[英]Postgresql insert if does not exist
我有以下查詢
INSERT INTO address (house_number, street, city_id)
values(11, 'test st', (select id from city where LOWER(city) = LOWER('somecity')))
無論如何,如果在city
中不存在“ somecity”,那么是否在city
表中插入“ somecity”,然后在插入之后,它將返回插入行的ID?
我確實找到了這個答案,說可以使用upsert實現此目的
https://stackoverflow.com/a/31742830/492015
但是我找不到一個如果select不返回該行插入的示例。
除了嵌套INSERT,您還可以使用CTE一個接一個地執行INSERT,一個語句即可 :
WITH tmp AS (
INSERT INTO test_city (city) VALUES ('somecity')
ON CONFLICT (lower(city)) DO UPDATE SET city = excluded.city
RETURNING id, city
)
INSERT INTO test_address (house_number, street, city_id)
SELECT house_number, street, id
FROM (VALUES (11, 'test st', 'somecity')) val (house_number, street, city)
LEFT JOIN tmp USING (city)
RETURNING *
使用此設置:
DROP TABLE IF EXISTS test_address;
DROP TABLE IF EXISTS test_city;
CREATE TABLE test_address (
house_number int
, street text
, city_id int
);
CREATE TABLE test_city (
id int GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY
, city text
);
CREATE UNIQUE INDEX test_city_uniq_idx ON test_city USING btree (lower(city));
INSERT INTO test_city (city) VALUES ('Somecity');
和上面的INSERT一起,查詢
SELECT * FROM test_address;
產量
| house_number | street | city_id |
|--------------+---------+---------|
| 11 | test st | 1 |
和
SELECT * FROM test_city;
產量
| id | city |
|----+----------|
| 1 | somecity |
請注意,CTE取代了
(select id from city where LOWER(city) = LOWER('somecity'))
用INSERT .. ON CONFLICT .. DO UPDATE語句:
INSERT INTO test_city (city) VALUES ('somecity')
ON CONFLICT (lower(city)) DO UPDATE SET city = excluded.city
RETURNING id, city
我使用DO UPDATE
而不是DO NOTHING
以便RETURNING id, city
將始終返回某些內容。 如果使用DO NOTHING
,則在發生沖突時不返回任何內容。
但是請注意,使用的結果, city = excluded.city
是,原來的'Somecity'
被替換為'somecity'
。 我不確定您是否會接受這種行為,但是不幸的是,在發生沖突時,我還沒有弄清楚如何執行任何操作,但同時返回了id
和city
。
您可能會遇到上述解決方案的另一個問題是,我在lower(city)
上使用了唯一索引:
CREATE UNIQUE INDEX test_city_uniq_idx ON test_city USING btree (lower(city));
這使您可以在INSERT語句中使用相同的條件:
INSERT ... ON CONFLICT (lower(city))
替換出現在SELECT語句中的條件LOWER(city) = LOWER('somecity')
。 它產生了預期的效果,但是要權衡的是,現在您在(lower(city))
上具有唯一索引。
關於如何插入兩個以上表的后續問題 :
您可以將多個CTE鏈接在一起 ,后續的CTE甚至可以引用先前的CTE。 例如,
CREATE UNIQUE INDEX city_uniq_idx ON city USING btree (lower(city));
CREATE UNIQUE INDEX state_uniq_idx ON state USING btree (lower(state_code));
WITH tmpcity AS
(
INSERT INTO
city (city)
VALUES
(
'Miami'
)
ON CONFLICT (lower(city)) DO
UPDATE
SET
city = excluded.city RETURNING id, city
)
, tmpstate as
(
INSERT INTO
state (state_code)
VALUES
(
'FL'
)
ON CONFLICT (lower(state_code)) DO
UPDATE
SET
state_code = excluded.state_code RETURNING id, state_code
)
INSERT INTO
address (house_number, street, city_id, state_id)
SELECT
house_number,
street,
tmpcity.id,
tmpstate.id
FROM
(
VALUES
(
12,
'fake st.',
'Miami',
'FL'
)
)
val (house_number, street, city, state_code)
LEFT JOIN
tmpcity USING (city)
LEFT JOIN
tmpstate USING (state_code)
ON CONFLICT (street) DO NOTHING
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