{"id":1890,"date":"2019-06-22T16:14:40","date_gmt":"2019-06-22T08:14:40","guid":{"rendered":"https:\/\/coderbee.net\/?p=1890"},"modified":"2019-06-22T16:14:40","modified_gmt":"2019-06-22T08:14:40","slug":"oracle-rownum-%e4%b8%8e-offset","status":"publish","type":"post","link":"https:\/\/coderbee.net\/index.php\/db\/20190622\/1890","title":{"rendered":"Oracle rownum \u4e0e offset"},"content":{"rendered":"<p>\u4e3b\u8981\u6765\u81ea\uff1a<br \/>\n<a href=\"https:\/\/blogs.oracle.com\/oraclemagazine\/on-rownum-and-limiting-results\">On ROWNUM and Limiting Results<\/a><br \/>\n<a href=\"https:\/\/docs.oracle.com\/javadb\/10.8.3.0\/ref\/rrefsqljoffsetfetch.html\">The result offset and fetch first clauses<\/a><\/p>\n<h1>rownum<\/h1>\n<h2>rownum \u4e3b\u8981\u6709\u4e24\u7c7b\u7528\u5904<\/h2>\n<ul>\n<li>\u5904\u7406 top N \uff1b<\/li>\n<li>\u5206\u9875\u67e5\u8be2\uff1b<\/li>\n<\/ul>\n<h2>rownum \u7684\u5de5\u4f5c\u673a\u5236<\/h2>\n<p>rownum \u662f\u67e5\u8be2\u4e2d\u7684\u4f2a\u5217\uff0c\u4ece 1 \u5f00\u59cb\u8ba1\u6570\u3002<\/p>\n<blockquote>\n<p>A ROWNUM value is assigned to a row after it passes the predicate phase of the query but before the query does any sorting or aggregation. Also, a ROWNUM value is incremented only after it is assigned .<\/p>\n<\/blockquote>\n<p>rownum \u7684\u503c\u662f\u5728\u884c\u8bb0\u5f55\u901a\u8fc7\u4e86\u67e5\u8be2\u7684\u8fc7\u6ee4\u9636\u6bb5\u3001\u5728\u6392\u5e8f\u6216\u805a\u5408\u4e4b\u524d\u88ab\u8d4b\u503c\u3002rownum \u53ea\u6709\u5728\u88ab\u8d4b\u503c\u4e4b\u540e\u624d\u4f1a\u9012\u589e\u3002<code>select * from t where ROWNUM &gt; 1;<\/code> \u662f\u6c38\u8fdc\u67e5\u4e0d\u5230\u8bb0\u5f55\u7684\u3002<\/p>\n<p>\u67e5\u8be2\u7684\u5904\u7406\u6b65\u9aa4\u5927\u6982\u5982\u4e0b\uff1a<br \/>\n1. from\/where \u9996\u5148\u6267\u884c\uff1b<br \/>\n2. rownum \u88ab\u9012\u589e\u3001\u8d4b\u503c\u7ed9 from\/where \u5b50\u53e5\u8f93\u51fa\u7684\u6bcf\u4e00\u884c\uff1b<br \/>\n3. \u6267\u884c select \u5b50\u53e5\uff1b<br \/>\n4. \u6267\u884c group by \u5b50\u53e5\uff1b<br \/>\n5. \u6267\u884c having \uff1b<br \/>\n6. \u6267\u884c order by \u3002<\/p>\n<p><!--more--><\/p>\n<p>top N \u67e5\u8be2\u7684\u6b63\u786e\u5199\u6cd5\uff1a<br \/>\n<code>select * from (select * from emp order by sal desc) where ROWNUM &lt;= 5;<\/code><\/p>\n<p>Oracle \u5bf9\u8fd9\u7c7b rownum top N \u67e5\u8be2\u6709\u4e2a\u4f18\u5316\uff0c\u4e0d\u4f1a\u6392\u5e8f\u6574\u4e2a\u7ed3\u679c\u96c6\uff0c\u800c\u662f\u5229\u7528 N \u4e2a\u5143\u7d20\u7684\u6570\u7ec4\u7a7a\u95f4\u8fdb\u884c\u6392\u5e8f\uff0c\u8282\u7701\u4e86\u6392\u5e8f\u9700\u8981\u7684\u7a7a\u95f4\uff08\u5982\u679c\u7ed3\u679c\u96c6\u592a\u5927\uff0c\u8fd8\u5f97\u501f\u52a9\u78c1\u76d8\u8fdb\u884c\u6392\u5e8f\uff09\u3002<\/p>\n<p>\u5206\u9875\u7684\u901a\u7528\u5199\u6cd5\uff1a<\/p>\n<pre><code class=\"sql\">select *\n  from (select \/*+ FIRST_ROWS(n) *\/\n         a.*, ROWNUM rnum\n          from (your_query_goes_here, with order by) a\n         where ROWNUM &lt;= :MAX_ROW_TO_FETCH)\n where rnum &gt;= :MIN_ROW_TO_FETCH;\n<\/code><\/pre>\n<p>\u8fd9\u4e2a\u5199\u6cd5\u4f1a\u53d7\u76ca\u4e8e\u524d\u9762\u63d0\u5230\u7684 top N \u4f18\u5316\u3002<br \/>\n<strong>\u6ce8\u610f\uff1a<\/strong>\u8fd9\u4e2a\u5206\u9875\u67e5\u8be2\u7684 order by \u8bed\u53e5\u5e94\u8be5\u57fa\u4e8e\u552f\u4e00\u6027\u7684\u5217\u8fdb\u884c\u6392\u5e8f\uff0c\u5982\u679c\u6392\u5e8f\u5217\u7684\u91cd\u590d\u503c\u592a\u591a\uff0c\u6392\u5e8f\u7684\u7ed3\u679c\u53ef\u80fd\u4f1a\u6df7\u4e71\u3002<\/p>\n<h2>offset<\/h2>\n<p>\u5728 Oracle 12c\uff0c\u53ef\u4ee5\u901a\u8fc7 offset \u8fdb\u884c\u5206\u9875\uff1a<\/p>\n<p>offset \u8bed\u6cd5\uff1a<\/p>\n<pre><code>OFFSET { integer-literal | ? } {ROW | ROWS}\nFETCH { FIRST | NEXT } [integer-literal | ? ] {ROW | ROWS} ONLY\n<\/code><\/pre>\n<p>\u7b2c\u4e00\u6761\u8bb0\u5f55\u7684 offset \u662f 0\u3002\u5982\u679c\u6ca1\u6709\u4e0e order by \u5b50\u53e5\u4e00\u8d77\u4f7f\u7528\uff0c\u5219\u7ed3\u679c\u7684\u987a\u5e8f\u4e00\u822c\u662f\u8bb0\u5f55\u63d2\u5165\u7684\u987a\u5e8f\u3002<\/p>\n<pre><code class=\"sql\">-- \u8868\u793a\u4ece\u7b2c20\u6761\u5f00\u59cb\u53d6\u4e0b10\u6761\u8bb0\u5f55\nSELECT * \nFROM sometable\nORDER BY name\nOFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY;\n\n\n-- \u8df3\u8fc7\u524d 100 \u884c\uff0c\u5982\u679c\u8868\u5c11\u4e8e 101 \u6761\u8bb0\u5f55\uff0c\u7ed3\u679c\u96c6\u5c06\u662f\u7a7a\u7684\nSELECT * FROM T OFFSET 100 ROWS;\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"<p>\u4e3b\u8981\u6765\u81ea\uff1a On ROWNUM and Limiting Results The &hellip; <a href=\"https:\/\/coderbee.net\/index.php\/db\/20190622\/1890\">\u7ee7\u7eed\u9605\u8bfb <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23],"tags":[315,314,289],"_links":{"self":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/1890"}],"collection":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/comments?post=1890"}],"version-history":[{"count":1,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/1890\/revisions"}],"predecessor-version":[{"id":1891,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/1890\/revisions\/1891"}],"wp:attachment":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/media?parent=1890"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/categories?post=1890"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/tags?post=1890"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}