通過MAX挑戰LEFT OUTER JOIN查詢分組

Question

我有以下兩個表：

BillingMatrixDefinition
    - id
    - amount

BillingMatrix
   - definition (FK to table above)
   - service_id (FK)
   - provider_id (FK)
   - amount (Decimal)

我需要獲取具有我指定的service_id和provider_id所有BillingMatrixDefinitions。 這是我當前擁有的SQL查詢：

select def.id, service_id, provider_id, 
 (case when matrix.amount is not null then matrix.amount else def.amount end) amount
    from billing_billingdefinition def 
        left outer join billing_billingmatrix matrix
        on matrix.definition_id=def.id 
    where (service_id = 25 or service_id is null)
      and (provider_id = 24 or provider_id is null)

這給了我以下結果：

id      service_id  provider_id   amount
1       25          24            200.00
1       NULL        24            300.00
2       NULL        24            800.00
3       NULL        NULL          750.00
5       NULL        NULL          450.00
6       NULL        NULL          750.00

但是，我需要得到每個ID的結算量，所以我只能得到一個項目/金額為每個id 。 在這種情況下，我想獲取service_id=24的項目，如果不存在，請在service_id=NULL 。

正確的查詢應該給我以下結果：

id      service_id  provider_id   amount
1       25          24            200.00
2       NULL        24            800.00
3       NULL        NULL          750.00
5       NULL        NULL          450.00
6       NULL        NULL          750.00

請注意，現在沒有1的重復條目，我使用已輸入service_id的行項目（如果存在，則使用該項目，否則使用NULL）。 什么是正確的查詢來做到這一點？

Answer 1

另一種方式：

SELECT 
    def.id                                              AS id, 
    COALESCE(matrix.service_id, matrix2.service_id)     AS service_id, 
    COALESCE(matrix.provider_id, matrix2.provider_id)   AS provider_id, 
    COALESCE(matrix.amount, matrix2.amount, def.amount) AS amount 
FROM 
        billing_billingdefinition AS def 
    LEFT JOIN 
        billing_billingmatrix AS matrix 
            ON  matrix.definition_id = def.id 
            AND matrix.service_id = 25 
            AND matrix.provider_id = 24 
    LEFT JOIN 
        billing_billingmatrix AS matrix2
            ON  matrix2.definition_id = def.id 
            AND matrix2.service_id IS NULL
            AND matrix2.provider_id = 24  ; 

Answer 2

嘗試以下方法（利用臨時表）：

CREATE TEMPORARY TABLE Results
select def.id, service_id, provider_id, 
 (case when matrix.amount is not null then matrix.amount else def.amount end) amount
    from billing_billingdefinition def 
        left outer join billing_billingmatrix matrix
        on matrix.definition_id=def.id 
    where (service_id = 25 or service_id is null)
      and (provider_id = 24 or provider_id is null);

SELECT * 
FROM Results r1
WHERE IFNULL(r1.service_id, 0) = 
      ( SELECT MAX(IFNULL(r2.service_id, 0)) 
        FROM Results r2 
        WHERE r2.id = r1.id
      );

SQL Fiddle僅用於第二部分（使用已經創建的Results表）

Answer 3

您需要使用max()來匯總金額max()當然還要添加group-by子句），以便在存在一個非null值的情況下獲得該值：

select
    def.id, service_id, provider_id, 
    max(case when matrix.amount is not null then matrix.amount else def.amount end) amount
    from billing_billingdefinition def 
    left outer join billing_billingmatrix matrix
        on matrix.definition_id=def.id 
    where (service_id = 25 or service_id is null)
    and (provider_id = 24 or provider_id is null)
   group by def.id, service_id, provider_id

Answer 4

這樣的事情也可能起作用。

select def.id, service_id, provider_id, IFNULL(matrix.amount,def.amount) amount
    from billing_billingdefinition def 
    left outer join (select definition_id, max(service_id) as maxsid from billing_billingmatrix matrix group by definition_id) as t1
        on def.id = t1.definition_id 
left outer join billing_billingmatrix matrix
    on matrix.definition_id=def.id and maxsid <=> service_id

Answer 5

嘗試這個：

SELECT BMD.id, BM.service_id, BM.provider_id, IFNULL(BM.amount, BMD.amount) AS amount 
FROM BillingMatrixDefinition BMD
LEFT JOIN BillingMatrix BM ON BMD.id = BM.definition_id AND (BM.service_id = 25 OR BM.provider_id = 24)
GROUP BY BMD.id;

Answer 6

我相信PM 771的答案在這里也適用，但是我決定在OUTER JOIN表中使用子選擇，以在加入之前對結果進行預過濾。

這是為此工作的最終SQL：

SELECT *,
       (CASE WHEN matrix.amount IS NOT NULL THEN matrix.amount ELSE def.amount END) calculated_amount,
    FROM billing_billingdefinition def
    LEFT OUTER JOIN
       (SELECT t.* FROM (
        select * from billing_billingmatrix 
        where (provider_id=25 
        or provider_id is null) 
        and (service_id=24 or service_id is null)
        ORDER BY service_id DESC
          ) t GROUP BY t.definition_id) matrix
            ON matrix.definition_id=def.id