTION	UPDATE_RULE	DELETE_RULE	TABLE_NAME	REFERENCED_TABLE_NAME
 select * from information_schema.schemata where schema_name = NULL;
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
 select * from `information_schema`.`STATISTICS` where `TABLE_SCHEMA` = NULL;
 TABLE_CATALOG	TABLE_SCHEMA	TABLE_NAME	NON_UNIQUE	INDEX_SCHEMA	INDEX_NAME	SEQ_IN_INDEX	COLUMN_NAME	COLLATION	CARDINALITY	SUB_PART	PACKED	NULLABLE	INDEX_TYPE	COMMENT	INDEX_COMMENT
 select * from `information_schema`.`STATISTICS` where `TABLE_NAME` = NULL;

mysql-test/suite/funcs_1/r/is_columns_is.result

@@ -326,6 +326,7 @@ def	information_schema	ROUTINES	SQL_PATH	22	NULL	YES	varchar	64	192	NULL	NULL	NU
 def	information_schema	SCHEMATA	CATALOG_NAME	1	''	NO	varchar	512	1536	NULL	NULL	NULL	utf8	utf8_general_ci	varchar(512)			select		NEVER	NULL
 def	information_schema	SCHEMATA	DEFAULT_CHARACTER_SET_NAME	3	''	NO	varchar	32	96	NULL	NULL	NULL	utf8	utf8_general_ci	varchar(32)			select		NEVER	NULL
 def	information_schema	SCHEMATA	DEFAULT_COLLATION_NAME	4	''	NO	varchar	32	96	NULL	NULL	NULL	utf8	utf8_general_ci	varchar(32)			select		NEVER	NULL
+def	information_schema	SCHEMATA	SCHEMA_COMMENT	6	''	NO	varchar	1024	3072	NULL	NULL	NULL	utf8	utf8_general_ci	varchar(1024)			select		NEVER	NULL
 def	information_schema	SCHEMATA	SCHEMA_NAME	2	''	NO	varchar	64	192	NULL	NULL	NULL	utf8	utf8_general_ci	varchar(64)			select		NEVER	NULL
 def	information_schema	SCHEMATA	SQL_PATH	5	NULL	YES	varchar	512	1536	NULL	NULL	NULL	utf8	utf8_general_ci	varchar(512)			select		NEVER	NULL
 def	information_schema	SCHEMA_PRIVILEGES	GRANTEE	1	''	NO	varchar	190	570	NULL	NULL	NULL	utf8	utf8_general_ci	varchar(190)			select		NEVER	NULL
@@ -870,6 +871,7 @@ NULL	information_schema	ROUTINES	LAST_ALTERED	datetime	NULL	NULL	NULL	NULL	datet
 3.0000	information_schema	SCHEMATA	DEFAULT_CHARACTER_SET_NAME	varchar	32	96	utf8	utf8_general_ci	varchar(32)
 3.0000	information_schema	SCHEMATA	DEFAULT_COLLATION_NAME	varchar	32	96	utf8	utf8_general_ci	varchar(32)
 3.0000	information_schema	SCHEMATA	SQL_PATH	varchar	512	1536	utf8	utf8_general_ci	varchar(512)
+3.0000	information_schema	SCHEMATA	SCHEMA_COMMENT	varchar	1024	3072	utf8	utf8_general_ci	varchar(1024)
 3.0000	information_schema	SCHEMA_PRIVILEGES	GRANTEE	varchar	190	570	utf8	utf8_general_ci	varchar(190)
 3.0000	information_schema	SCHEMA_PRIVILEGES	TABLE_CATALOG	varchar	512	1536	utf8	utf8_general_ci	varchar(512)
 3.0000	information_schema	SCHEMA_PRIVILEGES	TABLE_SCHEMA	varchar	64	192	utf8	utf8_general_ci	varchar(64)

mysql-test/suite/funcs_1/r/is_schemata.result

@@ -33,6 +33,7 @@ SCHEMA_NAME	varchar(64)	NO
 DEFAULT_CHARACTER_SET_NAME	varchar(32)	NO			
 DEFAULT_COLLATION_NAME	varchar(32)	NO			
 SQL_PATH	varchar(512)	YES		NULL	
+SCHEMA_COMMENT	varchar(1024)	NO			
 SHOW CREATE TABLE information_schema.SCHEMATA;
 Table	Create Table
 SCHEMATA	CREATE TEMPORARY TABLE `SCHEMATA` (
@@ -40,7 +41,8 @@ SCHEMATA	CREATE TEMPORARY TABLE `SCHEMATA` (
   `SCHEMA_NAME` varchar(64) NOT NULL DEFAULT '',
   `DEFAULT_CHARACTER_SET_NAME` varchar(32) NOT NULL DEFAULT '',
   `DEFAULT_COLLATION_NAME` varchar(32) NOT NULL DEFAULT '',
-  `SQL_PATH` varchar(512) DEFAULT NULL
+  `SQL_PATH` varchar(512) DEFAULT NULL,
+  `SCHEMA_COMMENT` varchar(1024) NOT NULL DEFAULT ''
 ) ENGINE=MEMORY DEFAULT CHARSET=utf8
 SHOW COLUMNS FROM information_schema.SCHEMATA;
 Field	Type	Null	Key	Default	Extra
@@ -49,6 +51,7 @@ SCHEMA_NAME	varchar(64)	NO
 DEFAULT_CHARACTER_SET_NAME	varchar(32)	NO			
 DEFAULT_COLLATION_NAME	varchar(32)	NO			
 SQL_PATH	varchar(512)	YES		NULL	
+SCHEMA_COMMENT	varchar(1024)	NO			
 SELECT catalog_name, schema_name, sql_path
 FROM information_schema.schemata
 WHERE catalog_name IS NOT NULL or sql_path IS NOT NULL
@@ -77,9 +80,9 @@ GRANT SELECT ON db_datadict_1.* to 'testuser2'@'localhost';
 GRANT SELECT ON db_datadict_2.* to 'testuser2'@'localhost';
 SELECT * FROM information_schema.schemata
 WHERE schema_name LIKE 'db_datadict_%' ORDER BY schema_name;
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
-def	db_datadict_1	latin1	latin1_swedish_ci	NULL
-def	db_datadict_2	latin1	latin1_swedish_ci	NULL
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
+def	db_datadict_1	latin1	latin1_swedish_ci	NULL	
+def	db_datadict_2	latin1	latin1_swedish_ci	NULL	
 SHOW DATABASES LIKE 'db_datadict_%';
 Database (db_datadict_%)
 db_datadict_1
@@ -87,17 +90,17 @@ db_datadict_2
 connect  testuser1, localhost, testuser1, , db_datadict_1;
 SELECT * FROM information_schema.schemata
 WHERE schema_name LIKE 'db_datadict_%' ORDER BY schema_name;
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
-def	db_datadict_1	latin1	latin1_swedish_ci	NULL
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
+def	db_datadict_1	latin1	latin1_swedish_ci	NULL	
 SHOW DATABASES LIKE 'db_datadict_%';
 Database (db_datadict_%)
 db_datadict_1
 connect  testuser2, localhost, testuser2, , db_datadict_2;
 SELECT * FROM information_schema.schemata
 WHERE schema_name LIKE 'db_datadict_%' ORDER BY schema_name;
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
-def	db_datadict_1	latin1	latin1_swedish_ci	NULL
-def	db_datadict_2	latin1	latin1_swedish_ci	NULL
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
+def	db_datadict_1	latin1	latin1_swedish_ci	NULL	
+def	db_datadict_2	latin1	latin1_swedish_ci	NULL	
 SHOW DATABASES LIKE 'db_datadict_%';
 Database (db_datadict_%)
 db_datadict_1
@@ -105,7 +108,7 @@ db_datadict_2
 connect  testuser3, localhost, testuser3, , test;
 SELECT * FROM information_schema.schemata
 WHERE schema_name LIKE 'db_datadict_%' ORDER BY schema_name;
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
 SHOW DATABASES LIKE 'db_datadict_%';
 Database (db_datadict_%)
 connection default;
@@ -122,11 +125,11 @@ DROP DATABASE db_datadict_2;
 #################################################################################
 DROP DATABASE IF EXISTS db_datadict;
 SELECT * FROM information_schema.schemata WHERE schema_name = 'db_datadict';
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
 CREATE DATABASE db_datadict CHARACTER SET 'latin1' COLLATE 'latin1_swedish_ci';
 SELECT * FROM information_schema.schemata WHERE schema_name = 'db_datadict';
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
-def	db_datadict	latin1	latin1_swedish_ci	NULL
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
+def	db_datadict	latin1	latin1_swedish_ci	NULL	
 SELECT schema_name, default_character_set_name
 FROM information_schema.schemata WHERE schema_name = 'db_datadict';
 schema_name	default_character_set_name

mysql-test/suite/funcs_1/r/is_schemata_is_mysql_test.result

@@ -9,10 +9,10 @@ GRANT SELECT ON db_datadict.* TO 'testuser1'@'localhost';
 SELECT * FROM information_schema.schemata
 WHERE schema_name IN ('information_schema','mysql','test')
 ORDER BY schema_name;
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
-def	information_schema	utf8	utf8_general_ci	NULL
-def	mysql	latin1	latin1_swedish_ci	NULL
-def	test	latin1	latin1_swedish_ci	NULL
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
+def	information_schema	utf8	utf8_general_ci	NULL	
+def	mysql	latin1	latin1_swedish_ci	NULL	
+def	test	latin1	latin1_swedish_ci	NULL	
 SHOW DATABASES LIKE 'information_schema';
 Database (information_schema)
 information_schema
@@ -26,9 +26,9 @@ connect  testuser1, localhost, testuser1, , db_datadict;
 SELECT * FROM information_schema.schemata
 WHERE schema_name IN ('information_schema','mysql','test')
 ORDER BY schema_name;
-CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH
-def	information_schema	utf8	utf8_general_ci	NULL
-def	test	latin1	latin1_swedish_ci	NULL
+CATALOG_NAME	SCHEMA_NAME	DEFAULT_CHARACTER_SET_NAME	DEFAULT_COLLATION_NAME	SQL_PATH	SCHEMA_COMMENT
+def	information_schema	utf8	utf8_general_ci	NULL	
+def	test	latin1	latin1_swedish_ci	NULL	
 SHOW DATABASES LIKE 'information_schema';
 Database (information_schema)
 information_schema

sql/handler.h

@@ -1945,11 +1945,12 @@ enum enum_stats_auto_recalc { HA_STATS_AUTO_RECALC_DEFAULT= 0,
 
   It stores the "schema_specification" part of the CREATE/ALTER statements and
   is passed to mysql_create_db() and  mysql_alter_db().
-  Currently consists only of the schema default character set and collation.
+  Currently consists of the schema default character set, collation and schema_comment.
 */
 struct Schema_specification_st
 {
   CHARSET_INFO *default_table_charset;
+  LEX_CSTRING *schema_comment;
   void init()
   {
     bzero(this, sizeof(*this));

sql/share/errmsg-utf8.txt

@@ -7931,3 +7931,5 @@ ER_PERIOD_CONSTRAINT_DROP
         eng "Can't DROP CONSTRAINT `%s`. Use DROP PERIOD `%s` for this"
 ER_TOO_LONG_KEYPART 42000 S1009
         eng "Specified key part was too long; max key part length is %u bytes"
+ER_TOO_LONG_DATABASE_COMMENT
+  eng "Comment for database '%-.64s' is too long (max = %u)"

sql/sql_db.cc

@@ -26,6 +26,7 @@
 #include "lock.h"                        // lock_schema_name
 #include "sql_table.h"                   // build_table_filename,
                                          // filename_to_tablename
+                                         // validate_comment_length
 #include "sql_rename.h"                  // mysql_rename_tables
 #include "sql_acl.h"                     // SELECT_ACL, DB_ACLS,
                                          // acl_get, check_grant_db
@@ -77,6 +78,7 @@ typedef struct my_dbopt_st
   char *name;			/* Database name                  */
   uint name_length;		/* Database length name           */
   CHARSET_INFO *charset;	/* Database default character set */
+  LEX_STRING comment;           /* Database comment               */
 } my_dbopt_t;
 
 
@@ -235,7 +237,8 @@ void my_dbopt_cleanup(void)
     1 on error.
 */
 
-static my_bool get_dbopt(const char *dbname, Schema_specification_st *create)
+static my_bool get_dbopt(THD *thd, const char *dbname,
+                         Schema_specification_st *create)
 {
   my_dbopt_t *opt;
   uint length;
@@ -247,6 +250,11 @@ static my_bool get_dbopt(const char *dbname, Schema_specification_st *create)
   if ((opt= (my_dbopt_t*) my_hash_search(&dboptions, (uchar*) dbname, length)))
   {
     create->default_table_charset= opt->charset;
+    if (opt->comment.length)
+    {
+      create->schema_comment= thd->make_clex_string(const_cast<char*>(opt->comment.str),
+                                                    opt->comment.length);
+    }
     error= 0;
   }
   mysql_rwlock_unlock(&LOCK_dboptions);
@@ -274,15 +282,17 @@ static my_bool put_dbopt(const char *dbname, Schema_specification_st *create)
   DBUG_ENTER("put_dbopt");
 
   length= (uint) strlen(dbname);
-  
+
   mysql_rwlock_wrlock(&LOCK_dboptions);
   if (!(opt= (my_dbopt_t*) my_hash_search(&dboptions, (uchar*) dbname,
                                           length)))
   { 
     /* Options are not in the hash, insert them */
     char *tmp_name;
+    char *tmp_comment= NULL;
     if (!my_multi_malloc(MYF(MY_WME | MY_ZEROFILL),
                          &opt, (uint) sizeof(*opt), &tmp_name, (uint) length+1,
+                         &tmp_comment, (uint) DATABASE_COMMENT_MAXLEN+1,
                          NullS))
     {
       error= 1;
@@ -292,7 +302,7 @@ static my_bool put_dbopt(const char *dbname, Schema_specification_st *create)
     opt->name= tmp_name;
     strmov(opt->name, dbname);
     opt->name_length= length;
-    
+    opt->comment.str= tmp_comment;
     if (unlikely((error= my_hash_insert(&dboptions, (uchar*) opt))))
     {
       my_free(opt);
@@ -303,6 +313,12 @@ static my_bool put_dbopt(const char *dbname, Schema_specification_st *create)
   /* Update / write options in hash */
   opt->charset= create->default_table_charset;
 
+  if (create->schema_comment)
+  {
+    strmov(opt->comment.str, create->schema_comment->str);
+    opt->comment.length= create->schema_comment->length;
+  }
+
 end:
   mysql_rwlock_unlock(&LOCK_dboptions);
   DBUG_RETURN(error);
@@ -328,7 +344,7 @@ static void del_dbopt(const char *path)
   Create database options file:
 
   DESCRIPTION
-    Currently database default charset is only stored there.
+    Currently database default charset, default collation and comment are stored there.
 
   RETURN VALUES
   0	ok
@@ -339,9 +355,31 @@ static bool write_db_opt(THD *thd, const char *path,
                          Schema_specification_st *create)
 {
   File file;
-  char buf[256]; // Should be enough for one option
+  char buf[256+DATABASE_COMMENT_MAXLEN];
   bool error=1;
 
+  if (create->schema_comment)
+  {
+    if (validate_comment_length(thd, create->schema_comment,
+                                DATABASE_COMMENT_MAXLEN, ER_TOO_LONG_DATABASE_COMMENT,
+                                thd->lex->name.str))
+      return error;
+  }
+
+  /* Use existing values of schema_comment and charset for ALTER DATABASE queries */
+  Schema_specification_st tmp;
+  bzero((char*) &tmp,sizeof(tmp));
+  if (thd->lex->sql_command == SQLCOM_ALTER_DB)
+  {
+    load_db_opt(thd, path, &tmp);
+
+    if (!create->schema_comment)
+      create->schema_comment= tmp.schema_comment;
+
+    if (!create->default_table_charset)
+      create->default_table_charset= tmp.default_table_charset;
+  }
+
   if (!create->default_table_charset)
     create->default_table_charset= thd->variables.collation_server;
 
@@ -358,6 +396,11 @@ static bool write_db_opt(THD *thd, const char *path,
                               create->default_table_charset->name,
                               "\n", NullS) - buf);
 
+    if (create->schema_comment)
+      length= (ulong) (strxnmov(buf+length, sizeof(buf)-1-length,
+                                "comment=", create->schema_comment->str,
+                                "\n", NullS) - buf);
+
     /* Error is written by mysql_file_write */
     if (!mysql_file_write(file, (uchar*) buf, length, MYF(MY_NABP+MY_WME)))
       error=0;
@@ -385,7 +428,7 @@ static bool write_db_opt(THD *thd, const char *path,
 bool load_db_opt(THD *thd, const char *path, Schema_specification_st *create)
 {
   File file;
-  char buf[256];
+  char buf[256+DATABASE_COMMENT_MAXLEN];
   DBUG_ENTER("load_db_opt");
   bool error=1;
   size_t nbytes;
@@ -394,7 +437,7 @@ bool load_db_opt(THD *thd, const char *path, Schema_specification_st *create)
   create->default_table_charset= thd->variables.collation_server;
 
   /* Check if options for this database are already in the hash */
-  if (!get_dbopt(path, create))
+  if (!get_dbopt(thd, path, create))
     DBUG_RETURN(0);
 
   /* Otherwise, load options from the .opt file */
@@ -444,6 +487,8 @@ bool load_db_opt(THD *thd, const char *path, Schema_specification_st *create)
           create->default_table_charset= default_charset_info;
         }
       }
+      else if (!strncmp(buf, "comment", (pos-buf)))
+        create->schema_comment= thd->make_clex_string(pos+1, strlen(pos+1));
     }
   }
   /*
@@ -544,7 +589,7 @@ CHARSET_INFO *get_default_db_collation(THD *thd, const char *db_name)
   Create a database
 
   SYNOPSIS
-  mysql_create_db_iternal()
+  mysql_create_db_internal()
   thd		Thread handler
   db		Name of database to create
 		Function assumes that this is already validated.

sql/sql_show.cc

@@ -1470,7 +1470,7 @@ bool mysqld_show_create_db(THD *thd, LEX_CSTRING *dbname,
                            LEX_CSTRING *orig_dbname,
                            const DDL_options_st &options)
 {
-  char buff[2048];
+  char buff[2048+DATABASE_COMMENT_MAXLEN];
   String buffer(buff, sizeof(buff), system_charset_info);
 #ifndef NO_EMBEDDED_ACCESS_CHECKS
   Security_context *sctx= thd->security_ctx;
@@ -1506,6 +1506,7 @@ bool mysqld_show_create_db(THD *thd, LEX_CSTRING *dbname,
   {
     *dbname= INFORMATION_SCHEMA_NAME;
     create.default_table_charset= system_charset_info;
+    create.schema_comment= NULL;
   }
   else
   {
@@ -1545,6 +1546,13 @@ bool mysqld_show_create_db(THD *thd, LEX_CSTRING *dbname,
     }
     buffer.append(STRING_WITH_LEN(" */"));
   }
+
+  if (create.schema_comment)
+  {
+    buffer.append(STRING_WITH_LEN(" COMMENT "));
+    append_unescaped(&buffer, create.schema_comment->str,
+                     create.schema_comment->length);
+  }
   protocol->store(buffer.ptr(), buffer.length(), buffer.charset());
 
   if (protocol->write())
@@ -5306,14 +5314,16 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
 }
 
 
-bool store_schema_shemata(THD* thd, TABLE *table, LEX_CSTRING *db_name,
-                          CHARSET_INFO *cs)
+bool store_schema_schemata(THD* thd, TABLE *table, LEX_CSTRING *db_name,
+                           CHARSET_INFO *cs, LEX_CSTRING *schema_comment= NULL)
 {
   restore_record(table, s->default_values);
   table->field[0]->store(STRING_WITH_LEN("def"), system_charset_info);
   table->field[1]->store(db_name->str, db_name->length, system_charset_info);
   table->field[2]->store(cs->csname, strlen(cs->csname), system_charset_info);
   table->field[3]->store(cs->name, strlen(cs->name), system_charset_info);
+  if (schema_comment)
+    table->field[5]->store(schema_comment->str, schema_comment->length, system_charset_info);
   return schema_table_store_record(thd, table);
 }
 
@@ -5366,8 +5376,8 @@ int fill_schema_schemata(THD *thd, TABLE_LIST *tables, COND *cond)
     DBUG_ASSERT(db_name->length <= NAME_LEN);
     if (db_name == &INFORMATION_SCHEMA_NAME)
     {
-      if (store_schema_shemata(thd, table, db_name,
-                               system_charset_info))
+      if (store_schema_schemata(thd, table, db_name,
+                                system_charset_info))
         DBUG_RETURN(1);
       continue;
     }
@@ -5380,8 +5390,8 @@ int fill_schema_schemata(THD *thd, TABLE_LIST *tables, COND *cond)
 #endif
     {
       load_db_opt_by_name(thd, db_name->str, &create);
-      if (store_schema_shemata(thd, table, db_name,
-                               create.default_table_charset))
+      if (store_schema_schemata(thd, table, db_name,
+                                create.default_table_charset, create.schema_comment))
         DBUG_RETURN(1);
     }
   }
@@ -9044,6 +9054,7 @@ ST_FIELD_INFO schema_fields_info[]=
   {"DEFAULT_COLLATION_NAME", MY_CS_NAME_SIZE, MYSQL_TYPE_STRING, 0, 0, 0,
    SKIP_OPEN_TABLE},
   {"SQL_PATH", FN_REFLEN, MYSQL_TYPE_STRING, 0, 1, 0, SKIP_OPEN_TABLE},
+  {"SCHEMA_COMMENT", DATABASE_COMMENT_MAXLEN, MYSQL_TYPE_STRING, 0, 0, 0, SKIP_OPEN_TABLE},
   {0, 0, MYSQL_TYPE_STRING, 0, 0, 0, SKIP_OPEN_TABLE}
 };
 

sql/sql_yacc.yy

@@ -1687,6 +1687,7 @@ bool my_yyoverflow(short **a, YYSTYPE **b, size_t *yystacksize);
 */
 %left   PREC_BELOW_IDENTIFIER_OPT_SPECIAL_CASE
 %left   TRANSACTION_SYM TIMESTAMP PERIOD_SYM SYSTEM USER
+%left   COMMENT_SYM
 
 
 /*
@@ -2793,6 +2794,7 @@ create:
         | create_or_replace DATABASE opt_if_not_exists ident
           {
             Lex->create_info.default_table_charset= NULL;
+            Lex->create_info.schema_comment= NULL;
             Lex->create_info.used_fields= 0;
             if (Lex->main_select_push())
               MYSQL_YYABORT;
@@ -6043,6 +6045,11 @@ create_database_options:
 create_database_option:
           default_collation {}
         | default_charset {}
+        | COMMENT_SYM opt_equal TEXT_STRING_sys
+          {
+            Lex->create_info.schema_comment= thd->make_clex_string($3);
+            Lex->create_info.used_fields|= HA_CREATE_USED_COMMENT;
+          }
         ;
 
 opt_if_not_exists_table_element:
@@ -7764,6 +7771,7 @@ alter:
         | ALTER DATABASE ident_or_empty
           {
             Lex->create_info.default_table_charset= NULL;
+            Lex->create_info.schema_comment= NULL;
             Lex->create_info.used_fields= 0;
             if (Lex->main_select_push())
               MYSQL_YYABORT;
@@ -7778,6 +7786,22 @@ alter:
               MYSQL_YYABORT;
             Lex->pop_select(); //main select
           }
+        | ALTER DATABASE COMMENT_SYM opt_equal TEXT_STRING_sys
+          {
+            Lex->create_info.default_table_charset= NULL;
+            Lex->create_info.used_fields= 0;
+            Lex->create_info.schema_comment= thd->make_clex_string($5);
+            Lex->create_info.used_fields|= HA_CREATE_USED_COMMENT;
+          }
+          opt_create_database_options
+          {
+            LEX *lex=Lex;
+            lex->sql_command=SQLCOM_ALTER_DB;
+            lex->name= Lex_ident_sys();
+            if (lex->name.str == NULL &&
+                unlikely(lex->copy_db_to(&lex->name)))
+              MYSQL_YYABORT;
+          }
         | ALTER DATABASE ident UPGRADE_SYM DATA_SYM DIRECTORY_SYM NAME_SYM
           {
             LEX *lex= Lex;
@@ -8022,7 +8046,7 @@ opt_ev_sql_stmt:
         ;
 
 ident_or_empty:
-          /* empty */ { $$= Lex_ident_sys(); }
+          /* empty */ %prec PREC_BELOW_IDENTIFIER_OPT_SPECIAL_CASE { $$= Lex_ident_sys(); }
         | ident
         ;