Question

如果数据库中存在artist，我如何将这些does not插入数据库。我写了以下代码。但这是错误的。你能帮帮我吗？感谢

艺术家名单

Lata Mangeshkar  
Lata Mangeshkar
Lata Mangeshkar
Asha Bhosle
Lata Mangeshkar
Mahendra Kapoor  
Lata Mangeshkar
Kishore Kumar
Lata Mangeshkar

我的代码

for l in artist:
        l = l.strip()
        cursor.execute("SELECT id FROM song_artist WHERE name = %s ;" ,(l,) ) # Id exist?
        artist_rows = cursor.fetchone()
        if not artist_rows:
            artist_slug = self.makeSlug(artist[0])
            cursor.execute( 'INSERT INTO song_artist (name,slug) VALUES (%s,%s) RETURNING id;',(artist[0],artist_slug))
            print k

输出：

INSERT INTO song_artist (name,slug) VALUES (Lata Mangeshkar,lata-mangeshkar) RET
URNING id;
INSERT INTO song_artist (name,slug) VALUES (Lata Mangeshkar,lata-mangeshkar) RET
URNING id;
INSERT INTO song_artist (name,slug) VALUES (Lata Mangeshkar,lata-mangeshkar) RET
URNING id;
INSERT INTO song_artist (name,slug) VALUES (Lata Mangeshkar,lata-mangeshkar) RET
URNING id;
INSERT INTO song_artist (name,slug) VALUES (Asha Bhosle,asha-bhosle) RETURNING i
d;
INSERT INTO song_artist (name,slug) VALUES (Lata Mangeshkar,lata-mangeshkar) RET
URNING id;
INSERT INTO song_artist (name,slug) VALUES (Mahendra Kapoor,mahendra-kapoor) RET
URNING id;
INSERT INTO song_artist (name,slug) VALUES (Mahendra Kapoor,mahendra-kapoor) RET
URNING id;
INSERT INTO song_artist (name,slug) VALUES (Lata Mangeshkar,lata-mangeshkar) RET
URNING id;

输出应该是：

INSERT INTO song_artist (name,slug) VALUES (Asha Bhosle,asha-bhosle) RETURNING i
d;
INSERT INTO song_artist (name,slug) VALUES (Lata Mangeshkar,lata-mangeshkar) RET
URNING id;
INSERT INTO song_artist (name,slug) VALUES (Mahendra Kapoor,mahendra-kapoor) RET
URNING id;

更新：

我已经在列名上添加了约束来强制列是唯一的。

Answer 1

在数据库端强制执行该操作。在列名称上添加约束以强制列是唯一的。这应该足够了：

ALTER TABLE song_artist ADD UNIQUE（name）;

通过这种方式，您可以确定无论您做什么，都不会有任何重复的值。
您可以使用以下查询插入数据：

INSERT INTO song_artist（name，slug）
选择'Mahendra Kapoor'，'mahendra-kapoor' 什么不存在
  （
    选择42
    来自song_artist
    名字='Mahendra Kapoor'   ）;

Answer 2

您可以添加Szymon Guz建议的唯一约束，

ALTER TABLE song_artist ADD UNIQUE (name);

然后使用try / except来处理重复错误：

try:
  cursor.execute( 'INSERT INTO song_artist (name,slug) VALUES (%s,%s) RETURNING id;',(artist[0],artist_slug))

except psycopg2.IntegrityError:
  debug.print 'Duplicate values found.  Insert was not successful'

Answer 3

你必须使用if not artist_rows:这就是全部

    artist_slug = self.makeSlug(l)

cursor.execute("SELECT count(id) FROM song_artist WHERE name = %s and slug = %s ;" ,(l,artist_slug) ) # Id exist?
artist_rows = cursor.fetchone()
#artist_rows = artist_rows[0]
db.commit()
if not artist_rows:
cursor.execute( 'INSERT INTO song_artist (name,slug) VALUES (%s,%s) RETURNING id;',(l,artist_slug))
#k=( 'INSERT INTO song_artist (name,slug) SELECT %s,%s WHERE NOT EXISTS ( SELECT 42 FROM song_artist WHERE name = %s) RETURNING id;'%(l,artist_slug,l))
artist_id = cursor.fetchone()[0] # get mysql_insert_id using RETURNING
db.commit()

避免重复数据PostgreSQL

3 个答案: