Sql Firebird在where和order by条款上的履行

我有一个查询，基本上可以找到特定日期范围内特定项目的最后成本

select first 1 lastcost from stock 
where itemid = :itemid and date > :startdate and date < :enddate 
order by date desc

这几天我没有机会接触到firebird，所以我自己也没试过

提前谢谢

问候,

---

雷诺第

不，循环迭代总是比传统的

SELECT

语句慢

---

如果可以，则“”将使用索引；查看在索引中添加'itemid'是否有帮助

您可能需要在日期上同时使用升序和降序索引

此外，您还可以使用“”语法：

---

Firebird使用索引（如果适用于>，=，

while (endate > startdate) do
begin
  var_year = extract(year from :endate);
  var_month = extract(month from :endate);
  select first 1 lastcost from stock 
  where itemid = :itemid and year=:var_year and month=:var_month
  order by date desc
  enddate = dateadd (-1 month to enddate);
end

select first 1 lastcost from stock 
where itemid = :itemid and date between :startdate and :enddate 
order by date desc

SQL> show table stock2;
ITEMID                          INTEGER Not Null
STOCKDATE                       TIMESTAMP Not Null
LASTCOST                        DOUBLE PRECISION Nullable

SQL> select extract(year from stockdate),
CON>        extract(month from stockdate), count(*)
CON>   from stock2
CON>  group by 1, 2
CON>  order by 1, 2;

EXTRACT EXTRACT        COUNT
======= ======= ============
   2012       1       706473
   2012       2       628924
   2012       3       670038
   2012       4       649411
   2012       5       671512
   2012       6       648878
   2012       7       671182
   2012       8       671212
   2012       9       649312
   2012      10       671881
   2012      11       648815
   2012      12       671579

SQL> set plan on;
SQL>
SQL> select first 1 lastcost
CON>   from stock2
CON>  where itemid = 127
CON>    and stockdate > '2012-01-15'
CON>    and stockdate < '2012-03-27'
CON> order by stockdate desc;

PLAN SORT ((STOCK2 INDEX (IDX_STOCK2IDDATE)))

               LASTCOST
=======================
      149.7170031070709

SQL>

create index idx_stock2id on stock2 (itemid);
create index idx_stock2iddate on stock2 (itemid, stockdate);