sql server 2008 - SQL Basic Concurrency -
insert t1 (xfield) select 7 xfield (select count(*) t1) = 0 basically, if million users run @ same time, there ever end being more 1 row in t1? thread a: select count(*) t1: 0 thread b: select count(*) t1: 0 thread a: insert t1... thread b: insert t1... or guaranteed never happen, because it's 1 statement? if isn't safe, this? table t2 (gonorth , gosouth must never both 1): id gonorth gosouth 1 0 0 then happens: user a: update t2 set gonorth = 1 gosouth = 0 user b: update t2 set gosouth = 1 gonorth = 0 thread a: find rows gosouth = 0 thread b: find rows gonorth = 0 thread a: found row gosouth = 0 thread b: found row gonorth = 0 thread a: setting gonorth = 1 located row thread b: setting gosouth = 1 located row and result: id gonorth gosouth 1 1 1 what rules can happen @ same time , can't? my database engine "microsoft sql server 2008 r2 (sp2)". no. it's written single statement, , ...