{"id":242,"date":"2015-06-24T07:37:57","date_gmt":"2015-06-24T07:37:57","guid":{"rendered":"http:\/\/blog.tiran.info\/?p=242"},"modified":"2015-06-24T07:37:57","modified_gmt":"2015-06-24T07:37:57","slug":"echantillonnage-sous-oracle","status":"publish","type":"post","link":"https:\/\/blog.tiran.stream\/?p=242","title":{"rendered":"Echantillonnage sous Oracle"},"content":{"rendered":"<p style=\"text-align: justify;\">La clause <a href=\"http:\/\/docs.oracle.com\/database\/121\/SQLRF\/statements_10002.htm#SQLRF01702\" target=\"_blank\">SAMPLE<\/a> de l&rsquo;ordre SELECT permet de r\u00e9aliser un <a href=\"https:\/\/fr.wikipedia.org\/wiki\/%C3%89chantillon_(statistiques)\" target=\"_blank\">\u00e9chantillonnage <\/a>al\u00e9atoire des donn\u00e9es d&rsquo;une table. Le nombre de lignes retourn\u00e9es correspond approximativement au pourcentage pass\u00e9 en argument.<br \/>\nDans l&rsquo;exemple ci-dessous, on pr\u00e9l\u00e8ve \u00e0 deux reprises al\u00e9atoirement 0.1% de la table COMMANDES. On peut noter la fluctuation du nombre de lignes restitu\u00e9es 253 &amp; 237:<\/p>\n<pre>SQL&gt; set NUMFORMAT 9999.99\nSQL&gt; \nSQL&gt; SELECT AVG (montant), STDDEV_SAMP (montant), COUNT (*)\n  2    FROM commandes SAMPLE (0.1);\n\nAVG(MONTANT) STDDEV_SAMP(MONTANT) COUNT(*)\n------------ -------------------- --------\n      990.91                98.99   253.00\n\nSQL&gt; \/\n\nAVG(MONTANT) STDDEV_SAMP(MONTANT) COUNT(*)\n------------ -------------------- --------\n     1008.35                99.77   237.00\n\nSQL&gt; \n<\/pre>\n<p style=\"text-align: justify;\">SAMPLE accepte aussi une clause optionnelle SEED qui permet de garantir la r\u00e9p\u00e9tabilit\u00e9 de l&rsquo;\u00e9chantillonnage (utile dans des cas de test):<\/p>\n<pre>SQL&gt; SELECT AVG (montant), STDDEV_SAMP (montant), COUNT (*)\n  2    FROM commandes SAMPLE (0.1) SEED (1234);\n\nAVG(MONTANT) STDDEV_SAMP(MONTANT) COUNT(*)\n------------ -------------------- --------\n     1016.87                98.90   247.00\n\nSQL&gt; \/\n\nAVG(MONTANT) STDDEV_SAMP(MONTANT) COUNT(*)\n------------ -------------------- --------\n     1016.87                98.90   247.00\n\nSQL&gt;\n\n\n\n<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>La clause SAMPLE de l&rsquo;ordre SELECT permet de r\u00e9aliser un \u00e9chantillonnage al\u00e9atoire des donn\u00e9es d&rsquo;une table. Le nombre de lignes<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"colormag_page_container_layout":"default_layout","colormag_page_sidebar_layout":"default_layout","footnotes":""},"categories":[6,14],"tags":[],"class_list":["post-242","post","type-post","status-publish","format-standard","hentry","category-oracle","category-statistique"],"_links":{"self":[{"href":"https:\/\/blog.tiran.stream\/index.php?rest_route=\/wp\/v2\/posts\/242","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.tiran.stream\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.tiran.stream\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.tiran.stream\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.tiran.stream\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=242"}],"version-history":[{"count":0,"href":"https:\/\/blog.tiran.stream\/index.php?rest_route=\/wp\/v2\/posts\/242\/revisions"}],"wp:attachment":[{"href":"https:\/\/blog.tiran.stream\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=242"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.tiran.stream\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=242"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.tiran.stream\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=242"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}