12c中的with與函數的結合
在sql語句中用到函數是會發生sql和pl/sql引擎的上下問切換，在12C版本中可以用with來避免這個切換，來提升性能
如下
WITH FUNCTION full_name (fname_in IN VARCHAR2, lname_in IN VARCHAR2)
RETURN VARCHAR2
IS
BEGIN
RETURN fname_in || ' ' || lname_in;
END;
SELECT full_name(first_name, last_name)
FROM employees
利用表函數和遊標的結合來將複雜的數據結構傳遞給JDBC
例如把一個嵌套錶轉換爲遊標形式就可以如下操作,
CREATE TYPE pet_t IS OBJECT (
NAME VARCHAR2 (60)
, breed VARCHAR2 (100)
, dob DATE
);
/
CREATE TYPE pet_nt IS TABLE OF pet_t;
/
CREATE OR REPLACE FUNCTION pet_family (dad_in IN pet_t, mom_in IN pet_t)
RETURN pet_nt
IS
l_count PLS_INTEGER;
retval pet_nt := pet_nt ();
BEGIN
retval.EXTEND;
retval (retval.LAST) := dad_in;
retval.EXTEND;
retval (retval.LAST) := mom_in;
IF mom_in.breed = 'RABBIT'
THEN
l_count := 12;
ELSIF mom_in.breed = 'DOG'
THEN
l_count := 4;
ELSIF mom_in.breed = 'KANGAROO'
THEN
l_count := 1;
END IF;
FOR indx IN 1 .. l_count
LOOP
retval.EXTEND;
retval (retval.LAST) :=
pet_t ('BABY' || indx, mom_in.breed, SYSDATE - indx);
END LOOP;
RETURN retval;
END pet_family;
/
REM Call the table function within a SELECT staement.
SELECT pets.NAME, pets.dob
FROM TABLE (pet_family (pet_t ('Hoppy', 'RABBIT', SYSDATE)
, pet_t ('Hippy', 'RABBIT', SYSDATE)
)
) pets;
REM Place the same query inside a PL/SQL function returning a cursor variable.
CREATE OR REPLACE FUNCTION pet_family_cv
RETURN sys_refcursor
IS
retval sys_refcursor;
BEGIN
OPEN retval FOR
SELECT *
FROM TABLE (pet_family (pet_t ('Hoppy', 'RABBIT', SYSDATE)
, pet_t ('Hippy', 'RABBIT', SYSDATE)
)
);
RETURN retval;
END pet_family_cv;
/
數據流函數
在做ETL轉換的時候，把一行數據轉換成兩行，或者把兩行數據轉換成一行。
下面的一個原始股票信息stocktable中的一行數據拆分到另一個表中tickertable，
建表信息如下：
--這個表含股票代碼，交易日期，開盤價，收盤價，這幾個要素都在一行中
CREATE TABLE stocktable (
ticker VARCHAR2(20),
trade_date DATE,
open_price NUMBER,
close_price NUMBER
)
/
--這個表是開盤價格和收盤價格各佔一行
CREATE TABLE tickertable
(
ticker VARCHAR2(20),
pricedate DATE,
pricetype VARCHAR2(1),
price NUMBER
)
/
傳統方式：
- pl/sql
FOR rec IN (SELECT *
FROM stocktable)
LOOP
INSERT INTO tickertable
(ticker, pricetype, price)
VALUES (rec.ticker, 'O', rec.open_price);
INSERT INTO tickertable
(ticker, pricetype, price)
VALUES (rec.ticker, 'C', rec.close_price);
END LOOP;
- 純sql解決方案
insert ALL
INTO tickertable
(ticker,
pricetype,
price)
VALUES
(ticker,
'O',
open_price)
INTO tickertable
(ticker,
pricetype,
price)
VALUES
(ticker,
'C',
close_price)
select ticker,
trade_date,
open_price,
close_price
FROM stocktable;
數據流函數解決方案
大致思路：
- 在schema中創建基於表stocktable的object對象，然後創建基於對象的嵌套表
CREATE TYPE tickertype AS OBJECT (
ticker VARCHAR2 (20)
, pricedate DATE
, pricetype VARCHAR2 (1)
, price NUMBER
);
/
CREATE TYPE tickertypeset AS TABLE OF tickertype;
/
- 創建基於表stocktable的ref cursor（遊標類型）
CREATE OR REPLACE PACKAGE refcur_pkg
IS
TYPE refcur_t IS REF CURSOR
RETURN stocktable%ROWTYPE;
END refcur_pkg;
/sql
- 編寫透視函數
CREATE OR REPLACE FUNCTION stockpivot (dataset refcur_pkg.refcur_t)
RETURN tickertypeset
IS
out_obj tickertype := tickertype (NULL, NULL, NULL, NULL);
TYPE dataset_tt IS TABLE OF stocktable%ROWTYPE
INDEX BY PLS_INTEGER;
l_dataset dataset_tt;
/* The nested table that will be returned. */
retval tickertypeset := tickertypeset ();
BEGIN
LOOP
/* Move N rows from cursor variable (SELECT) to local collection. */
FETCH dataset
BULK COLLECT INTO l_dataset LIMIT 100;
EXIT WHEN l_dataset.COUNT = 0;
/* Iterate through each row.... */
FOR l_row IN 1 .. l_dataset.COUNT
LOOP
/* START application specific logic.
This will vary depending on your transformation. */
/* Create open price object type and add to collection. */
out_obj.ticker := l_dataset (l_row).ticker;
out_obj.pricetype := 'O';
out_obj.price := l_dataset (l_row).open_price;
out_obj.pricedate := l_dataset (l_row).trade_date;
retval.EXTEND;
retval (retval.LAST) := out_obj;
/* Create close price object type and add to collection. */
out_obj.pricetype := 'C';
out_obj.price := l_dataset (l_row).close_price;
out_obj.pricedate := l_dataset (l_row).trade_date;
retval.EXTEND;
retval (retval.LAST) := out_obj;
END LOOP;
END LOOP;
CLOSE dataset;
RETURN retval;
END;
/
- 編寫插入sql語句
這個地方用到了遊標表達式和table函數
BEGIN
INSERT INTO tickertable
SELECT *
FROM TABLE (stockpivot (CURSOR (SELECT *
FROM stocktable)));
END;
/
管道函數
管道函數可以用在分頁當中，當用戶需要分頁的時候才正整執行查詢，而不是進入第一頁就執行全部查詢，這樣能提升性能，如下：
CREATE OR REPLACE FUNCTION stockpivot_pl (dataset refcur_pkg.refcur_t)
RETURN tickertypeset PIPELINED --此處加入管道聲明
IS
l_row_as_object tickertype := tickertype (NULL, NULL, NULL, NULL);
TYPE dataset_tt IS TABLE OF dataset%ROWTYPE
INDEX BY PLS_INTEGER;
l_dataset dataset_tt;
l_row PLS_INTEGER;
BEGIN
FETCH dataset
BULK COLLECT INTO l_dataset;
CLOSE dataset;
l_row := l_dataset.FIRST;
WHILE (l_row IS NOT NULL)
LOOP
-- first row
l_row_as_object.ticker := l_dataset (l_row).ticker;
l_row_as_object.pricetype := 'O';
l_row_as_object.price := l_dataset (l_row).open_price;
l_row_as_object.pricedate := l_dataset (l_row).trade_date;
--PIPE ROW 是關鍵
PIPE ROW (l_row_as_object);
-- second row
l_row_as_object.pricetype := 'C';
l_row_as_object.price := l_dataset (l_row).close_price;
--
PIPE ROW (l_row_as_object);
l_row := l_dataset.NEXT (l_row);
END LOOP;
RETURN; --注意，return沒有返回任何東西，執行單純的return即程序結束，返回上一級
END;
/
使用的時候這樣使用:
BEGIN
INSERT INTO tickertable
SELECT *
FROM TABLE (stockpivot_pl (CURSOR (SELECT *
FROM stocktable)))
WHERE ROWNUM < 10;
END;
確定性函數
確定性函數就是無論任何時候，傳入的參數是123，返回的總是456，跟數據庫的具體數據變化無關，對於一些自定義的字符串處理函數我們可以聲明下是確定函數,在return函數後面加上 DETERMINISTIC 即可。
CREATE OR REPLACE FUNCTION betwnstr (
string_in IN VARCHAR2
, start_in IN INTEGER
, end_in IN INTEGER
)
RETURN VARCHAR2 DETERMINISTIC
IS
BEGIN
DBMS_LOCK.sleep (.01);
RETURN (SUBSTR (string_in, start_in, end_in - start_in + 1));
END;
/