[英]SQL Joining two tables but overwriting the first if it exists in the second
我無法使此查詢按我希望的方式工作。 我有兩個具有幾乎相同數據的表,但希望其中一個可以覆蓋另一個(如果存在)。 一個例子比嘗試解釋要容易:
有未調整的余額表:
所需的輸出將獲得未調整的余額,並在其之上應用任何現有的調整(如果is_current = 1)...本質上將替換該行,但仍保留原始的未調整的current_balance。
所需的輸出將是這樣的:
這是我當前的查詢無法正常工作...它正在翻轉值並缺少current_balance。 我已經嘗試了幾個小時,卻無法到達任何地方:
SELECT
*
FROM
(
SELECT
balance_adjustments.name,
balance_adjustments.user_id,
balance_adjustments.amount_owed,
balance_adjustments.when_to_pay,
balance_adjustments.current_balance
FROM
balance_adjustments
WHERE
balance_adjustments.when_to_pay = '2018-11-05'
AND balance_adjustments.is_current = true
UNION ALL
SELECT
unadjusted_balance.name,
unadjusted_balance.user_id,
unadjusted_balance.amount_owed,
unadjusted_balance.when_to_pay,
unadjusted_balance.current_balance
FROM
unadjusted_balance
LEFT OUTER JOIN balance_adjustments ON balance_adjustments.user_id = unadjusted_balance.user_id
AND balance_adjustments.name = unadjusted_balance.name
AND balance_adjustments.when_to_pay = unadjusted_balance.when_to_pay
AND balance_adjustments.is_current = true
WHERE
unadjusted_balance.when_to_pay = '2018-11-05'
AND balance_adjustments.name IS NULL
) AS table1
一些其他命令可幫助任何人設置此方案進行測試:
CREATE TABLE balance_adjustments
(
name varchar(30),
user_id varchar(30),
amount_owed float,
when_to_pay datetime,
current_balance float,
is_current boolean
);
CREATE TABLE unadjusted_balance
(
name varchar(30),
user_id varchar(30),
amount_owed float,
when_to_pay datetime,
current_balance float
);
insert into balance_adjustments values ('ricardo', '82340001', 100.00, '2018-11-05', null, 1)
insert into balance_adjustments values ('ricardo', '82340001', 33.00, '2018-11-05', null, 0)
insert into unadjusted_balance values ('joseph', '82340000', 2400.00, '2018-11-05', 4049.00)
insert into unadjusted_balance values ('ricardo', '82340001', 899.00, '2018-11-05', 500.00)
謝謝你的幫助
如果要使用余額調整覆蓋未調整的余額,請執行以下操作:
如果不為空,則Coalesce將返回第一個值,否則返回下一個參數的值。 如果左聯接未返回任何行,則總和的結果將為null。
詢問
SELECT ub.name
, ub.user_id
, COALESCE(SUM(ba.amount_owed), ub.amount_owed) AS amount_owed
, ub.when_to_pay
, ub.current_balance
FROM @unadjusted_balance AS ub
LEFT JOIN @balance_adjustments AS ba ON ba.user_id = ub.user_id AND ba.is_current = 1
GROUP BY ub.name, ub.user_id, ub.amount_owed, ub.when_to_pay, ub.current_balance;
我不確定您是否可以在is_current
等於1的情況下進行多個調整,如果最多只能有一行,則忽略聚合和分組,只需將ba.amount_owed作為第一個參數傳遞即可合並。
如果您只想用balance_adjustments
表中is_current
為1的值替換amount_owed
(我假設這些值只有一個),那么簡單的LEFT JOIN
和COALESCE
就足夠了。 COALESCE
確保balance_adjustments
表中不匹配的行中的任何NULL
值都被unadjusted_balances
表中的原始值替換。 從您的問題尚不清楚,您是否也想替換when_to_pay
字段,我假設您在此查詢中也有。 如果不這樣做,只需更換COALESCE(ba.when_to_pay, ub.when_to_pay) AS when_to_pay
與ub.when_to_pay
。
SELECT ub.name, ub.user_id,
COALESCE(ba.amount_owed, ub.amount_owed) AS amount_owed,
COALESCE(ba.when_to_pay, ub.when_to_pay) AS when_to_pay,
ub.current_balance
FROM unadjusted_balance ub
LEFT JOIN balance_adjustments ba ON ba.user_id = ub.user_id AND ba.is_current
ORDER BY ub.name
輸出:
name user_id amount_owed when_to_pay current_balance
joseph 82340000 2400 2018-11-05 00:00:00 4049
ricardo 82340001 100 2018-11-05 00:00:00 500
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