mysql的SQL_CALC_FOUND_ROWS在postgresql中是否有類似的函數？

大家都用mysql知道：mysql的SQL_CALC_FOUND_ROWS在postgresql中是否有類似的函數？

SELECT SQL_CALC_FOUND_ROWS ..... FROM table WHERE ... LIMIT 5, 10;

，右運行此之後：

SELECT FOUND_ROWS();

我如何做到這一點的postrgesql？到目前爲止，我發現只有我必須發送查詢兩次的方法...

來源

2010-07-30 helle

不，沒有（至少not as of July 2007）。恐怕你不得不訴諸：

BEGIN ISOLATION LEVEL SERIALIZABLE; 

SELECT id, username, title, date FROM posts ORDER BY date DESC LIMIT 20; 
SELECT count(id, username, title, date) AS total FROM posts; 

END;

的isolation level需要爲SERIALIZABLE，以確保查詢沒有看到SELECT語句之間的併發更新。

但是，您擁有的另一選項是使用觸發器對行進行計數，因爲它們是INSERT ed或DELETE d。假設你有如下表：

CREATE TABLE posts (
    id  SERIAL PRIMARY KEY, 
    poster TEXT, 
    title TEXT, 
    time TIMESTAMPTZ DEFAULT now() 
); 

INSERT INTO posts (poster, title) VALUES ('Alice', 'Post 1'); 
INSERT INTO posts (poster, title) VALUES ('Bob',  'Post 2'); 
INSERT INTO posts (poster, title) VALUES ('Charlie', 'Post 3');

然後，執行以下步驟來創建一個名爲POST_COUNT表包含posts行數的運行計數：

-- Don't let any new posts be added while we're setting up the counter. 
BEGIN; 
LOCK TABLE posts; 

-- Create and initialize our post_count table. 
SELECT count(*) INTO TABLE post_count FROM posts; 

-- Create the trigger function. 
CREATE FUNCTION post_added_or_removed() RETURNS TRIGGER AS $$ 
    BEGIN 
     IF TG_OP = 'DELETE' THEN 
      UPDATE post_count SET count = count - 1; 
     ELSIF TG_OP = 'INSERT' THEN 
      UPDATE post_count SET count = count + 1; 
     END IF; 
     RETURN NULL; 
    END; 
$$ LANGUAGE plpgsql; 

-- Call the trigger function any time a row is inserted. 
CREATE TRIGGER post_added_or_removed_tgr 
    AFTER INSERT OR DELETE 
    ON posts 
    FOR EACH ROW 
    EXECUTE PROCEDURE post_added_or_removed(); 

COMMIT;

注意這個保持運行計數爲，全部爲，行數爲posts。爲了保持一定行的運行計數，你必須調整它：

SELECT count(*) INTO TABLE post_count FROM posts WHERE poster <> 'Bob'; 

CREATE FUNCTION post_added_or_removed() RETURNS TRIGGER AS $$ 
    BEGIN 
     -- The IF statements are nested because OR does not short circuit. 
     IF TG_OP = 'DELETE' THEN 
      IF OLD.poster <> 'Bob' THEN 
       UPDATE post_count SET count = count - 1; 
      END IF; 
     ELSIF TG_OP = 'INSERT' THEN 
      IF NEW.poster <> 'Bob' THEN 
       UPDATE post_count SET count = count + 1; 
      END IF; 
     END IF; 
     RETURN NULL; 
    END; 
$$ LANGUAGE plpgsql;

來源

2010-07-30 16:17:07

好，感謝您的！ – helle 2010-07-31 19:23:30

不，PostgreSQL並不試圖計算所有相關結果時，你只需要10個結果。您需要一個單獨的COUNT來計算所有結果。

來源

2010-07-30 16:52:15

有一個簡單的方法，但請記住，以下COUNT（*）匯聚功能將應用於所有行回來後，在那裏和限制之前/偏移量（可能是costy）

選擇 ID，「計數」（*）OVER（）AS CNT FROM 對象 WHERE ID> 2 OFFSET 50 LIMIT 5

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2012-12-20 15:23:36 Karisters

mysql的SQL_CALC_FOUND_ROWS在postgresql中是否有類似的函數？

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