Question

我有以下查询

INSERT INTO address (house_number, street, city_id)
    values(11, 'test st', (select id from city where LOWER(city) = LOWER('somecity')))

如果city中不存在“ somecity”，那么是否仍要在city表中插入“ somecity”，然后在插入之后，它将返回插入行的ID？

我确实找到了答案，说可以使用upsert实现此目的

https://stackoverflow.com/a/31742830/492015

但是我找不到一个示例，如果select未返回该行，则会插入该示例。

Answer 1

您可以use a CTE to perform the INSERTs one after the other but as a single statement来代替嵌套INSERT：

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 *

使用此设置：

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');

以及上面的INSERT命令，查询

SELECT * FROM test_address;

收益

| house_number | street  | city_id |
|--------------+---------+---------|
|           11 | test st |       1 |

和

SELECT * FROM test_city;

收益

| id | city     |
|----+----------|
|  1 | somecity |

请注意，CTE取代了

(select id from city where LOWER(city) = LOWER('somecity'))

带有INSERT .. ON CONFLICT .. DO UPDATE语句：

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代替了DO NOTHING，以便RETURNING id, city总是返回某些内容。如果您使用DO NOTHING，则在发生冲突时不会返回任何内容。

但是请注意，使用city = excluded.city的结果是原始的'Somecity' 被'somecity'取代。我不确定您是否会认为这种行为可以接受，但是很遗憾，我还没有弄清楚在发生冲突时如何不执行任何操作，但同时又返回了id和city。 / p>

上述解决方案的另一个问题是，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));

这允许您在INSERT语句中使用相同的条件：

INSERT ... ON CONFLICT (lower(city))

代替出现在SELECT语句中的条件LOWER(city) = LOWER('somecity')。它产生了预期的效果，但是要权衡的是，现在您有了唯一的索引在(lower(city))上。

关于followup question 如何插入两个以上的表：

您可以chain together more than one CTE，随后的CTE甚至可以引用以前的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

PostgreSQL插入如果不存在

1 个答案: