diff --git a/src/allographer/schema_builder/models/column.nim b/src/allographer/schema_builder/models/column.nim
index ff99f923..fce185cc 100644
--- a/src/allographer/schema_builder/models/column.nim
+++ b/src/allographer/schema_builder/models/column.nim
@@ -20,6 +20,7 @@ type Column* = ref object
   defaultDatetime*: DefaultDateTime
   foreignOnDelete*: ForeignOnDelete
   commentContent*:string
+  isCommentNull*:bool
   info*: JsonNode
   checksum*:string
   # alter table
@@ -51,6 +52,7 @@ proc toSchema*(self:Column):JsonNode =
     "defaultJson": self.defaultJson,
     "foreignOnDelete": self.foreignOnDelete,
     "comment": self.commentContent,
+    "isCommentNull": self.isCommentNull,
     "info": self.info,
     "previousName":self.previousName,
     "migrationType":self.migrationType,
@@ -389,6 +391,10 @@ proc comment*(c: Column, value:string): Column =
   c.commentContent = value
   return c
 
+proc comment*(c: Column, arg:type nil): Column =
+  c.isCommentNull = true
+  return c
+
 
 # =============================================================================
 # alter table
diff --git a/src/allographer/schema_builder/queries/postgres/change_column.nim b/src/allographer/schema_builder/queries/postgres/change_column.nim
index 1859e797..96dd2425 100644
--- a/src/allographer/schema_builder/queries/postgres/change_column.nim
+++ b/src/allographer/schema_builder/queries/postgres/change_column.nim
@@ -6,17 +6,13 @@ else:
 import std/json
 import ../../models/table
 import ../../models/column
-import ../../enums
 import ./schema_utils
 import ./postgres_query_type
 import ./sub/change_column_query
 
 
 proc changeColumn*(self:PostgresSchema, isReset:bool) =
-  var queries = changeColumnString(self.table, self.column)
-  
-  if self.column.isIndex and self.column.typ != rdbIncrements:
-    queries.add(changeIndexString(self.table, self.column))
+  let queries = changeColumnString(self.table, self.column)
 
   let schema = $self.column.toSchema()
   let checksum = $schema.secureHash()
diff --git a/src/allographer/schema_builder/queries/postgres/sub/add_column_query.nim b/src/allographer/schema_builder/queries/postgres/sub/add_column_query.nim
index 84a0cb24..37740417 100644
--- a/src/allographer/schema_builder/queries/postgres/sub/add_column_query.nim
+++ b/src/allographer/schema_builder/queries/postgres/sub/add_column_query.nim
@@ -421,6 +421,14 @@ proc addIndexColumn(column:Column, table:Table):string =
   return &"CREATE INDEX IF NOT EXISTS \"{table.name}_{column.name}_index\" ON \"{table.name}\"(\"{column.name}\")"
 
 
+proc addCommentColumn(column:Column, table:Table):string =
+  return &"COMMENT ON COLUMN \"{table.name}\".\"{column.name}\" IS '{column.commentContent}'"
+
+
+proc addNullCommentColumn(column:Column, table:Table):string =
+  return &"COMMENT ON COLUMN \"{table.name}\".\"{column.name}\" IS NULL"
+
+
 proc addColumnString*(table:Table, column:Column):seq[string] =
   var queries:seq[string]
   case column.typ:
@@ -492,4 +500,9 @@ proc addColumnString*(table:Table, column:Column):seq[string] =
   if column.isUpdatedAt:
     queries.add(column.addUpdatedAtColumn(table))
 
+  if column.commentContent.len > 0:
+    queries.add(column.addCommentColumn(table))
+  elif column.isCommentNull:
+    queries.add(column.addNullCommentColumn(table))
+
   return queries
diff --git a/src/allographer/schema_builder/queries/postgres/sub/change_column_query.nim b/src/allographer/schema_builder/queries/postgres/sub/change_column_query.nim
index bb88730d..589b5875 100644
--- a/src/allographer/schema_builder/queries/postgres/sub/change_column_query.nim
+++ b/src/allographer/schema_builder/queries/postgres/sub/change_column_query.nim
@@ -347,68 +347,83 @@ proc indexColumn(column:Column, table:Table):string =
   return &"CREATE INDEX IF NOT EXISTS \"{table.name}_{column.name}_index\" ON \"{table.name}\"(\"{column.name}\")"
 
 
+proc addCommentColumn(column:Column, table:Table):string =
+  return &"COMMENT ON COLUMN \"{table.name}\".\"{column.name}\" IS '{column.commentContent}'"
+
+
+proc addNullCommentColumn(column:Column, table:Table):string =
+  return &"COMMENT ON COLUMN \"{table.name}\".\"{column.name}\" IS NULL"
+
+
 proc changeColumnString*(table:Table, column:Column):seq[string] =
+  var queries:seq[string]
   case column.typ:
     # int
   of rdbIncrements:
-    notAllowedType("increments")
+    queries = column.changeIntColumn(table)
   of rdbInteger:
-    return column.changeIntColumn(table)
+    queries = column.changeIntColumn(table)
   of rdbSmallInteger:
-    return column.changeSmallIntColumn(table)
+    queries = column.changeSmallIntColumn(table)
   of rdbMediumInteger:
-    return column.changeMediumIntColumn(table)
+    queries = column.changeMediumIntColumn(table)
   of rdbBigInteger:
-    return column.changeBigIntColumn(table)
+    queries = column.changeBigIntColumn(table)
     # float
   of rdbDecimal:
-    return column.changeDecimalColumn(table)
+    queries = column.changeDecimalColumn(table)
   of rdbDouble:
-    return column.changeDecimalColumn(table)
+    queries = column.changeDecimalColumn(table)
   of rdbFloat:
-    return column.changeFloatColumn(table)
+    queries = column.changeFloatColumn(table)
     # char
   of rdbUuid:
-    return column.changeStringColumn(table)
+    queries = column.changeStringColumn(table)
   of rdbChar:
-    return column.changeCharColumn(table)
+    queries = column.changeCharColumn(table)
   of rdbString:
-    return column.changeStringColumn(table)
+    queries = column.changeStringColumn(table)
     # text
   of rdbText:
-    return column.changeTextColumn(table)
+    queries = column.changeTextColumn(table)
   of rdbMediumText:
-    return column.changeTextColumn(table)
+    queries = column.changeTextColumn(table)
   of rdbLongText:
-    return column.changeTextColumn(table)
+    queries = column.changeTextColumn(table)
     # date
   of rdbDate:
-    return column.changeDateColumn(table)
+    queries = column.changeDateColumn(table)
   of rdbDatetime:
-    return column.changeDatetimeColumn(table)
+    queries = column.changeDatetimeColumn(table)
   of rdbTime:
-    return column.changeTimeColumn(table)
+    queries = column.changeTimeColumn(table)
   of rdbTimestamp:
-    return column.changeTimestampColumn(table)
+    queries = column.changeTimestampColumn(table)
   of rdbTimestamps:
     notAllowedType("timestamps")
   of rdbSoftDelete:
     notAllowedType("softDelete")
     # others
   of rdbBinary:
-    return column.changeBlobColumn(table)
+    queries = column.changeBlobColumn(table)
   of rdbBoolean:
-    return column.changeBoolColumn(table)
+    queries = column.changeBoolColumn(table)
   of rdbEnumField:
-    return column.changeEnumColumn(table)
+    queries = column.changeEnumColumn(table)
   of rdbJson:
-    return column.changeJsonColumn(table)
+    queries = column.changeJsonColumn(table)
   # foreign
   of rdbForeign:
     notAllowedType("foreign")
   of rdbStrForeign:
     notAllowedType("strForeign")
 
+  if column.isIndex and column.typ != rdbIncrements:
+    queries.add(indexColumn(column, table))
+
+  if column.commentContent.len > 0:
+    queries.add(column.addCommentColumn(table))
+  elif column.isCommentNull:
+    queries.add(column.addNullCommentColumn(table))
 
-proc changeIndexString*(table:Table, column:Column):string =
-  return column.indexColumn(table)
+  return queries
diff --git a/src/allographer/schema_builder/usecases/postgres/create_schema.nim b/src/allographer/schema_builder/usecases/postgres/create_schema.nim
index de87355d..541ef696 100644
--- a/src/allographer/schema_builder/usecases/postgres/create_schema.nim
+++ b/src/allographer/schema_builder/usecases/postgres/create_schema.nim
@@ -77,9 +77,21 @@ proc generateSchemaCode(tablesInfo: Table[string, seq[tuple[name: string, typ: s
 
 
 proc createSchema*(rdb: PostgresConnections, schemaPath="") {.async.} =
-  ## create schema.nim
-  let tablesInfo = rdb.getTableInfo().await
-  let schemaCode = generateSchemaCode(tablesInfo)
-  
-  writeFile(schemaPath / "schema.nim", schemaCode)
-  echo "schema.nim generated successfully"
+  ## if schemaPath is not specified, the schema will be generated in the current directory
+  ## 
+  ## Default schema file name is `getCurrentDir() / "schema.nim"`
+  try:
+    let tablesInfo = rdb.getTableInfo().await
+    let schemaCode = generateSchemaCode(tablesInfo)
+
+    let schemaFilePath =
+      if schemaPath == "":
+        getCurrentDir() / "schema.nim"
+      else:
+        schemaPath
+    
+    writeFile(schemaFilePath, schemaCode)
+    echo "schema generated successfully in ", schemaFilePath
+  except Exception as e:
+    echo "Error generating schema: ", e.msg
+    raise
diff --git a/src/allographer/schema_builder/usecases/sqlite/create_schema.nim b/src/allographer/schema_builder/usecases/sqlite/create_schema.nim
index 813d5de1..3d5abc73 100644
--- a/src/allographer/schema_builder/usecases/sqlite/create_schema.nim
+++ b/src/allographer/schema_builder/usecases/sqlite/create_schema.nim
@@ -74,14 +74,21 @@ proc generateSchemaCode(tablesInfo: Table[string, seq[tuple[name: string, typ: s
   return code
 
 proc createSchema*(rdb: SqliteConnections, schemaPath="") {.async.} =
-  ## create schema.nim
+  ## if schemaPath is not specified, the schema will be generated in the current directory
+  ## 
+  ## Default schema file name is `getCurrentDir() / "schema.nim"`
   try:
     let tablesInfo = await rdb.getTableInfo()
     let schemaCode = generateSchemaCode(tablesInfo)
+
+    let schemaFilePath =
+      if schemaPath == "":
+        getCurrentDir() / "schema.nim"
+      else:
+        schemaPath
     
-    writeFile(schemaPath / "schema.nim", schemaCode)
-    echo "schema.nim generated successfully"
-    
+    writeFile(schemaFilePath, schemaCode)
+    echo "schema generated successfully in ", schemaFilePath
   except Exception as e:
     echo "Error generating schema: ", e.msg
     raise
diff --git a/tests/clear_tables.nim b/tests/clear_tables.nim
index b6ab6efb..a5d669a0 100644
--- a/tests/clear_tables.nim
+++ b/tests/clear_tables.nim
@@ -6,51 +6,66 @@ import ../src/allographer/query_builder
 
 
 proc clearTables*(rdb:PostgresConnections) {.async.} =
-  let tables = rdb.table("_allographer_migrations").orderBy("id", Desc) .get().await
-  for table in tables:
-    let tableName = table["name"].getStr()
-    if not tableName.startsWith("_"):
-      rdb.raw(&"DROP TABLE IF EXISTS \"{tableName}\"").exec().await
+  try:
+    let tables = rdb.table("_allographer_migrations").orderBy("id", Desc) .get().await
+    for table in tables:
+      let tableName = table["name"].getStr()
+      if not tableName.startsWith("_"):
+        rdb.raw(&"DROP TABLE IF EXISTS \"{tableName}\"").exec().await
 
-  rdb.raw("DROP TABLE IF EXISTS \"_allographer_migrations\"").exec().await
+    rdb.raw("DROP TABLE IF EXISTS \"_allographer_migrations\"").exec().await
+  except:
+    echo "error: ", getCurrentExceptionMsg()
 
 
 proc clearTables*(rdb:MariaDBConnections) {.async.} =
-  let tables = rdb.table("_allographer_migrations").orderBy("id", Desc) .get().await
-  for table in tables:
-    let tableName = table["name"].getStr()
-    if not tableName.startsWith("_"):
-      rdb.raw(&"DROP TABLE IF EXISTS `{tableName}`").exec().await
-  
-  rdb.raw("DROP TABLE IF EXISTS `_allographer_migrations`").exec().await
+  try:
+    let tables = rdb.table("_allographer_migrations").orderBy("id", Desc) .get().await
+    for table in tables:
+      let tableName = table["name"].getStr()
+      if not tableName.startsWith("_"):
+        rdb.raw(&"DROP TABLE IF EXISTS `{tableName}`").exec().await
+    
+    rdb.raw("DROP TABLE IF EXISTS `_allographer_migrations`").exec().await
+  except:
+    echo "error: ", getCurrentExceptionMsg()
 
 
 proc clearTables*(rdb:MySQLConnections) {.async.} =
-  let tables = rdb.table("_allographer_migrations").orderBy("id", Desc) .get().await
-  for table in tables:
-    let tableName = table["name"].getStr()
-    if not tableName.startsWith("_"):
-      rdb.raw(&"DROP TABLE IF EXISTS `{tableName}`").exec().await
-  
-  rdb.raw("DROP TABLE IF EXISTS `_allographer_migrations`").exec().await
+  try:
+    let tables = rdb.table("_allographer_migrations").orderBy("id", Desc) .get().await
+    for table in tables:
+      let tableName = table["name"].getStr()
+      if not tableName.startsWith("_"):
+        rdb.raw(&"DROP TABLE IF EXISTS `{tableName}`").exec().await
+    
+    rdb.raw("DROP TABLE IF EXISTS `_allographer_migrations`").exec().await
+  except:
+    echo "error: ", getCurrentExceptionMsg()
 
 
 proc clearTables*(rdb:SqliteConnections) {.async.} =
-  let tables = rdb.table("_allographer_migrations").orderBy("id", Desc) .get().await
-  for table in tables:
-    let tableName = table["name"].getStr()
-    if not tableName.startsWith("_"):
-      rdb.raw(&"DROP TABLE IF EXISTS \"{tableName}\"").exec().await
+  try:
+    let tables = rdb.table("_allographer_migrations").orderBy("id", Desc) .get().await
+    for table in tables:
+      let tableName = table["name"].getStr()
+      if not tableName.startsWith("_"):
+        rdb.raw(&"DROP TABLE IF EXISTS \"{tableName}\"").exec().await
 
-  rdb.raw("DROP TABLE IF EXISTS \"_allographer_migrations\"").exec().await
+    rdb.raw("DROP TABLE IF EXISTS \"_allographer_migrations\"").exec().await
+  except:
+    echo "error: ", getCurrentExceptionMsg()
 
 
 proc clearTables*(rdb:SurrealConnections) {.async.} =
-  let dbInfo = rdb.raw("INFO FOR DB").info().await
-  let tables = dbInfo[0]["result"]["tb"]
-  for (table, _) in tables.pairs:
-    if not table.startsWith("_"):
-      rdb.raw(&"REMOVE TABLE {table}").exec().await
+  try:
+    let dbInfo = rdb.raw("INFO FOR DB").info().await
+    let tables = dbInfo[0]["result"]["tb"]
+    for (table, _) in tables.pairs:
+      if not table.startsWith("_"):
+        rdb.raw(&"REMOVE TABLE {table}").exec().await
   
-  rdb.raw(&"REMOVE TABLE _allographer_migrations").exec().await
-  rdb.raw(&"REMOVE TABLE _autoincrement_sequences").exec().await
+    rdb.raw(&"REMOVE TABLE _allographer_migrations").exec().await
+    rdb.raw(&"REMOVE TABLE _autoincrement_sequences").exec().await
+  except:
+    echo "error: ", getCurrentExceptionMsg()
diff --git a/tests/postgres/test_create_schema.nim b/tests/postgres/test_create_schema.nim
index bb68e51c..8928917e 100644
--- a/tests/postgres/test_create_schema.nim
+++ b/tests/postgres/test_create_schema.nim
@@ -2,6 +2,8 @@ discard """
   cmd: "nim c -d:reset $file"
 """
 
+# nim c -d:reset -r tests/postgres/test_create_schema.nim
+
 import std/unittest
 import std/asyncdispatch
 import std/os
@@ -61,7 +63,7 @@ suite "Schema output after migration":
 
   test "should generate schema.nim file":
     # スキーマ生成
-    rdb.createSchema().waitFor()
+    rdb.createSchema(schemaFilePath).waitFor()
     
     # schema.nim ファイルの存在確認
     check fileExists(schemaFilePath)
diff --git a/tests/postgres/test_schema.nim b/tests/postgres/test_schema.nim
index 69ade141..5b25b399 100644
--- a/tests/postgres/test_schema.nim
+++ b/tests/postgres/test_schema.nim
@@ -15,6 +15,7 @@ import ../clear_tables
 
 
 let rdb = postgres
+clearTables(rdb).waitFor()
 
 suite("PostgreSQL create table"):
   test("create table"):
@@ -298,7 +299,7 @@ suite($rdb & " primary"):
 
 
 suite("Comment"):
-  test("column comment"):
+  test("create table with column comment"):
     rdb.create(
       table("Comment", [
         Column.integer("index1").comment("index1 comment"),
@@ -306,5 +307,26 @@ suite("Comment"):
       ])
     )
 
+  test("alter table change column comment"):
+    rdb.alter(
+      table("Comment", [
+        Column.integer("index1").comment("changed index1 comment").change()
+      ])
+    )
+
+  test("alter table add column comment"):
+    rdb.alter(
+      table("Comment", [
+        Column.string("string2").comment("string2 comment").add()
+      ])
+    )
+
+  test("alter table add null comment"):
+    rdb.alter(
+      table("Comment", [
+        Column.string("string").comment(nil).change()
+      ])
+    )
+
 
 clearTables(rdb).waitFor()
diff --git a/tests/sqlite/test_create_schema.nim b/tests/sqlite/test_create_schema.nim
index 6fc0738d..d6b2ff7f 100644
--- a/tests/sqlite/test_create_schema.nim
+++ b/tests/sqlite/test_create_schema.nim
@@ -2,6 +2,8 @@ discard """
   cmd: "nim c -d:reset $file"
 """
 
+# nim c -d:reset -r tests/sqlite/test_create_schema.nim
+
 import std/unittest
 import std/asyncdispatch
 import std/os
@@ -61,7 +63,7 @@ suite "Schema output after migration":
 
   test "should generate schema.nim file":
     # スキーマ生成
-    rdb.createSchema().waitFor()
+    rdb.createSchema(schemaFilePath).waitFor()
     
     # schema.nim ファイルの存在確認
     check fileExists(schemaFilePath)