Postgres:如果不存在则插入

我使用Python写postgres数据库:

sql_string = "INSERT INTO hundred (name,name_slug,status) VALUES ("
sql_string += hundred + ", '" + hundred_slug + "', " + status + ");"
cursor.execute(sql_string)

但由于我的一些行是相同的，我得到以下错误:

psycopg2.IntegrityError: duplicate key value  
  violates unique constraint "hundred_pkey"

我怎么能写一个'插入，除非这行已经存在' SQL语句?

我见过这样的复杂语句:

IF EXISTS (SELECT * FROM invoices WHERE invoiceid = '12345')
UPDATE invoices SET billed = 'TRUE' WHERE invoiceid = '12345'
ELSE
INSERT INTO invoices (invoiceid, billed) VALUES ('12345', 'TRUE')
END IF

但首先，这对我需要的东西来说是不是太过了，其次，我怎么能把它们作为一个简单的字符串来执行呢?

当前回答

你可以在Postgres中使用VALUES:

INSERT INTO person (name)
    SELECT name FROM person
    UNION 
    VALUES ('Bob')
    EXCEPT
    SELECT name FROM person;

2012-03-30 09:02:24

其他回答

在PostgreSQL中使用WITH查询有一个很好的方法来执行有条件的INSERT: 如:

WITH a as(
select 
 id 
from 
 schema.table_name 
where 
 column_name = your_identical_column_value
)
INSERT into 
 schema.table_name
(col_name1, col_name2)
SELECT
    (col_name1, col_name2)
WHERE NOT EXISTS (
     SELECT
         id
     FROM
         a
        )
  RETURNING id

2017-10-14 04:26:56

您的列“hundred”似乎被定义为主键，因此必须是唯一的，但事实并非如此。问题不在于你，而在于你的数据。

我建议您插入一个id作为串行类型来处理主键

2018-08-30 12:34:05

有规则很简单:

CREATE RULE file_insert_defer AS ON INSERT TO file
WHERE (EXISTS ( SELECT * FROM file WHERE file.id = new.id)) DO INSTEAD NOTHING

但是并发写失败了…

2016-07-12 08:52:16

不幸的是，PostgreSQL既不支持MERGE也不支持ON DUPLICATE KEY UPDATE，所以你必须在两个语句中完成:

UPDATE  invoices
SET     billed = 'TRUE'
WHERE   invoices = '12345'

INSERT
INTO    invoices (invoiceid, billed)
SELECT  '12345', 'TRUE'
WHERE   '12345' NOT IN
        (
        SELECT  invoiceid
        FROM    invoices
        )

你可以把它包装成一个函数:

CREATE OR REPLACE FUNCTION fn_upd_invoices(id VARCHAR(32), billed VARCHAR(32))
RETURNS VOID
AS
$$
        UPDATE  invoices
        SET     billed = $2
        WHERE   invoices = $1;

        INSERT
        INTO    invoices (invoiceid, billed)
        SELECT  $1, $2
        WHERE   $1 NOT IN
                (
                SELECT  invoiceid
                FROM    invoices
                );
$$
LANGUAGE 'sql';

就叫它:

SELECT  fn_upd_invoices('12345', 'TRUE')

2010-11-01 14:28:27

你可以在Postgres中使用VALUES:

INSERT INTO person (name)
    SELECT name FROM person
    UNION 
    VALUES ('Bob')
    EXCEPT
    SELECT name FROM person;

2012-03-30 09:02:24

Postgres:如果不存在则插入

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