/** ctor for partial projection */
public Projection(Schema s, String projection) throws ParseException {
String[] colnames = projection.trim().split(Schema.COLUMN_DELIMITER);
for (int nx = 0; nx < colnames.length; nx++) {
colnames[nx] = colnames[nx].trim();
}
mKeys = new HashMap<Schema.ColumnSchema, HashSet<String>>();
mProjection = s.getProjectionSchema(colnames, mKeys);
mNumColumns = colnames.length;
mProjStr = projection;
mSchema = toSchema(projection);
}
