{"id":804,"date":"2025-01-11T00:16:36","date_gmt":"2025-01-10T16:16:36","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=804"},"modified":"2025-01-11T00:16:36","modified_gmt":"2025-01-10T16:16:36","slug":"%e5%a6%82%e4%bd%95%e5%9c%a8-c-%e4%b8%ad%e5%a4%84%e7%90%86-null-%e5%80%bc%e5%b9%b6%e5%b0%86%e5%85%b6%e6%ad%a3%e7%a1%ae%e5%9c%b0%e4%bc%a0%e9%80%92%e7%bb%99-sqlparameter","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/01\/11\/%e5%a6%82%e4%bd%95%e5%9c%a8-c-%e4%b8%ad%e5%a4%84%e7%90%86-null-%e5%80%bc%e5%b9%b6%e5%b0%86%e5%85%b6%e6%ad%a3%e7%a1%ae%e5%9c%b0%e4%bc%a0%e9%80%92%e7%bb%99-sqlparameter\/","title":{"rendered":"\u5982\u4f55\u5728 C# \u4e2d\u5904\u7406\u00a0NULL\u00a0\u503c\u5e76\u5c06\u5176\u6b63\u786e\u5730\u4f20\u9012\u7ed9\u00a0SqlParameter"},"content":{"rendered":"\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\u5728 C# \u4e2d\uff0c\u5c06 <code>NULL<\/code> \u503c\u6b63\u786e\u5730\u5206\u914d\u7ed9 <code>SqlParameter<\/code> \u65f6\uff0c\u786e\u4fdd\u4f20\u9012\u7684\u53c2\u6570\u80fd\u591f\u8bc6\u522b <code>NULL<\/code> \u503c\u975e\u5e38\u91cd\u8981\u3002C# \u7684 <code>null<\/code> \u548c SQL Server \u4e2d\u7684 <code>NULL<\/code> \u662f\u4e0d\u540c\u7684\uff0c\u6b63\u786e\u5730\u6620\u5c04\u5b83\u4eec\u9700\u8981\u4e00\u4e9b\u989d\u5916\u7684\u5904\u7406\u3002<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">\u4ee5\u4e0b\u662f\u51e0\u79cd\u5e38\u89c1\u7684\u5904\u7406\u65b9\u6cd5\uff1a<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">1. \u4f7f\u7528 <code>DBNull.Value<\/code><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\"><code>DBNull.Value<\/code> \u662f\u8868\u793a\u6570\u636e\u5e93\u4e2d\u7684 <code>NULL<\/code> \u503c\u7684\u7279\u6b8a\u5bf9\u8c61\u3002\u5f53\u4f60\u5c06 C# \u7684 <code>null<\/code> \u503c\u4f20\u9012\u7ed9 SQL \u67e5\u8be2\u65f6\uff0c\u5e94\u8be5\u4f7f\u7528 <code>DBNull.Value<\/code> \u6765\u8868\u793a\u6570\u636e\u5e93\u4e2d\u7684 <code>NULL<\/code> \u503c\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u793a\u4f8b\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>using System;\nusing System.Data;\nusing System.Data.SqlClient;\n\npublic class Program\n{\n    public static void Main()\n    {\n        \/\/ \u5047\u8bbe\u4f60\u6709\u4e00\u4e2a\u6570\u636e\u5e93\u8fde\u63a5\u548c\u547d\u4ee4\n        string connectionString = \"your_connection_string\";\n        using (SqlConnection conn = new SqlConnection(connectionString))\n        {\n            conn.Open();\n\n            string query = \"INSERT INTO Employees (Name, Age) VALUES (@Name, @Age)\";\n            using (SqlCommand cmd = new SqlCommand(query, conn))\n            {\n                \/\/ \u521b\u5efa SqlParameter\n                SqlParameter nameParam = new SqlParameter(\"@Name\", SqlDbType.NVarChar);\n                SqlParameter ageParam = new SqlParameter(\"@Age\", SqlDbType.Int);\n\n                \/\/ \u5982\u679c Age \u662f null\uff0c\u5219\u8bbe\u7f6e\u4e3a DBNull.Value\n                int? age = null;  \/\/ \u6a21\u62df\u4e00\u4e2a\u53ef\u80fd\u4e3a null \u7684\u503c\n\n                nameParam.Value = \"John Doe\";  \/\/ \u8bbe\u7f6e\u6b63\u5e38\u7684\u975e\u7a7a\u503c\n                ageParam.Value = (age.HasValue) ? (object)age.Value : DBNull.Value;  \/\/ \u5982\u679c age \u662f null\uff0c\u5219\u5206\u914d DBNull.Value\n\n                \/\/ \u5c06\u53c2\u6570\u6dfb\u52a0\u5230\u547d\u4ee4\u4e2d\n                cmd.Parameters.Add(nameParam);\n                cmd.Parameters.Add(ageParam);\n\n                \/\/ \u6267\u884c\u547d\u4ee4\n                cmd.ExecuteNonQuery();\n            }\n        }\n    }\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0c\u5982\u679c <code>age<\/code> \u4e3a <code>null<\/code>\uff0c\u5219\u4f7f\u7528 <code>DBNull.Value<\/code> \u5c06\u5176\u4f20\u9012\u7ed9 SQL Server\u3002\u5426\u5219\uff0c\u5c06 <code>age<\/code> \u7684\u5b9e\u9645\u503c\u4f20\u9012\u7ed9\u547d\u4ee4\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">2. \u4f7f\u7528 <code>SqlParameter<\/code> \u7684 <code>IsDBNull<\/code> \u5c5e\u6027<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">\u6709\u65f6\uff0c\u4f20\u9012 <code>DBNull.Value<\/code> \u9700\u8981\u5728\u5904\u7406\u4e4b\u524d\u505a\u4e00\u4e9b\u989d\u5916\u7684\u903b\u8f91\u5224\u65ad\u3002\u53ef\u4ee5\u901a\u8fc7 <code>SqlParameter<\/code> \u7684 <code>IsDBNull<\/code> \u5c5e\u6027\u6765\u68c0\u67e5\u548c\u5904\u7406\u503c\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u793a\u4f8b\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>SqlParameter ageParam = new SqlParameter(\"@Age\", SqlDbType.Int);\nint? age = null;  \/\/ \u6a21\u62df\u53ef\u80fd\u4e3a\u7a7a\u7684\u503c\n\n\/\/ \u68c0\u67e5\u662f\u5426\u4e3a null \u5e76\u8d4b\u503c\u4e3a DBNull.Value\nageParam.Value = age.HasValue ? (object)age.Value : DBNull.Value;<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\">3. \u4f7f\u7528 <code>DBNull.Value<\/code> \u5904\u7406\u53ef\u7a7a\u7c7b\u578b\uff08\u5982 <code>int?<\/code>, <code>DateTime?<\/code> \u7b49\uff09<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">\u5bf9\u4e8e\u53ef\u7a7a\u7c7b\u578b\uff08<code>Nullable&lt;T&gt;<\/code>\uff09\uff0c\u5f53\u5b83\u4e3a <code>null<\/code> \u65f6\uff0c\u9700\u8981\u663e\u5f0f\u5730\u5c06\u5176\u8f6c\u6362\u4e3a <code>DBNull.Value<\/code>\uff0c\u8fd9\u6837 SQL \u53c2\u6570\u624d\u80fd\u6b63\u786e\u5904\u7406\u5b83\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u793a\u4f8b\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>public void AddEmployee(string name, int? age)\n{\n    using (SqlConnection conn = new SqlConnection(\"your_connection_string\"))\n    {\n        conn.Open();\n        string query = \"INSERT INTO Employees (Name, Age) VALUES (@Name, @Age)\";\n        using (SqlCommand cmd = new SqlCommand(query, conn))\n        {\n            \/\/ \u521b\u5efa SqlParameter\n            cmd.Parameters.Add(new SqlParameter(\"@Name\", SqlDbType.NVarChar) { Value = name });\n            cmd.Parameters.Add(new SqlParameter(\"@Age\", SqlDbType.Int)\n            {\n                Value = age.HasValue ? (object)age.Value : DBNull.Value\n            });\n\n            cmd.ExecuteNonQuery();\n        }\n    }\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728\u8fd9\u91cc\uff0c<code>age.HasValue ? (object)age.Value : DBNull.Value<\/code> \u786e\u4fdd\u4e86\u5982\u679c <code>age<\/code> \u662f <code>null<\/code>\uff0c\u5219\u4f7f\u7528 <code>DBNull.Value<\/code>\uff0c\u5426\u5219\u4f20\u9012\u5b9e\u9645\u503c\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">4. \u5904\u7406\u4e0d\u540c\u7684\u6570\u636e\u5e93\u7c7b\u578b<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">\u786e\u4fdd <code>SqlParameter<\/code> \u7684\u7c7b\u578b\u4e0e\u6570\u636e\u5e93\u5217\u7c7b\u578b\u5339\u914d\u3002\u4f8b\u5982\uff0c\u5982\u679c\u6570\u636e\u5e93\u5217\u5141\u8bb8 <code>NULL<\/code> \u4e14\u7c7b\u578b\u662f <code>INT<\/code>\uff0c\u5219\u4f7f\u7528 <code>SqlDbType.Int<\/code>\uff0c\u5982\u679c\u662f <code>DateTime<\/code> \u7c7b\u578b\uff0c\u4f7f\u7528 <code>SqlDbType.DateTime<\/code>\uff0c\u7b49\u7b49\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">5. \u5bf9\u4e8e <code>NULL<\/code> \u5b57\u7b26\u4e32\uff0c\u53ef\u4ee5\u76f4\u63a5\u4f20\u9012 <code>null<\/code><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">\u5bf9\u4e8e\u5b57\u7b26\u4e32\u7c7b\u578b\uff0cC# \u7684 <code>null<\/code> \u53ef\u4ee5\u76f4\u63a5\u4f20\u9012\u7ed9 SQL <code>NULL<\/code>\uff0c\u56e0\u6b64\u5982\u679c\u4f60\u9700\u8981\u5c06\u7a7a\u5b57\u7b26\u4e32\u4f20\u9012\u4e3a <code>NULL<\/code>\uff0c\u53ef\u4ee5\u76f4\u63a5\u8d4b\u503c <code>null<\/code> \u7ed9\u53c2\u6570\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u793a\u4f8b\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>SqlParameter nameParam = new SqlParameter(\"@Name\", SqlDbType.NVarChar);\nnameParam.Value = (string.IsNullOrEmpty(name)) ? DBNull.Value : name;<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u8fd9\u5c06\u628a\u7a7a\u5b57\u7b26\u4e32\u6216 <code>null<\/code> \u4f20\u9012\u4e3a\u6570\u636e\u5e93\u4e2d\u7684 <code>NULL<\/code> \u503c\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">6. \u4f7f\u7528 <code>Nullable<\/code> \u7c7b\u578b\u4e0e <code>DBNull<\/code><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">\u5bf9\u4e8e <code>Nullable&lt;T&gt;<\/code> \u7c7b\u578b\uff08\u4f8b\u5982 <code>int?<\/code>\u3001<code>DateTime?<\/code>\uff09\uff0c\u5728\u6784\u9020 SQL \u53c2\u6570\u65f6\uff0c\u53ef\u4ee5\u901a\u8fc7 <code>Nullable.HasValue<\/code> \u5224\u65ad\u662f\u5426\u4e3a <code>null<\/code>\uff0c\u5982\u679c\u662f <code>null<\/code>\uff0c\u5219\u8d4b\u503c\u4e3a <code>DBNull.Value<\/code>\uff0c\u5426\u5219\u8d4b\u503c\u4e3a\u5b9e\u9645\u503c\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u793a\u4f8b\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>DateTime? orderDate = null;  \/\/ \u53ef\u7a7a\u7684 DateTime \u7c7b\u578b\nSqlParameter orderDateParam = new SqlParameter(\"@OrderDate\", SqlDbType.DateTime);\norderDateParam.Value = orderDate.HasValue ? (object)orderDate.Value : DBNull.Value;<\/code><\/pre>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<h3 class=\"wp-block-heading\">\u6211\u4eec\u5c06\u8fdb\u4e00\u6b65\u63a2\u8ba8\u53ef\u7a7a\u7c7b\u578b\u3001\u5982\u4f55\u5904\u7406\u591a\u4e2a\u53c2\u6570\u3001\u5982\u4f55\u5728\u5b58\u50a8\u8fc7\u7a0b\u4e2d\u4f7f\u7528\u8fd9\u4e9b\u53c2\u6570\u4ee5\u53ca\u4e00\u4e9b\u5e38\u89c1\u95ee\u9898\u548c\u89e3\u51b3\u65b9\u6cd5\uff1a<\/h3>\n<\/blockquote>\n\n\n\n<h3 class=\"wp-block-heading\">7. \u4f7f\u7528 <code>SqlParameter<\/code> \u7684 <code>Nullable<\/code> \u7c7b\u578b<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">\u5982\u679c\u4f60\u4f7f\u7528\u7684\u662f\u53ef\u7a7a\u7c7b\u578b\uff08<code>Nullable&lt;T&gt;<\/code>\uff09\uff0c\u4f60\u53ef\u4ee5\u5229\u7528 <code>SqlParameter<\/code> \u7684 <code>Value<\/code> \u5c5e\u6027\u76f4\u63a5\u5904\u7406\u3002\u5bf9\u4e8e\u6240\u6709\u53ef\u7a7a\u7c7b\u578b\uff0c<code>DBNull.Value<\/code> \u7528\u4e8e\u66ff\u4ee3 <code>null<\/code>\uff0c\u5e76\u4e14\u5728 SQL Server \u4e2d\u8868\u793a <code>NULL<\/code>\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u793a\u4f8b\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>using System;\nusing System.Data;\nusing System.Data.SqlClient;\n\npublic class Program\n{\n    public static void Main()\n    {\n        string connectionString = \"your_connection_string\";\n\n        using (SqlConnection conn = new SqlConnection(connectionString))\n        {\n            conn.Open();\n\n            string query = \"INSERT INTO Employees (Name, Age) VALUES (@Name, @Age)\";\n            using (SqlCommand cmd = new SqlCommand(query, conn))\n            {\n                \/\/ \u4f7f\u7528 SqlParameter \u8bbe\u7f6e\u503c\n                SqlParameter nameParam = new SqlParameter(\"@Name\", SqlDbType.NVarChar);\n                SqlParameter ageParam = new SqlParameter(\"@Age\", SqlDbType.Int);\n\n                \/\/ \u5047\u8bbe Age \u4e3a\u53ef\u7a7a\u7c7b\u578b int?\n                int? age = null;  \/\/ \u5982\u679c\u4e3a null\uff0c\u5219\u8868\u793a\u6570\u636e\u5e93\u4e2d\u7684 NULL\n\n                \/\/ \u8bbe\u7f6e\u53c2\u6570\u503c\n                nameParam.Value = \"John Doe\";  \/\/ \u8bbe\u7f6e Name \u4e3a\u975e\u7a7a\u503c\n                ageParam.Value = age.HasValue ? (object)age.Value : DBNull.Value;  \/\/ \u5982\u679c Age \u4e3a null\uff0c\u5219\u8bbe\u7f6e\u4e3a DBNull.Value\n\n                \/\/ \u5c06\u53c2\u6570\u6dfb\u52a0\u5230\u547d\u4ee4\u5bf9\u8c61\u4e2d\n                cmd.Parameters.Add(nameParam);\n                cmd.Parameters.Add(ageParam);\n\n                \/\/ \u6267\u884c SQL \u547d\u4ee4\n                cmd.ExecuteNonQuery();\n            }\n        }\n    }\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0c<code>age<\/code> \u662f\u4e00\u4e2a\u53ef\u7a7a\u7684 <code>int?<\/code> \u7c7b\u578b\u3002\u5f53 <code>age<\/code> \u4e3a <code>null<\/code> \u65f6\uff0c<code>DBNull.Value<\/code> \u4f1a\u88ab\u5206\u914d\u7ed9 <code>SqlParameter<\/code>\uff0c\u800c\u4e0d\u662f <code>null<\/code>\uff0c\u4ece\u800c\u786e\u4fdd SQL Server \u6b63\u786e\u5904\u7406\u5b83\u4e3a <code>NULL<\/code>\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">8. \u5904\u7406\u591a\u4e2a\u53ef\u7a7a\u53c2\u6570<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">\u5f53\u4f60\u5728 SQL \u67e5\u8be2\u4e2d\u4f7f\u7528\u591a\u4e2a\u53ef\u7a7a\u53c2\u6570\u65f6\uff0c\u9700\u8981\u4e3a\u6bcf\u4e2a\u53c2\u6570\u5355\u72ec\u68c0\u67e5 <code>null<\/code> \u503c\uff0c\u5e76\u6839\u636e\u60c5\u51b5\u8d4b\u503c\u4e3a <code>DBNull.Value<\/code> \u6216\u5b9e\u9645\u503c\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u793a\u4f8b\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>using System;\nusing System.Data;\nusing System.Data.SqlClient;\n\npublic class Program\n{\n    public static void Main()\n    {\n        string connectionString = \"your_connection_string\";\n\n        using (SqlConnection conn = new SqlConnection(connectionString))\n        {\n            conn.Open();\n\n            string query = \"INSERT INTO Employees (Name, Age, JoiningDate) VALUES (@Name, @Age, @JoiningDate)\";\n            using (SqlCommand cmd = new SqlCommand(query, conn))\n            {\n                \/\/ \u521b\u5efa SqlParameter\n                SqlParameter nameParam = new SqlParameter(\"@Name\", SqlDbType.NVarChar);\n                SqlParameter ageParam = new SqlParameter(\"@Age\", SqlDbType.Int);\n                SqlParameter joiningDateParam = new SqlParameter(\"@JoiningDate\", SqlDbType.DateTime);\n\n                \/\/ \u5047\u8bbe\u8fd9\u4e9b\u53c2\u6570\u6709\u53ef\u80fd\u4e3a null\n                string name = \"John Doe\";\n                int? age = null;  \/\/ \u5047\u8bbe Age \u4e3a\u7a7a\n                DateTime? joiningDate = null;  \/\/ \u5047\u8bbe JoiningDate \u4e3a\u7a7a\n\n                \/\/ \u8bbe\u7f6e\u53c2\u6570\u7684\u503c\uff0c\u4f7f\u7528 DBNull.Value \u5904\u7406 null\n                nameParam.Value = name ?? DBNull.Value;\n                ageParam.Value = age.HasValue ? (object)age.Value : DBNull.Value;\n                joiningDateParam.Value = joiningDate.HasValue ? (object)joiningDate.Value : DBNull.Value;\n\n                \/\/ \u5c06\u53c2\u6570\u6dfb\u52a0\u5230\u547d\u4ee4\u5bf9\u8c61\u4e2d\n                cmd.Parameters.Add(nameParam);\n                cmd.Parameters.Add(ageParam);\n                cmd.Parameters.Add(joiningDateParam);\n\n                \/\/ \u6267\u884c SQL \u547d\u4ee4\n                cmd.ExecuteNonQuery();\n            }\n        }\n    }\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0c\u6211\u4eec\u5904\u7406\u4e86\u4e09\u4e2a\u53ef\u7a7a\u53c2\u6570 <code>name<\/code>, <code>age<\/code> \u548c <code>joiningDate<\/code>\uff0c\u5e76\u6839\u636e\u662f\u5426\u4e3a <code>null<\/code> \u6765\u8bbe\u7f6e\u76f8\u5e94\u7684\u503c\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">9. \u4f7f\u7528 <code>DBNull.Value<\/code> \u5bf9\u4e8e <code>null<\/code> \u5b57\u7b26\u4e32\u6216 <code>DateTime<\/code> \u503c<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">\u5982\u679c\u4f60\u5728\u6570\u636e\u5e93\u4e2d\u5b58\u50a8\u5b57\u7b26\u4e32\u6216 <code>DateTime<\/code> \u7c7b\u578b\u7684 <code>NULL<\/code>\uff0c\u5f53\u8fd9\u4e9b\u503c\u4e3a <code>null<\/code> \u65f6\uff0c\u4f60\u5e94\u4f7f\u7528 <code>DBNull.Value<\/code>\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u5b57\u7b26\u4e32\u793a\u4f8b\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>SqlParameter nameParam = new SqlParameter(\"@Name\", SqlDbType.NVarChar);\nstring name = null;  \/\/ \u5047\u8bbe Name \u4e3a null\n\nnameParam.Value = string.IsNullOrEmpty(name) ? DBNull.Value : name;<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0c\u5982\u679c <code>name<\/code> \u662f <code>null<\/code> \u6216\u7a7a\u5b57\u7b26\u4e32\uff0c<code>DBNull.Value<\/code> \u5c06\u88ab\u4f20\u9012\u7ed9 SQL Server\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">DateTime \u793a\u4f8b\uff1a<\/h4>\n\n\n\n<pre class=\"wp-block-code\"><code>SqlParameter dateParam = new SqlParameter(\"@Date\", SqlDbType.DateTime);\nDateTime? date = null;  \/\/ \u5047\u8bbe Date \u4e3a null\n\ndateParam.Value = date.HasValue ? (object)date.Value : DBNull.Value;<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5982\u679c <code>date<\/code> \u4e3a <code>null<\/code>\uff0c\u5219\u4f20\u9012 <code>DBNull.Value<\/code> \u7ed9 SQL Server\uff0c\u5426\u5219\u4f20\u9012\u5b9e\u9645\u7684 <code>DateTime<\/code> \u503c\u3002<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">10. \u5904\u7406 <code>NULL<\/code> \u53c2\u6570\u5728\u5b58\u50a8\u8fc7\u7a0b\u4e2d\u7684\u4f7f\u7528<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728\u5b58\u50a8\u8fc7\u7a0b\u4e2d\uff0c\u4f60\u53ef\u4ee5\u4f7f\u7528 <code>NULL<\/code> \u503c\u4f5c\u4e3a\u53c2\u6570\uff0c\u5e76\u5728\u5b58\u50a8\u8fc7\u7a0b\u4e2d\u8fdb\u884c\u6761\u4ef6\u5224\u65ad\u3002C# \u4e2d\u4f20\u9012 <code>NULL<\/code> \u65f6\u4ecd\u7136\u4f7f\u7528 <code>DBNull.Value<\/code>\u3002<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">\u793a\u4f8b\uff1a<\/h4>\n\n\n\n<p class=\"wp-block-paragraph\">\u5047\u8bbe\u5b58\u50a8\u8fc7\u7a0b <code>InsertEmployee<\/code> \u6709\u4e00\u4e2a\u53ef\u9009\u7684 <code>Age<\/code> \u53c2\u6570\uff0c\u5b83\u53ef\u4ee5\u662f <code>NULL<\/code>\uff0c\u4f60\u9700\u8981\u5728\u8c03\u7528\u5b58\u50a8\u8fc7\u7a0b\u65f6\u4f20\u9012 <code>NULL<\/code> \u503c\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>CREATE PROCEDURE InsertEmployee\n    @Name NVARCHAR(100),\n    @Age INT = NULL\nAS\nBEGIN\n    INSERT INTO Employees (Name, Age)\n    VALUES (@Name, @Age);\nEND<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u8c03\u7528\u5b58\u50a8\u8fc7\u7a0b\u65f6\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>using (SqlCommand cmd = new SqlCommand(\"InsertEmployee\", conn))\n{\n    cmd.CommandType = CommandType.StoredProcedure;\n\n    SqlParameter nameParam = new SqlParameter(\"@Name\", SqlDbType.NVarChar);\n    SqlParameter ageParam = new SqlParameter(\"@Age\", SqlDbType.Int);\n\n    string name = \"John Doe\";\n    int? age = null;  \/\/ \u5047\u8bbe Age \u4e3a null\n\n    nameParam.Value = name;\n    ageParam.Value = age.HasValue ? (object)age.Value : DBNull.Value;  \/\/ \u5982\u679c\u4e3a null\uff0c\u5219\u4f20\u9012 DBNull.Value\n\n    cmd.Parameters.Add(nameParam);\n    cmd.Parameters.Add(ageParam);\n\n    cmd.ExecuteNonQuery();\n}<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\">11. \u901a\u8fc7\u53c2\u6570\u7c7b\u578b\u52a8\u6001\u8bbe\u7f6e <code>DBNull.Value<\/code><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">\u6709\u65f6\u4f60\u53ef\u80fd\u4e0d\u6e05\u695a\u53c2\u6570\u7684\u7c7b\u578b\uff0c\u53ef\u4ee5\u901a\u8fc7\u68c0\u67e5\u53c2\u6570\u7684\u7c7b\u578b\u6765\u52a8\u6001\u8bbe\u7f6e <code>DBNull.Value<\/code>\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>public void SetSqlParameter(SqlParameter param, object value)\n{\n    if (value == null)\n    {\n        param.Value = DBNull.Value;  \/\/ \u5982\u679c\u4e3a null\uff0c\u5219\u8bbe\u7f6e\u4e3a DBNull.Value\n    }\n    else\n    {\n        param.Value = value;  \/\/ \u5426\u5219\u4f20\u9012\u5b9e\u9645\u503c\n    }\n}<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\">12. \u5e38\u89c1\u95ee\u9898\u548c\u89e3\u51b3\u65b9\u6cd5<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u95ee\u9898\uff1aSQL Server \u8fd4\u56de\u9519\u8bef &#8220;Cannot insert the value NULL into column&#8221;<\/strong><\/li>\n\n\n\n<li>\u89e3\u51b3\u65b9\u6cd5\uff1a\u786e\u4fdd\u5728\u6570\u636e\u5e93\u5217\u4e0a\u8bbe\u7f6e\u4e86 <code>NULL<\/code> \u5141\u8bb8\u9009\u9879\u3002\u5982\u679c\u5217\u4e0d\u5141\u8bb8 <code>NULL<\/code>\uff0c\u90a3\u4e48\u5fc5\u987b\u4f20\u9012\u4e00\u4e2a\u6709\u6548\u503c\uff0c\u4e0d\u80fd\u4f20\u9012 <code>DBNull.Value<\/code>\u3002<\/li>\n\n\n\n<li><strong>\u95ee\u9898\uff1a<code>DBNull<\/code> \u4e0d\u80fd\u4e0e <code>NULL<\/code> \u505a\u6bd4\u8f83<\/strong><\/li>\n\n\n\n<li>\u89e3\u51b3\u65b9\u6cd5\uff1a\u786e\u4fdd\u5728 SQL \u67e5\u8be2\u4e2d\u6b63\u786e\u4f7f\u7528 <code>IS NULL<\/code> \u6216 <code>IS NOT NULL<\/code> \u6765\u5224\u65ad <code>NULL<\/code> \u503c\u3002\u907f\u514d\u4f7f\u7528 <code>=<\/code> \u6765\u6bd4\u8f83 <code>NULL<\/code> \u503c\u3002<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">\u603b\u7ed3<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728 C# \u4e2d\u4e0e SQL Server \u4ea4\u4e92\u65f6\uff0c\u5f53\u4f20\u9012\u53ef\u7a7a\u53c2\u6570\uff08\u4f8b\u5982 <code>int?<\/code>\u3001<code>DateTime?<\/code>\uff09\u65f6\uff0c\u6b63\u786e\u5730\u4f7f\u7528 <code>DBNull.Value<\/code> \u6765\u8868\u793a\u6570\u636e\u5e93\u4e2d\u7684 <code>NULL<\/code> \u975e\u5e38\u91cd\u8981\u3002\u901a\u8fc7\u4f7f\u7528 <code>DBNull.Value<\/code>\uff0c\u4f60\u53ef\u4ee5\u786e\u4fdd SQL Server \u6b63\u786e\u5730\u63a5\u6536\u5230 <code>NULL<\/code> \u503c\uff0c\u5e76\u907f\u514d\u51fa\u73b0\u7c7b\u578b\u8f6c\u6362\u9519\u8bef\u3002\u5bf9\u4e8e\u6240\u6709\u53ef\u80fd\u4e3a <code>null<\/code> \u7684\u5b57\u6bb5\uff0c\u90fd\u9700\u8981\u663e\u5f0f\u5730\u68c0\u67e5\u5e76\u8d4b\u503c\u4e3a <code>DBNull.Value<\/code>\uff0c\u4ee5\u786e\u4fdd\u67e5\u8be2\u6216\u5b58\u50a8\u8fc7\u7a0b\u6b63\u786e\u5904\u7406\u8fd9\u4e9b\u503c\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u5728 C# \u4e2d\uff0c\u5c06 NULL \u503c\u6b63\u786e\u5730\u5206\u914d\u7ed9 SqlParameter \u65f6\uff0c\u786e\u4fdd\u4f20\u9012\u7684\u53c2\u6570\u80fd\u591f\u8bc6\u522b NULL \u503c [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[59],"tags":[],"class_list":["post-804","post","type-post","status-publish","format-standard","hentry","category-c"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/804","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/comments?post=804"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/804\/revisions"}],"predecessor-version":[{"id":805,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/804\/revisions\/805"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=804"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=804"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=804"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}