diff --git a/docs-2.0/3.ngql-guide/10.tag-statements/1.create-tag.md b/docs-2.0/3.ngql-guide/10.tag-statements/1.create-tag.md
index 70f5c553b98..3b0cfe7d1cd 100644
--- a/docs-2.0/3.ngql-guide/10.tag-statements/1.create-tag.md
+++ b/docs-2.0/3.ngql-guide/10.tag-statements/1.create-tag.md
@@ -34,7 +34,7 @@ CREATE TAG [IF NOT EXISTS] <tag_name>
 |`<tag_name>`|1. The tag name must be **unique** in a graph space.<br> 2. Once the tag name is set, it can not be altered.<br> 3. The name of the tag starts with a letter, supports 1 to 4 bytes UTF-8 encoded characters, such as English letters (case-sensitive), digits, and Chinese characters, but does not support special characters except underscores. To use special characters (the period character (.) is excluded) or reserved keywords as identifiers, quote them with backticks. For more information, see [Keywords and reserved words](../../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md).|
 |`<prop_name>`|The name of the property. It must be unique for each tag. The rules for permitted property names are the same as those for tag names.|
 |`<data_type>`|Shows the data type of each property. For a full description of the property data types, see [Data types](../3.data-types/1.numeric.md) and [Boolean](../3.data-types/2.boolean.md).|
-|`NULL \| NOT NULL`|Specifies if the property supports `NULL | NOT NULL`. The default value is `NULL`.|
+|`NULL \| NOT NULL`|Specifies if the property supports `NULL | NOT NULL`. The default value is `NULL`. `DEFAULT` must be specified if `NOT NULL` is set.|
 |`DEFAULT`|Specifies a default value for a property. The default value can be a literal value or an expression supported by NebulaGraph. If no value is specified, the default value is used when inserting a new vertex.|
 |`COMMENT`|The remarks of a certain property or the tag itself. The maximum length is 256 bytes. By default, there will be no comments on a tag.|
 |`TTL_DURATION`|Specifies the life cycle for the property. The property that exceeds the specified TTL expires. The expiration threshold is the `TTL_COL` value plus the `TTL_DURATION`. The default value of `TTL_DURATION` is `0`. It means the data never expires.|
diff --git a/docs-2.0/3.ngql-guide/10.tag-statements/3.alter-tag.md b/docs-2.0/3.ngql-guide/10.tag-statements/3.alter-tag.md
index 7a1e62f186c..5ed938a18b9 100644
--- a/docs-2.0/3.ngql-guide/10.tag-statements/3.alter-tag.md
+++ b/docs-2.0/3.ngql-guide/10.tag-statements/3.alter-tag.md
@@ -29,6 +29,8 @@ ttl_definition:
 
 - Multiple `ADD`, `DROP`, and `CHANGE` clauses are permitted in a single `ALTER TAG` statement, separated by commas.
 
+- When a property value is set to `NOT NULL` using `ADD` or `CHANGE`, a default value must be specified for the property, that is, the value of `DEFAULT` must be specified.
+
 ## Examples
 
 ```ngql
diff --git a/docs-2.0/3.ngql-guide/11.edge-type-statements/1.create-edge.md b/docs-2.0/3.ngql-guide/11.edge-type-statements/1.create-edge.md
index 4e53f57593a..d07435ef79a 100644
--- a/docs-2.0/3.ngql-guide/11.edge-type-statements/1.create-edge.md
+++ b/docs-2.0/3.ngql-guide/11.edge-type-statements/1.create-edge.md
@@ -34,7 +34,7 @@ CREATE EDGE [IF NOT EXISTS] <edge_type_name>
 |`<edge_type_name>`|The edge type name must be **unique** in a graph space. Once the edge type name is set, it can not be altered. The name of the edge type starts with a letter, supports 1 to 4 bytes UTF-8 encoded characters, such as English letters (case-sensitive), digits, and Chinese characters, but does not support special characters except underscores. To use special characters or reserved keywords as identifiers, quote them with backticks. For more information, see [Keywords and reserved words](../../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md).|
 |`<prop_name>`|The name of the property. It must be unique for each edge type. The rules for permitted property names are the same as those for edge type names.|
 |`<data_type>`|Shows the data type of each property. For a full description of the property data types, see [Data types](../3.data-types/1.numeric.md) and [Boolean](../3.data-types/2.boolean.md).|
-|`NULL \| NOT NULL`|Specifies if the property supports `NULL | NOT NULL`. The default value is `NULL`.|
+|`NULL \| NOT NULL`|Specifies if the property supports `NULL | NOT NULL`. The default value is `NULL`. `DEFAULT` must be specified if `NOT NULL` is set.|
 |`DEFAULT`|Specifies a default value for a property. The default value can be a literal value or an expression supported by NebulaGraph. If no value is specified, the default value is used when inserting a new edge.|
 |`COMMENT`|The remarks of a certain property or the edge type itself. The maximum length is 256 bytes. By default, there will be no comments on an edge type.|
 |`TTL_DURATION`|Specifies the life cycle for the property. The property that exceeds the specified TTL expires. The expiration threshold is the `TTL_COL` value plus the `TTL_DURATION`. The default value of `TTL_DURATION` is `0`. It means the data never expires.|
diff --git a/docs-2.0/3.ngql-guide/11.edge-type-statements/3.alter-edge.md b/docs-2.0/3.ngql-guide/11.edge-type-statements/3.alter-edge.md
index 505eb07ccc3..aae7ec6955b 100644
--- a/docs-2.0/3.ngql-guide/11.edge-type-statements/3.alter-edge.md
+++ b/docs-2.0/3.ngql-guide/11.edge-type-statements/3.alter-edge.md
@@ -29,6 +29,8 @@ ttl_definition:
 
 - Multiple `ADD`, `DROP`, and `CHANGE` clauses are permitted in a single `ALTER EDGE` statement, separated by commas.
 
+- When a property value is set to `NOT NULL` using `ADD` or `CHANGE`, a default value must be specified for the property, that is, the value of `DEFAULT` must be specified.
+
 ## Example
 
 ```ngql