Finding UnMatched Users from a Table - mysql

Question

I have an array of usernames as users:[Test1,Test2].I have to loop through this array and should find the unmatched usernames from table b.I have written the query as below:
def usersArray = []
def find
params.users.each{
find= sql.rows("select distinct name from table a,table b where a.id=b.id and b.name!=:n",[n:it])
if(find.size >0)
{
def usList = ["nm":find]
usersArray.push(usList);
}
}
From the above solution in my result i see both Test 1 and Test 2 even though they match.How should i change the query to display only the unmatched users?

Answer 1

Another way - count the existing rows which match the parameter name, then push those that have zero (forgive the bad syntax):
....
numberFound = sql.rows("select count(*)from table a where a.name=:n",[n:it])
if(numberFound = 0)
{
def usList = ["nm":find]
usersArray.push(usList);
}
...

Answer 2

Here is an example of how you might go about solving this problem. This assumes you have a domain class called User with a property called name which you want to match on.
// given a list of user names
​List users = ['Test1', 'Test2', 'Test3', 'Test4']
// find all the users that match those names, and collect the matched names into a List
List matched = User.findAll("from User as u where u.name in (:names)", [names: users]).collect { it.name }
// remove the matched names from the user list and arrive at an 'unmatched' names list
List unmatched = users.minus(matched)​​
This was written off the top of my head so please forgive any typos or other random assumptions.
UPDATED
Since you seem set on using SQL you might be able to do something like this instead
List users = ['Test1', 'Test2', 'Test3', 'Test4']
List placeholders = []
users.each { placeholders << '?' }
String select = "select distinct name from table a,table b where a.id=b.id and b.name in (${placeholders.join(',')})"
List matched = sql.rows(select, users)
List unmatched = users.minus(matched)​​