選擇零發生的月度計數

我的問題是根據他們的肌酸年份和月份從數據庫中選擇記錄計數。我有這樣的MySQL查詢：選擇零發生的月度計數

SELECT year, m, month, COUNT(bans.ban_id) AS total 
FROM (
    SELECT year, m, month 
    FROM 
    (SELECT YEAR(CURDATE()) year UNION ALL SELECT YEAR(CURDATE())-1) years, 
    (
     SELECT 1 m, 'Jan' month 
     UNION ALL SELECT 2 m, 'Feb' month 
     UNION ALL SELECT 3 m, 'Mar' month 
     UNION ALL SELECT 4 m, 'Apr' month 
     UNION ALL SELECT 5 m, 'May' month 
     UNION ALL SELECT 6 m, 'Jun' month 
     UNION ALL SELECT 7 m, 'Jul' month 
     UNION ALL SELECT 8 m, 'Aug' month 
     UNION ALL SELECT 9 m, 'Sep' month 
     UNION ALL SELECT 10 m, 'Oct' month 
     UNION ALL SELECT 11 m, 'Nov' month 
     UNION ALL SELECT 12 m, 'Dec' month 
    ) months 
) ym 
LEFT JOIN bans 
    ON ym.year = YEAR(bans.ban_created_at) 
    AND ym.m = MONTH(bans.ban_created_at) 
WHERE 
    (year=YEAR(CURDATE()) AND m<=MONTH(CURDATE())) 
    OR 
    (year<YEAR(CURDATE()) AND m>MONTH(CURDATE())) 
    AND 
    (ban_banlist_id = 13) 
GROUP BY year, m

據工作幾乎是正常的，但 - 問題是，查詢返回只記錄有效的計數值 - 例如當月份沒有記錄時，不返回。請問你能幫幫我嗎？ :)

感謝，
TheKronnY

來源

2016-02-01 TheKronnY

的原因是，在右表中的狀態（禁令）是在WHERE子句，因此它的結果應用，用的效果，只有一個月出現次數會被選中。把它放在LEFT JOIN子句中的ON子句，像這樣：

SELECT year, m, month, COUNT(bans.ban_id) AS total 
FROM (
    SELECT year, m, month 
    FROM 
    (SELECT YEAR(CURDATE()) year UNION ALL SELECT YEAR(CURDATE())-1) years, 
    (
     SELECT 1 m, 'Jan' month 
     UNION ALL SELECT 2 m, 'Feb' month 
     UNION ALL SELECT 3 m, 'Mar' month 
     UNION ALL SELECT 4 m, 'Apr' month 
     UNION ALL SELECT 5 m, 'May' month 
     UNION ALL SELECT 6 m, 'Jun' month 
     UNION ALL SELECT 7 m, 'Jul' month 
     UNION ALL SELECT 8 m, 'Aug' month 
     UNION ALL SELECT 9 m, 'Sep' month 
     UNION ALL SELECT 10 m, 'Oct' month 
     UNION ALL SELECT 11 m, 'Nov' month 
     UNION ALL SELECT 12 m, 'Dec' month 
    ) months 
) ym 
LEFT JOIN bans 
    ON ym.year = YEAR(bans.ban_created_at) 
    AND ym.m = MONTH(bans.ban_created_at) 
    AND ban_banlist_id = 13 
WHERE 
    (year=YEAR(CURDATE()) AND m<=MONTH(CURDATE())) 
    OR 
    (year<YEAR(CURDATE()) AND m>MONTH(CURDATE())) 
GROUP BY year, m

來源

2016-02-01 08:47:24

它完美，非常感謝。 :)你能簡單解釋一下爲什麼？ – TheKronnY

如果你在左連接的右邊表格的where子句上添加一個條件（在這裏禁止），它只會選擇那些有禁止的行（這裏id = 13），所以最後你只會有id = 13的禁令的結果，如果沒有發生，則沒有任何結果。所以爲此，如果右表（禁止）存在條件，則將其置於ON子句中。 –

明白了！謝謝！ ^^ – TheKronnY

選擇零發生的月度計數

回答

相關問題