使用in（select ...）子句進行查詢優化

Question

我在Windows上使用Firebird WI-V3.0.4.33054。

我在優化此查詢時遇到問題，該查詢使用帶有select的in子句：

update CADPC p set p.STA = 'L'
where p.COD in (select distinct CODPC from CADPCI_Rec where IDNfr = 27)
and not exists (select * from CADPCI where CODPC = p.COD)

此查詢的計划是（並且明顯的問題是P NATURAL部分）：

PLAN SORT (CADPCI_REC INDEX (PK_CADPCI_REC))
PLAN (CADPCI INDEX (FK_CADPCI_CODPC))
PLAN (P NATURAL)

Select Expression
    -> Filter
        -> Unique Sort (record length: 36, key length: 8)
            -> Filter
                -> Table "CADPCI_REC" Access By ID
                    -> Bitmap
                        -> Index "PK_CADPCI_REC" Range Scan (partial match: 1/3)
Select Expression
    -> Filter
        -> Table "CADPCI" Access By ID
            -> Bitmap
                -> Index "FK_CADPCI_CODPC" Range Scan (full match)
Select Expression
    -> Filter
        -> Table "CADPC" as "P" Full Scan

另一方面，如果我手動運行select distinct ，則復制結果並粘貼到查詢中，如下所示：

update CADPC p set p.STA = 'L'
where p.COD in (5699, 5877, 5985)
and not exists (select * from CADPCI where CODPC = p.COD)

現在，優化器為P表選擇合理的計划，查詢運行得非常快：

PLAN (CADPCI INDEX (FK_CADPCI_CODPC))
PLAN (P INDEX (PK_CADPC, PK_CADPC, PK_CADPC))

Select Expression
    -> Filter
        -> Table "CADPCI" Access By ID
            -> Bitmap
                -> Index "FK_CADPCI_CODPC" Range Scan (full match)
Select Expression
    -> Filter
        -> Table "CADPC" as "P" Access By ID
            -> Bitmap Or
                -> Bitmap Or
                    -> Bitmap
                        -> Index "PK_CADPC" Unique Scan
                    -> Bitmap
                        -> Index "PK_CADPC" Unique Scan
                -> Bitmap
                    -> Index "PK_CADPC" Unique Scan

我也試過在兩種情況下都存在，但結果是一樣的：每個行重新評估子查詢。

update CADPC p set p.STA = 'L'
where exists (select * from CADPCI_Rec where IDNfr = 27 and CODPC = p.COD)
and not exists (select * from CADPCI where CODPC = p.COD)

計划：

PLAN (CADPCI_REC INDEX (PK_CADPCI_REC))
PLAN (CADPCI INDEX (FK_CADPCI_CODPC))
PLAN (P NATURAL)

Select Expression
    -> Filter
        -> Table "CADPCI_REC" Access By ID
            -> Bitmap
                -> Index "PK_CADPCI_REC" Range Scan (partial match: 1/3)
Select Expression
    -> Filter
        -> Table "CADPCI" Access By ID
            -> Bitmap
                -> Index "FK_CADPCI_CODPC" Range Scan (full match)
Select Expression
    -> Filter
        -> Table "CADPC" as "P" Full Scan

所以，問題是：當in子句包含一個select（通常只有幾個記錄）時，我能以某種方式讓引擎選擇索引計划嗎？

Answer 1

嘗試使用exists for both：

update CADPC p
    set p.STA = 'L'
    where exists (select 1 from CADPCI_Rec where r.IDNfr = 27 and p.COD = r.CODPC) and
         not exists (select 1 from CADPCI c2 where c2.CODPC = p.COD);

特別是，您需要CADPCI_Rec(CODPC, IDNfr)的索引。

Answer 2

你可以試試EXECUTE BLOCK和“反轉控制”

• https://firebirdsql.org/file/documentation/reference_manuals/fblangref25-en/html/fblangref25-dml-execblock.html
• https://firebirdsql.org/file/documentation/reference_manuals/fblangref25-en/html/fblangref25-psql-coding.html#fblangref25-psql-forselect

基本上發布匿名ad hoc存儲過程

EXECUTE BLOCK AS
  declare id INTEGER;
BEGIN
  for select distinct t1.CODPC from CADPCI_Rec t1 
    left join CADPCI t2 on where t2.CODPC = t1.CODPC
  where t2.CODPC is NULL and t1.IDNfr = 27
  into :id
  do 
    update CADPC p set p.STA = 'L' where p.COD = :ID and p.STA <> 'L';
END

---

您也可以使用全球臨時表（GTT）

• https://firebirdsql.org/refdocs/langrefupd21-ddl-table.html

然后在實際刪除之前創建ID列表。

數據庫准備（創建無體表）：

CREATE GLOBAL TEMPORARY TABLE CADPC_mark_IDs
   ( ID integer )
ON COMMIT DELETE ROWS

然后命令就像

insert into CADPC_mark_IDs(ID)
select distinct t1.CODPC from CADPCI_Rec t1 
   left join CADPCI t2 on where t2.CODPC = t1.CODPC
where t2.CODPC is NULL and t1.IDNfr = 27

然后

update CADPC p set p.STA = 'L'
where p.COD in (select * from CADPC_mark_IDs) and p.STA <> 'L'

然后

commit; -- clear the in-memory table for next uses

---

像Mark建議的那樣，在你將“不存在的地方”轉換成“左連接”（已經在上面完成，希望是正確的）后，將使用MERGE 。

• https://firebirdsql.org/refdocs/langrefupd21-merge.html

一切順利

merge into CADPC p
  using (
    select distinct t1.CODPC as id from CADPCI_Rec t1 
      left join CADPCI t2 on where t2.CODPC = t1.CODPC
    where t2.CODPC is NULL and t1.IDNfr = 27
  ) t
on (t.id = p.COD) and (p.STA <> 'L')
when matched then update set p.STA = 'L'