build_frm_image(): don't try to guess the "real table name" from the

field list, it doesn't work if ALTER TABLE has replaced all fields.
Instead, pass the correct original table name down from the caller.

mysql-test/r/comment_column.result

@@ -408,4 +408,7 @@ Warning	1688	Comment for index 'i1' is too long (max = 1024)
 CREATE INDEX i2 ON t1_toupg(c2) COMMENT '01234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234';
 Warnings:
 Warning	1688	Comment for index 'i2' is too long (max = 1024)
+ALTER TABLE t1_toupg drop column c1, drop column c2, drop column c3, add column c4 int, COMMENT='012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012301234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234';
+Warnings:
+Warning	1628	Comment for table 't1_toupg' is too long (max = 2048)
 drop table t1_toupg;

mysql-test/t/comment_column.test

@@ -125,6 +125,8 @@ ALTER TABLE t1_toupg ADD c3 TIMESTAMP COMMENT 'abcdefghijabcdefghijabcdefghijabc
 ALTER TABLE t1_toupg ADD INDEX i1(c1) COMMENT '01234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234'; 
 # Add index with comment using CREATE INDEX 
 CREATE INDEX i2 ON t1_toupg(c2) COMMENT '01234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234'; 
+# Alter the existing table, replace all columns, change comment 
+ALTER TABLE t1_toupg drop column c1, drop column c2, drop column c3, add column c4 int, COMMENT='012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012301234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234'; 
 drop table t1_toupg;
 
 

sql/sql_table.cc

@@ -4559,6 +4559,9 @@ handler *mysql_create_frm_image(THD *thd,
   Create a table
 
   @param thd                 Thread object
+  @param orig_db             Database for error messages
+  @param orig_table_name     Table name for error messages
+                             (it's different from table_name for ALTER TABLE)
   @param db                  Database
   @param table_name          Table name
   @param path                Path to table (i.e. to its .FRM file without
@@ -4587,6 +4590,7 @@ handler *mysql_create_frm_image(THD *thd,
 
 static
 int create_table_impl(THD *thd,
+                       const char *orig_db, const char *orig_table_name,
                        const char *db, const char *table_name,
                        const char *path,
                        HA_CREATE_INFO *create_info,
@@ -4767,8 +4771,9 @@ int create_table_impl(THD *thd,
   }
   else
   {
-    file= mysql_create_frm_image(thd, db, table_name, create_info, alter_info,
-                                 create_table_mode, key_info, key_count, frm);
+    file= mysql_create_frm_image(thd, orig_db, orig_table_name, create_info,
+                                 alter_info, create_table_mode, key_info,
+                                 key_count, frm);
     if (!file)
       goto err;
     if (rea_create_table(thd, frm, path, db, table_name, create_info,
@@ -4884,9 +4889,9 @@ int mysql_create_table_no_lock(THD *thd,
     }
   }
 
-  res= create_table_impl(thd, db, table_name, path, create_info,
-                         alter_info, create_table_mode, is_trans,
-                         &not_used_1, &not_used_2, &frm);
+  res= create_table_impl(thd, db, table_name, db, table_name, path,
+                         create_info, alter_info, create_table_mode,
+                         is_trans, &not_used_1, &not_used_2, &frm);
   my_free(const_cast<uchar*>(frm.str));
   return res;
 }
@@ -8514,7 +8519,9 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
 
   tmp_disable_binlog(thd);
   create_info->options|=HA_CREATE_TMP_ALTER;
-  error= create_table_impl(thd, alter_ctx.new_db, alter_ctx.tmp_name,
+  error= create_table_impl(thd,
+                           alter_ctx.db, alter_ctx.table_name,
+                           alter_ctx.new_db, alter_ctx.tmp_name,
                            alter_ctx.get_tmp_path(),
                            create_info, alter_info,
                            C_ALTER_TABLE_FRM_ONLY, NULL,

sql/unireg.cc

@@ -173,24 +173,15 @@ LEX_CUSTRING build_frm_image(THD *thd, const char *table,
 
   if (tmp_len < create_info->comment.length)
   {
-    char *real_table_name= (char*) table;
-    List_iterator<Create_field> it(create_fields);
-    Create_field *field;
-    while ((field=it++))
-    {
-      if (field->field && field->field->table &&
-         (real_table_name= field->field->table->s->table_name.str))
-        break;
-    }
     if (thd->is_strict_mode())
     {
       my_error(ER_TOO_LONG_TABLE_COMMENT, MYF(0),
-               real_table_name, TABLE_COMMENT_MAXLEN);
+               table, TABLE_COMMENT_MAXLEN);
       DBUG_RETURN(frm);
     }
     char warn_buff[MYSQL_ERRMSG_SIZE];
     my_snprintf(warn_buff, sizeof(warn_buff), ER(ER_TOO_LONG_TABLE_COMMENT),
-                real_table_name, TABLE_COMMENT_MAXLEN);
+                table, TABLE_COMMENT_MAXLEN);
     push_warning(current_thd, Sql_condition::WARN_LEVEL_WARN,
                  ER_TOO_LONG_TABLE_COMMENT, warn_buff);
     create_info->comment.length= tmp_len;