DB2 char()函數引發全表掃描

解決方法是情願多幾回訪問數據庫，增長　Where 條件　縮小檢索範圍，不要用鏈接

原代碼：

List l = new ArrayList();  
StringBuffer sql = new StringBuffer(); 

sql.append("select log.LOGID,log.LASID,customerinfo.REALNAME,customer.IDTYPE,
            char(date(log.OPERATEDATE))||' '||char(time(log.OPERATEDATE)),log.OPERATETYPE,");  
sql.append("log.OPERATECODE,log.PRINTSTATE,log.FIRSTPRINTDATE,log.LASTPRINTDATE,log.LASTPRINTCODE,"); 
sql.append("log.EMAILSTATE,log.FIRSTEMAILDATE,log.LASTEMAILDATE,log.LASTEMAILCODE,log.PRINTID,"); 
sql.append("log.EMAILID,log.FLAG,customer.IDNO,customerinfo.SEX,customer.email,customer.mobile 
            from 日誌表　as log,　客戶表　as customer, 客戶詳情表 as customerinfo 
            
where log.LASID = char(customer.CUSTOMERID) 
and char(customer.CUSTOMERID)= char(customerinfo.CUSTOMERID)");

中　Where  條件　用到了　char()　函數，原來　DB2 中 where 條件中 引用函數會引發全表掃描，邏輯沒有什麼錯，就是線程卡在這裏。

修改： 分兩部分 先將 顧客ID搜出來，再去搜日誌

  1.先將 顧客ID搜出來

select customer.CUSTOMERID from 客戶表 as customer, 客戶詳情表 as customerinfo 
where customer.CUSTOMERID= customerinfo.CUSTOMERID for read only with ur

  2.再去搜日誌

StringBuffer sql = new StringBuffer(); 

sql.append("select log.LOGID,log.LASID,customerinfo.REALNAME,customer.IDTYPE, 
            char(date(log.OPERATEDATE))||' '||char(time(log.OPERATEDATE)),log.OPERATETYPE,"); 
sql.append("log.OPERATECODE,log.PRINTSTATE,log.FIRSTPRINTDATE,log.LASTPRINTDATE,log.LASTPRINTCODE,"); 
sql.append("log.EMAILSTATE,log.FIRSTEMAILDATE,log.LASTEMAILDATE,log.LASTEMAILCODE,log.PRINTID,");  
sql.append("log.EMAILID,log.FLAG,customer.IDNO,customerinfo.SEX,customer.email,customer.mobile 
            from 日誌表 as log, 客戶表 as customer,客戶詳情表 as customerinfo 
            
where log.LASID in ("); 	
for(Object CustomerId : CustomerIds){
    sql.append("'"+CustomerId.toString()+"',"); 
}
sql.deleteCharAt(sql.lastIndexOf(","));
sql.append(") AND for read only with ur");

記得加上 " for read only with ur "