sql server - C# / SQL Efficiency Query -

i've got winforms application connects sql database , retrieves data, application needs check if data exists in sql database before performing action.

i've seen similar queries tend sql, i'd know of 2 options below, better in terms of overall performance. i've considered 2 approaches:

1.create 2 lists in c#, populate them , check if value first list exists in next list:

list<t> firstlist = new list<t>(); list<x> secondlist = new list<x>();  firstlist = firstlist.populate(); // sql stored procedure populate list secondlist = secondlist.populate(); // sql stored procedure populate list   foreach(var item in firstlist) {   if( (x => x.value == item.value) )   {      //do action   } } 

2.create list in c# , method executes stored procedure check if value passed parameter exists in sql database. once list populated iterate through , execute new method returning boolean value:

list<t> firstlist = new list<t>();  firstlist = firstlist.populate();  // sql stored procedure populate list  foreach(var item in firstlist) {   bool exists = false;   exists = firstlist.checkvalue(item.value);  // sql stored procedure check if value exists   if(exists)   {      //do action   } } 

i'm not sure whether it's better perform many sql queries , reduce memory usage or perform fewer queries , use memory. application run on small application server should have 32gb ram.

i'm open using technique if either of approaches aren't efficient.

i suggest more efficient run whole query on sql server. retrieving any data remote database , doing comparison locally never quicker doing comparison source of data held.

my suggestion write sproc comparison , returns rows exist in both databases.

possibly use like:

select     *     [server2name].[thedb].[theowner].[thetable] 

or have @ linked tables in sql server