Executing multiple COUNT queries in Java - mysql

Question

I have a MySQL database (ver. 5.2 CE) and I have a table which I want to filter into a another table based on the WHERE conditions given by the user (this comes from an array list). I want to perform count query on this new table for a split chosen by the user. For example, COUNT(*) from TableName WHERE [userConditions like gender=male and gender=female, etc]. The user can give more than one WHERE conditions but the COUNT query will only take one condition at a time. Hence, I made my method (which performs this query) an array to return multiple queries based on the number of conditions chosen by the user and then execute each query in a for loop. However, this seems to give me compilation errors in 2 ways: i) the way I return a built string in a String[] method and ii) the way I execute the COUNT query. The code for these problems:
private String countQuery;
public SetupSubsamplePopulation(UserSelectedSplit split) {
this.split = split;
// connect to the database
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mysql?zeroDateTimeBehavior=convertToNull","root", "sharadha_1992");
String buildSelectQuery = buildSelectQueryForCode();
String getRowsFromTable = getNumberOfRows();
stmt = connection.createStatement();
rows = stmt.executeUpdate(buildSelectQuery);
ResultSet rs = stmt.executeQuery(getRowsFromTable);
for (int i=0; i<getCountOfWhereCondition().length; i++){
//where I get the executeQuery error
ResultSet rs1= stmt.execute(getCountOfWhereCondition());
while (rs1.next()){
rowsCount= rs.getRow();
rows_count++;
}
}
while (rs.next()) {
rows = rs.getRow();
rows_inserted++;
}
System.out.println(rows_inserted);
System.out.println(rows_count);
} catch (Exception e) {
e.printStackTrace();
}
}
The method which returns the array of COUNT queries:
public String[] getCountOfWhereCondition() {
countQuery="SELECT COUNT (*) FROM (SELECT * from mygrist_samples.subsample_population WHERE ";
for (int i = 0; i < split.getSplitConditions().size(); i++) {
String getCorrespondingCodeFromDatabase = split.getSplitConditions().get(i).getCode();
getCorrespondingCodeFromDatabase = getCorrespondingCodeFromDatabase.replaceAll("-", "_");
Enumerations enum1 = new Enumerations();
String getCorrespondingRelationshipOperator = enum1.getOperator(split.getSplitConditions().get(i).getRelationship());
countQuery+=getCorrespondingCodeFromDatabase + " " + getCorrespondingRelationshipOperator + " '" + split.getSplitConditions().get(i).getAnswer() + "'";
}
countQuery+=")";
System.out.println(countQuery);
//error which doesn't allow me to return a string
return countQuery;
}
Can someone please tell me how to implement this sensibly? Thank you very much.

Answer 1

I think you want conditional aggregation rather than a where:
select count(*)
from mygrist_samples.subsample_population
WHERE XXX
Is the same as:
select sum(case when XXX then 1 else 0 end) as cnt1
from mygrist_samples.subsample_population
Now you can add multiple conditions on one call:
select sum(case when XXX then 1 else 0 end) as cnt1,
sum(case when yyy then 1 else 0 end) as cnt1
from mygrist_samples.subsample_population