用SELECT CASE創建函數

Question

我想用2個參數創建一個函數。這是我的SELECT聲明：

SELECT CASE 
    WHEN duration <= 10000000 THEN '00-01 sec' 
      WHEN duration <= 40000000 THEN '01-04 sec' 
      WHEN duration <= 100000000 THEN '04-10 sec' 
      WHEN duration <= 300000000 THEN '10-30 sec' 
      WHEN duration <= 600000000 THEN '30-60 sec' 
      ELSE 'more than 60 sec' END AS "Kategorien", 
    COUNT(*) AS Requestcounter 
FROM tablename 
WHERE starttime BETWEEN '2016-03-01 00:00:00' AND '2016-03-08 14:00:00' 
GROUP BY 
    (CASE WHEN duration <= 10000000 THEN '00-01 sec' 
    WHEN duration <= 40000000 THEN '01-04 sec' 
    ELSE 'more than 60 sec' END); 

結果：

Kategorien | requestcounter 
------------+---------------- 
00-01 sec |   2073 
01-04 sec |    2 
(2 rows) 

我想從我的函數這一結果。但我得到的錯誤：

query has no destination for result data

這是我的函數：

CREATE OR REPLACE FUNCTION requestcounter(mindate timestamptz,maxdate timestamptz) 
RETURNS SETOF integer AS $$ 

BEGIN 
SELECT CASE WHEN duration <= 10000000 THEN '00-01 sec' 
      WHEN duration <= 40000000 THEN '01-04 sec' 
      ELSE 'more than 60 sec' END AS "Kategorien", 
COUNT(*) AS Requestcounter from tablename where starttime BETWEEN mindate and maxdate 
GROUP BY 
    (CASE WHEN duration <= 10000000 THEN '00-01 sec' 
     WHEN duration <= 40000000 THEN '01-04 sec' 
     ELSE 'more than 60 sec' END); 
Return; 
END; 
$$ LANGUAGE plpgsql; 

我知道RETURNS SETOF integer是不對的，但我不知道如何得到這個工作？

Answer 1

@Travis已經規定，你需要RETURN QUERY實際上從plpgsql function返回查詢結果。

但是，您並不需要plpgsql作爲簡單的SELECT。改爲使用plain SQL function。您需要定義還提供了像@Travis返回類型無論哪種方式，最好使用RETURNS TABLE，但實際上返回的數據類型必須精確匹配：

CREATE OR REPLACE FUNCTION requestcounter(_mindate timestamptz, _maxdate timestamptz) 
    RETURNS TABLE (kategorien text, requestcounter int) AS 
$func$ 
SELECT CASE WHEN duration <= 10000000 THEN '00-01 sec'::text 
      WHEN duration <= 40000000 THEN '01-04 sec' 
      -- more cases ... 
      ELSE 'more than 60 sec' END -- AS kategorien -- not visible outside function 
    , count(*)::int      -- AS requestcounter 
FROM tablename 
WHERE starttime BETWEEN _mindate AND _maxdate 
GROUP BY 1        -- simpler with positional reference 
ORDER BY 1        -- see below 
$func$ LANGUAGE sql;     -- never quote the language name 

• count()回報bigint。如果你定義返回列requestcounter爲int，你要投：count(*)::int（或返回BIGINT開始。）

• 在一個SQL函數可以使用普通SELECT返回行。

• 避免參數和列名稱之間的命名衝突。一個常見的慣例是像我一樣前綴參數。

• GROUP BY中的位置參考是SELECT列表中長表達式的非常方便的語法快捷方式。這也確保GROUP BY項目匹配SELECT項目（這是而不是您的第一個查詢中的情況）。

• 您可能想要添加ORDER BY 1或者您獲得任意訂單。您的演示text值發生按正確順序排序。

電話：

SELECT * FROM requestcounter('2015-01-01 00:00+01', '2015-03-01 00:00+01') 

Answer 2

我想你想要返回一個表格，而不是SETOF INTEGER。

像這樣：

CREATE OR REPLACE FUNCTION requestcounter (mindate timestamptz, maxdate timestamptz) RETURNS TABLE (
    Kategorien text, 
    requestcounter int 
) AS 
$BODY$ 
BEGIN 
    RETURN QUERY 
    SELECT CASE WHEN duration <= 10000000 THEN '00-01 sec' 
       WHEN duration <= 40000000 THEN '01-04 sec' 
       ELSE 'more than 60 sec' END AS "Kategorien", 
    COUNT(*) AS Requestcounter from tablename where starttime BETWEEN mindate and maxdate GROUP BY 
    (CASE WHEN duration <= 10000000 THEN '00-01 sec' 
    WHEN duration <= 40000000 THEN '01-04 sec' 
    ELSE 'more than 60 sec' END); 
END 
$BODY$ 
LANGUAGE 'plpgsql'; 

我覺得你寫的功能正在運行無處選擇查詢發送輸出，那麼它返回一個空的整數集。 （這就是爲什麼你得到這個錯誤。）