string concat problem

Denne string udskrives forkert:

sql = "SELECT * FROM ['" + db_table + "'] WHERE ";

for(int i=0; 0<count; i++)
{
sql = sql + ColumnName + " = '" + blabla + "'";

if(i+1<count)
  {
    sql = sql + " OR ";
  }
}

sql udskrives: SELECT * FROM [MyTable]id = 'blabla' OR ....

Altså WHERE mangler ?!?!?!?  Hvor hulen går det galt ??