Below is the typical MERGE statement for SCD Type 2:<\/p>\n\n\n\n
insert into dest (a, b)\nselect a, b\nfrom\n(\n merge dest as target\n using src as source\n on source.a = target.a\n when not matched by target\n then insert (a,b) values(a,b)\n when matched\n then update set target.a = source.a, target.b = source.b\n output $Action as my_action\n) mrg\nwhere mrg.my_action = 'UPDATE'\n;<\/code><\/pre>\n\n\n\nSince a MERGE statement cannot update more than one match at a time, in scenarios which the source contains historical data that for each matching key (per ON statament) may need more than 1 action in a single merge statement run (e.g. one INSERT and multiple UPDATEs), above statement will not work properly.<\/p>\n\n\n\n
As a work around you can rank the source for multiple singular actions and put merge statement in a loop. Then every INSERT\/UPDATE action will run correctly per each MERGE run<\/p>\n\n\n\n
select a,b, rownumber() over(partition by a order by b) as rank\ninto #src\nfrom src\n\ndeclare @counter int = 1\ndeclare @max_counter int = (select max(rank) from #src)\n\nwhile @counter <= @max_counter\nbegin\n insert into dest (a, b)\n select a, b\n from\n (\n merge dest as target\n using (select a,b, from #src where rank = @counter)<\/strong> as source\n on source.a = target.a\n when not matched by target\n then insert (a,b) values(a,b)\n when matched\n then update set target.a = source.a, target.b = source.b\n output $Action as my_action\n ) mrg\n where mrg.my_action = 'UPDATE'\n ;\n set @counter = @counter + 1\nend<\/code><\/pre>\n\n\n\nNote the bold snippet in above is replaced with the previous “src”.<\/p>\n","protected":false},"excerpt":{"rendered":"
Below is the typical MERGE statement for SCD Type 2: Since a MERGE statement cannot update more than one match at a time, in scenarios which the source contains historical data that for each matching key (per ON statament) may need more than 1 action in a single merge statement run (e.g. one INSERT and … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2],"tags":[40,38,39,9],"_links":{"self":[{"href":"https:\/\/data-engineer.net\/index.php?rest_route=\/wp\/v2\/posts\/109"}],"collection":[{"href":"https:\/\/data-engineer.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/data-engineer.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/data-engineer.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/data-engineer.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=109"}],"version-history":[{"count":1,"href":"https:\/\/data-engineer.net\/index.php?rest_route=\/wp\/v2\/posts\/109\/revisions"}],"predecessor-version":[{"id":110,"href":"https:\/\/data-engineer.net\/index.php?rest_route=\/wp\/v2\/posts\/109\/revisions\/110"}],"wp:attachment":[{"href":"https:\/\/data-engineer.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=109"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/data-engineer.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=109"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/data-engineer.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=109"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}