{"id":802,"date":"2025-01-11T00:13:30","date_gmt":"2025-01-10T16:13:30","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=802"},"modified":"2025-01-11T00:13:30","modified_gmt":"2025-01-10T16:13:30","slug":"%e5%9c%a8-sql-server-%e4%b8%ad%ef%bc%8c%e5%a4%84%e7%90%86%e5%8f%af%e4%b8%ba%e7%a9%ba%e7%9a%84%e5%8f%82%e6%95%b0%e6%97%b6%ef%bc%8c%e5%a6%82%e4%bd%95%e8%a7%a3%e5%86%b3%e6%b2%a1%e6%9c%89","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/01\/11\/%e5%9c%a8-sql-server-%e4%b8%ad%ef%bc%8c%e5%a4%84%e7%90%86%e5%8f%af%e4%b8%ba%e7%a9%ba%e7%9a%84%e5%8f%82%e6%95%b0%e6%97%b6%ef%bc%8c%e5%a6%82%e4%bd%95%e8%a7%a3%e5%86%b3%e6%b2%a1%e6%9c%89\/","title":{"rendered":"\u5728 SQL Server \u4e2d\uff0c\u5904\u7406\u53ef\u4e3a\u7a7a\u7684\u53c2\u6570\u65f6\uff0c\u5982\u4f55\u89e3\u51b3\u201c\u6ca1\u6709\u4ece DBNull \u5230 int \u7684\u9690\u5f0f\u8f6c\u6362\u201d\u9519\u8bef"},"content":{"rendered":"\n
\n

\u5728 SQL Server \u4e2d\uff0c\u5904\u7406\u53ef\u4e3a\u7a7a\u7684\u53c2\u6570\u65f6\uff0c\u5982\u679c\u53c2\u6570\u7684\u503c\u4e3a NULL<\/code>\uff0c\u800c\u4f60\u5c1d\u8bd5\u5c06\u5176\u8f6c\u6362\u4e3a\u975e\u7a7a\u7c7b\u578b\uff08\u6bd4\u5982 int<\/code>\uff09\uff0c\u5c31\u53ef\u80fd\u4f1a\u9047\u5230\u7c7b\u4f3c \u201c\u6ca1\u6709\u4ece DBNull \u5230 int \u7684\u9690\u5f0f\u8f6c\u6362\u201d<\/strong> \u7684\u9519\u8bef\u3002\u8fd9\u901a\u5e38\u662f\u56e0\u4e3a NULL<\/code> \u503c\u4e0d\u80fd\u76f4\u63a5\u4e0e\u975e\u7a7a\u7c7b\u578b\u8fdb\u884c\u6bd4\u8f83\u6216\u8fd0\u7b97\u3002<\/p>\n<\/blockquote>\n\n\n\n

\u8981\u907f\u514d\u8fd9\u4e2a\u9519\u8bef\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u51e0\u79cd\u65b9\u6cd5\uff1a<\/p>\n\n\n\n

\n\n\n\n

1. \u4f7f\u7528 IS NULL<\/code> \u6216 IS NOT NULL<\/code> \u660e\u786e\u68c0\u67e5 NULL<\/code><\/h3>\n\n\n\n

\u5728 SQL \u67e5\u8be2\u4e2d\u663e\u5f0f\u68c0\u67e5\u53c2\u6570\u662f\u5426\u4e3a NULL<\/code>\uff0c\u907f\u514d NULL<\/code> \u88ab\u9690\u5f0f\u8f6c\u6362\u4e3a\u5176\u4ed6\u7c7b\u578b\u3002<\/p>\n\n\n\n

\u793a\u4f8b\uff1a<\/h4>\n\n\n\n
DECLARE @param INT = NULL;  -- \u6a21\u62df\u4e00\u4e2a\u53ef\u80fd\u4e3a\u7a7a\u7684\u53c2\u6570\n\nSELECT *\nFROM Employees\nWHERE (@param IS NULL OR DepartmentID = @param);<\/code><\/pre>\n\n\n\n
\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0c@param<\/code> \u5982\u679c\u662f NULL<\/code>\uff0c\u67e5\u8be2\u5c06\u4e0d\u4f1a\u5c1d\u8bd5\u5c06\u5b83\u4e0e DepartmentID<\/code> \u8fdb\u884c\u6bd4\u8f83\uff0c\u800c\u662f\u76f4\u63a5\u8fd4\u56de\u6240\u6709\u8bb0\u5f55\u3002<\/p>\n\n\n\n
2. \u4f7f\u7528 COALESCE<\/code> \u6216 ISNULL<\/code> \u51fd\u6570<\/h3>\n\n\n\n
COALESCE<\/code> \u548c ISNULL<\/code> \u51fd\u6570\u53ef\u4ee5\u7528\u6765\u5c06 NULL<\/code> \u503c\u66ff\u6362\u4e3a\u4e00\u4e2a\u9ed8\u8ba4\u503c\uff0c\u907f\u514d NULL<\/code> \u4e0e\u5176\u4ed6\u6570\u636e\u7c7b\u578b\u76f4\u63a5\u6bd4\u8f83\u65f6\u51fa\u9519\u3002<\/p>\n\n\n\n
\u793a\u4f8b\uff1a<\/h4>\n\n\n\n
DECLARE @param INT = NULL;  -- \u6a21\u62df\u4e00\u4e2a\u53ef\u80fd\u4e3a\u7a7a\u7684\u53c2\u6570\n\nSELECT *\nFROM Employees\nWHERE DepartmentID = COALESCE(@param, DepartmentID);<\/code><\/pre>\n\n\n\n
\u6216\u8005\u4f7f\u7528 ISNULL<\/code>\uff1a<\/p>\n\n\n\n
DECLARE @param INT = NULL;  -- \u6a21\u62df\u4e00\u4e2a\u53ef\u80fd\u4e3a\u7a7a\u7684\u53c2\u6570\n\nSELECT *\nFROM Employees\nWHERE DepartmentID = ISNULL(@param, DepartmentID);<\/code><\/pre>\n\n\n\n
\u8fd9\u6837\uff0c\u5982\u679c @param<\/code> \u4e3a NULL<\/code>\uff0c\u67e5\u8be2\u5c06\u81ea\u52a8\u4f7f\u7528 DepartmentID<\/code> \u7684\u503c\u8fdb\u884c\u6bd4\u8f83\u3002<\/p>\n\n\n\n
3. \u5bf9\u53ef\u7a7a\u53c2\u6570\u4f7f\u7528 NULL<\/code> \u5904\u7406\u903b\u8f91<\/h3>\n\n\n\n
\u5982\u679c\u4f60\u77e5\u9053\u67d0\u4e2a\u53c2\u6570\u662f\u53ef\u7a7a\u7684\uff0c\u5e76\u4e14\u5b83\u7684\u503c\u53ef\u80fd\u4e3a NULL<\/code>\uff0c\u53ef\u4ee5\u5728\u5b58\u50a8\u8fc7\u7a0b\u4e2d\u6216\u8005\u5e94\u7528\u7a0b\u5e8f\u4e2d\u5148\u5904\u7406\u8fd9\u4e2a NULL<\/code>\uff0c\u7136\u540e\u518d\u4f20\u9012\u7ed9 SQL \u67e5\u8be2\u3002\u6bd4\u5982\uff0c\u5728\u5e94\u7528\u7a0b\u5e8f\u4ee3\u7801\u4e2d\u901a\u8fc7\u68c0\u67e5\u53c2\u6570\u662f\u5426\u4e3a NULL<\/code> \u6765\u51b3\u5b9a\u5982\u4f55\u6784\u9020 SQL \u67e5\u8be2\u3002<\/p>\n\n\n\n
\u793a\u4f8b\uff1a<\/h4>\n\n\n\n
\u5047\u8bbe\u5728\u5e94\u7528\u7a0b\u5e8f\u4e2d\u68c0\u67e5 param<\/code> \u662f\u5426\u4e3a\u7a7a\uff1a<\/p>\n\n\n\n
if (param == null)\n{\n    sqlQuery = \"SELECT * FROM Employees\";\n}\nelse\n{\n    sqlQuery = \"SELECT * FROM Employees WHERE DepartmentID = @param\";\n}<\/code><\/pre>\n\n\n\n
4. \u5bf9\u4e8e\u52a8\u6001\u67e5\u8be2\uff0c\u4f7f\u7528 NULLIF<\/code> \u6216 CASE<\/code> \u8bed\u53e5<\/h3>\n\n\n\n
\u5728\u6784\u9020\u67e5\u8be2\u65f6\uff0c\u53ef\u4ee5\u4f7f\u7528 NULLIF<\/code> \u6216 CASE<\/code> \u6765\u5904\u7406 NULL<\/code> \u53c2\u6570\u3002<\/p>\n\n\n\n
\u793a\u4f8b\uff1a<\/h4>\n\n\n\n
DECLARE @param INT = NULL;  -- \u6a21\u62df\u4e00\u4e2a\u53ef\u80fd\u4e3a\u7a7a\u7684\u53c2\u6570\n\nSELECT *\nFROM Employees\nWHERE DepartmentID = CASE WHEN @param IS NULL THEN DepartmentID ELSE @param END;<\/code><\/pre>\n\n\n\n
\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0c\u5982\u679c @param<\/code> \u662f NULL<\/code>\uff0c\u67e5\u8be2\u5c06\u4f1a\u5ffd\u7565 DepartmentID<\/code> \u7684\u503c\uff0c\u5b9e\u9645\u4e0a\u67e5\u8be2\u6240\u6709\u7684\u8bb0\u5f55\u3002\u5982\u679c @param<\/code> \u6709\u503c\uff0c\u5219\u4f7f\u7528\u5b83\u8fdb\u884c\u8fc7\u6ee4\u3002<\/p>\n\n\n\n
\n\n\n\n
\u603b\u7ed3<\/h3>\n\n\n\n
\u8981\u907f\u514d\u201c\u6ca1\u6709\u4ece DBNull<\/code> \u5230 int<\/code> \u7684\u9690\u5f0f\u8f6c\u6362\u201d\u9519\u8bef\uff0c\u4f60\u9700\u8981\u660e\u786e\u5904\u7406 NULL<\/code> \u503c\uff0c\u5728 SQL \u67e5\u8be2\u4e2d\u907f\u514d\u5c06 NULL<\/code> \u4e0e\u975e\u7a7a\u503c\u8fdb\u884c\u76f4\u63a5\u6bd4\u8f83\u3002\u5e38\u89c1\u7684\u505a\u6cd5\u6709\uff1a<\/p>\n\n\n\n
    \n
  • \u4f7f\u7528 IS NULL<\/code> \u6216 IS NOT NULL<\/code> \u8fdb\u884c\u663e\u5f0f\u68c0\u67e5\u3002<\/li>\n\n\n\n
  • \u4f7f\u7528 COALESCE<\/code> \u6216 ISNULL<\/code> \u51fd\u6570\u4e3a NULL<\/code> \u53c2\u6570\u63d0\u4f9b\u9ed8\u8ba4\u503c\u3002<\/li>\n\n\n\n
  • \u5728\u5e94\u7528\u7a0b\u5e8f\u4e2d\u5904\u7406 NULL<\/code> \u53c2\u6570\uff0c\u786e\u4fdd\u67e5\u8be2\u6784\u9020\u6b63\u786e\u3002<\/li>\n<\/ul>\n\n\n\n
    \u8fd9\u6837\uff0c\u4f60\u5c31\u80fd\u907f\u514d\u9690\u5f0f\u8f6c\u6362\u9519\u8bef\uff0c\u5e76\u786e\u4fdd SQL \u67e5\u8be2\u5728\u5904\u7406\u53ef\u7a7a\u53c2\u6570\u65f6\u6b63\u5e38\u8fd0\u884c\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
    \u5728 SQL Server \u4e2d\uff0c\u5904\u7406\u53ef\u4e3a\u7a7a\u7684\u53c2\u6570\u65f6\uff0c\u5982\u679c\u53c2\u6570\u7684\u503c\u4e3a NULL\uff0c\u800c\u4f60\u5c1d\u8bd5\u5c06\u5176\u8f6c\u6362\u4e3a\u975e\u7a7a\u7c7b\u578b\uff08\u6bd4\u5982  […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[35],"tags":[],"class_list":["post-802","post","type-post","status-publish","format-standard","hentry","category-mysql"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/802","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=802"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/802\/revisions"}],"predecessor-version":[{"id":803,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/802\/revisions\/803"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=802"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=802"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=802"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}