sql - How do I update just retrieved records without issuing an additional query? -

i have following piece of code:

string sql = "select * users email = " + email; prestat = dbconnection.preparestatement(sql); rs = prestat.executequery(); boolean isempty = !rs.first(); if (isempty) {   // special marker nonexistent user   return "$null"; } else if (password.equals(rs.getstring(2))) {   string uuid = uuid.randomuuid().tostring();   // here want insert uuid database }    

considering have searched database, i'm wondering if there way can row number/position,and use update uuid column, hence preventing db search.

it's not clear trying here, , doesn't seem understand goes on. example, when using prepared statement, 1 doesn't feed 2 concatenated strings, instead does:

preparedstatement stmt =         conn.preparestatement("select * foo bar = ?"); stmt.setstring(1, "hello world!"); 

then, if want avoid double search, can assume optimistic point of view:

update users set uuid = ? email = ? , password = ? 

ensure email unique, way. also, maybe it, don't save plaintext passwords in db. use cryptographic hashes instead, , salt them.

since specify backend apache derby, maybe this guide can solve problem (it's 100% java not portable because of different backends may not implement of required features). basically, pass 2 flags when preparing statement:

statement stmt = con.createstatement(     resultset.type_forward_only,      resultset.concur_updatable); resultset res = stmt.executequery("select * users email = ?"); 

and have resultset backed updateable cursor, can call:

res.updatestring("uuid", uuid); res.updaterow(); 

i think may avoid additional search, didn't test , cannot if there's real performance gain. sounds premature optimization, though.