{"id":808,"date":"2009-08-14T07:42:00","date_gmt":"2009-08-14T07:42:00","guid":{"rendered":"\/blogs\/paul\/post\/How-are-auto-created-column-statistics-names-generated.aspx"},"modified":"2009-08-14T07:42:00","modified_gmt":"2009-08-14T07:42:00","slug":"how-are-auto-created-column-statistics-names-generated","status":"publish","type":"post","link":"https:\/\/www.sqlskills.com\/blogs\/paul\/how-are-auto-created-column-statistics-names-generated\/","title":{"rendered":"How are auto-created column statistics names generated?"},"content":{"rendered":"

\nThis is a question that came up at the Cleveland SQL Server User Group last night. An attendee had a wager with his colleagues about how the names of auto-created column-level stats are generated.<\/font>\n<\/p>\n

\nLet's find out. I'm going to create a table without any indexes and then do some queries.<\/font>\n<\/p>\n

\n

\n\tUSE master;
\n\tGO
\n\tCREATE DATABASE StatsTest;
\n\tGO
\n\tUSE StatsTest;
\n\tGO<\/font>\n\t<\/p>\n

\n\tEXEC sp_dboption 'StatsTest', 'auto create statistics', 'on';
\n\tGO<\/font>\n\t<\/p>\n

\n\tCREATE TABLE t1 (c1 INT, c2 INT, c3 INT);
\n\tGO
\n\tINSERT INTO t1 VALUES (1, 1, 1);
\n\tINSERT INTO t1 VALUES (1, 1, 2);
\n\tINSERT INTO t1 VALUES (1, 1, 3);
\n\tGO<\/font>\n\t<\/p>\n<\/blockquote>\n

\nNow I'll do a little query. My database has AUTO_CREATE_STATISTICS turned out, so the query optimizer recognizes that it could use a statistic to potentially help choose a more efficient query plan more quickly – so it generates it.<\/font>\n<\/p>\n

\n

\n\tSELECT * FROM t1 WHERE c3 < 2;
\n\tGO<\/font>\n\t<\/p>\n

\n\tSELECT [object_id], [name] FROM sys.stats
\n\tWHERE [object_id] = OBJECT_ID ('t1');
\n\tGO<\/font>\n\t<\/p>\n

\n\tobject_id   name
\n\t———– ————————–
\n\t2073058421  _WA_Sys_00000003_7B905C75<\/font>
\n\t<\/font>\n\t<\/p>\n<\/blockquote>\n

\nI've got an automatically created statistic – but what does the name mean? Well, the 7B905C75<\/strong><\/font> is the hex equivalent of the table's object ID. The Sys<\/strong><\/font> is because it was automatically created. The WA<\/strong><\/font> is because the SQL team is based in Washington State in the US (I'm absolutely serious!). The 00000003<\/strong><\/font> is because the statistic is on column ID 3 of the table. I can prove this last one by doing a select on column ID 1 and checking the new statistic that is created.<\/font>\n<\/p>\n

\n

\n\tSELECT * FROM t1 WHERE c1 < 2;
\n\tGO<\/font>\n\t<\/p>\n

\n\tSELECT [object_id], [name] FROM sys.stats
\n\tWHERE [object_id] = OBJECT_ID ('t1');
\n\tGO<\/font>\n\t<\/p>\n

\n\tobject_id   name
\n\t———– ————————–
\n\t2073058421  _WA_Sys_00000003_7B905C75
\n\t2073058421  _WA_Sys_00000001_7B905C75<\/font>\n\t<\/p>\n<\/blockquote>\n

\nThe new statistic has the exact same name as the previous one, but the first number is now 00000001<\/strong><\/font> – clearly matching the column ID of the column I queried.<\/font>\n<\/p>\n

\nSo there you go – wager settled!<\/font><\/p>\n","protected":false},"excerpt":{"rendered":"

This is a question that came up at the Cleveland SQL Server User Group last night. An attendee had a wager with his colleagues about how the names of auto-created column-level stats are generated. Let's find out. I'm going to create a table without any indexes and then do some queries. USE master; GO CREATE […]<\/p>\n","protected":false},"author":5,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[90],"tags":[],"class_list":["post-808","post","type-post","status-publish","format-standard","hentry","category-statistics"],"yoast_head":"\nHow are auto-created column statistics names generated? - Paul S. 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