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?
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')
一种方法是创建一个不受约束(没有唯一索引)的表，将所有数据插入其中，并执行与插入到百位表不同的选择。
所以高水平。我假设在我的示例中所有三个列都是不同的，因此对于step3，将NOT EXITS连接更改为只连接100表中唯一的列。
Create temporary table. See docs here.
CREATE TEMPORARY TABLE temp_data(name, name_slug, status);
INSERT Data into temp table.
INSERT INTO temp_data(name, name_slug, status);
Add any indexes to the temp table.
Do main table insert.
INSERT INTO hundred(name, name_slug, status)
SELECT DISTINCT name, name_slug, status
FROM hundred
WHERE NOT EXISTS (
SELECT 'X'
FROM temp_data
WHERE
temp_data.name = hundred.name
AND temp_data.name_slug = hundred.name_slug
AND temp_data.status = status
);
我知道这个问题是很久以前提出的，但我想这可能会对一些人有所帮助。我认为最简单的方法就是触发。例如:
Create Function ignore_dups() Returns Trigger
As $$
Begin
If Exists (
Select
*
From
hundred h
Where
-- Assuming all three fields are primary key
h.name = NEW.name
And h.hundred_slug = NEW.hundred_slug
And h.status = NEW.status
) Then
Return NULL;
End If;
Return NEW;
End;
$$ Language plpgsql;
Create Trigger ignore_dups
Before Insert On hundred
For Each Row
Execute Procedure ignore_dups();
从psql提示符(或者您喜欢的直接在数据库上执行查询的方式)执行这段代码。然后你可以像往常一样从Python中插入。例如:
sql = "Insert Into hundreds (name, name_slug, status) Values (%s, %s, %s)"
cursor.execute(sql, (hundred, hundred_slug, status))
注意，正如@Thomas_Wouters已经提到的，上面的代码利用了参数，而不是连接字符串。
我怎么能写一个'插入，除非这行已经存在' SQL语句?
在PostgreSQL中有一个很好的方法来执行有条件的INSERT:
INSERT INTO example_table
(id, name)
SELECT 1, 'John'
WHERE
NOT EXISTS (
SELECT id FROM example_table WHERE id = 1
);
注意:对于并发写操作，这种方法不是100%可靠的。在NOT EXISTS反半连接中的SELECT和INSERT本身之间有一个非常小的竞争条件。在这种情况下，它可能会失败。
我正在寻找一个类似的解决方案，试图找到在PostgreSQL和HSQLDB中工作的SQL。(HSQLDB使这变得困难。)以你的例子为基础，这是我在其他地方发现的格式。
sql = "INSERT INTO hundred (name,name_slug,status)"
sql += " ( SELECT " + hundred + ", '" + hundred_slug + "', " + status
sql += " FROM hundred"
sql += " WHERE name = " + hundred + " AND name_slug = '" + hundred_slug + "' AND status = " + status
sql += " HAVING COUNT(*) = 0 );"
这是一个通用的python函数，给定表名，列和值，生成相当于postgresql的upsert。
进口json
def upsert(table_name, id_column, other_columns, values_hash):
template = """
WITH new_values ($$ALL_COLUMNS$$) as (
values
($$VALUES_LIST$$)
),
upsert as
(
update $$TABLE_NAME$$ m
set
$$SET_MAPPINGS$$
FROM new_values nv
WHERE m.$$ID_COLUMN$$ = nv.$$ID_COLUMN$$
RETURNING m.*
)
INSERT INTO $$TABLE_NAME$$ ($$ALL_COLUMNS$$)
SELECT $$ALL_COLUMNS$$
FROM new_values
WHERE NOT EXISTS (SELECT 1
FROM upsert up
WHERE up.$$ID_COLUMN$$ = new_values.$$ID_COLUMN$$)
"""
all_columns = [id_column] + other_columns
all_columns_csv = ",".join(all_columns)
all_values_csv = ','.join([query_value(values_hash[column_name]) for column_name in all_columns])
set_mappings = ",".join([ c+ " = nv." +c for c in other_columns])
q = template
q = q.replace("$$TABLE_NAME$$", table_name)
q = q.replace("$$ID_COLUMN$$", id_column)
q = q.replace("$$ALL_COLUMNS$$", all_columns_csv)
q = q.replace("$$VALUES_LIST$$", all_values_csv)
q = q.replace("$$SET_MAPPINGS$$", set_mappings)
return q
def query_value(value):
if value is None:
return "NULL"
if type(value) in [str, unicode]:
return "'%s'" % value.replace("'", "''")
if type(value) == dict:
return "'%s'" % json.dumps(value).replace("'", "''")
if type(value) == bool:
return "%s" % value
if type(value) == int:
return "%s" % value
return value
if __name__ == "__main__":
my_table_name = 'mytable'
my_id_column = 'id'
my_other_columns = ['field1', 'field2']
my_values_hash = {
'id': 123,
'field1': "john",
'field2': "doe"
}
print upsert(my_table_name, my_id_column, my_other_columns, my_values_hash)
