[英]How to select from table depend on value from another table column
如何使sql
語句select
哪個table
取決於另一個table
值,如下所示:
SELECT b.*, detail.*, t.date
FROM board AS b, transaction AS t,
(CASE t.type
WHEN 0 THEN (SELECT * FROM claim)
WHEN 1 THEN (SELECT * FROM retrieve)
END) AS detail
WHERE b.sn='D92AD006325' AND b.id=t.board_id AND detail.id=t.transaction_id
表的某些部分如下所示:
| board | | transaction | | claim | | retrieve |
|-------| |-----------------| |-----------| |----------|
| ... | | board_id | | id | | id |
|_______| | transaction_id | | sender | | code |
| type | | location | |__________|
| date | |___________|
|_________________|
如果type = 0
, transaction_id
裝置claim.id
,否則retrieve.id
所以輸出可能像這樣:
| board.id | ... | claim.id | claim.sender | location | retrieve.id | retrieve.code | date |
|----------|-----|----------|--------------|-----------|-------------|---------------|------------------|
| 19 | ... | 10 | SenderA | locationA | | | 10/09/2015 18:09 |
| 19 | ... | | | | 8 | 58/03165 | 14/09/2015 11:10 |
| 19 | ... | 14 | SenderB | locationA | | | 20/09/2015 08:10 |
兩個簡單的聯接和簡單的過濾器比一個復雜的聯接要好得多。
SELECT b.*, c.number, c.location, t.type, t.date
FROM board AS b, transaction AS t, claim AS c
WHERE b.sn='D92AD006325' AND b.id=t.board_id AND c.id=t.transaction_id AND t.type=0
UNION ALL
SELECT b.*, r.number, NULL AS location, t.type, t.date
FROM board AS b, transaction AS t, retrieve AS r
WHERE b.sn='D92AD006325' AND b.id=t.board_id AND r.id=t.transaction_id AND t.type=1
或者,使用外部聯接將兩個表聯接在一起,並在列中使用過濾器:
SELECT b.*,
case when t.type = 0 then c.number else r.number end as number,
case when t.type = 0 then c.location else null end as location,
t.type,
t.date
FROM board AS b
INNER JOIN transaction AS t,
ON (b.id=t.board_id)
LEFT OUTER JOIN claim c
ON (c.id=t.transaction_id and t.type = 0)
LEFT OUTER JOIN retrieve r
ON (r.id=t.transaction_id and t.type = 1)
WHERE b.sn='D92AD006325'
我建議使用動態SQL查詢。 這將使SQL運行邏輯更簡單,易讀且易於維護。
我嘗試指定和命名兩個表中的每一列進行匹配,並使用NULL
替換retrieve
表中的缺失列,如下所示:
SELECT b.*, c.number, c.location, t.type, t.date
FROM board AS b, transaction AS t, claim AS c
WHERE b.sn='D92AD006325' AND b.id=t.board_id AND c.id=t.transaction_id AND t.type=0
UNION ALL
SELECT b.*, r.number, NULL AS location, t.type, t.date
FROM board AS b, transaction AS t, retrieve AS r
WHERE b.sn='D92AD006325' AND b.id=t.board_id AND r.id=t.transaction_id AND t.type=1
現在對我來說是工作。
還有更好的方法嗎?
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