在 pg8000 中使用 % 通配符

Question

我有一个类似于下面的查询：

def connection():
    pcon = pg8000.connect(host='host', port=1234, user='user', password='password', database = 'database')
    return pcon, pcon.cursor()

pcon, pcur = connection()
query = """ SELECT * FROM db WHERE (db.foo LIKE 'string-%' OR db.foo LIKE 'bar-%')"""
db = pd.read_sql_query(query, pcon)

然而，当我尝试运行我得到的代码时：

DatabaseError: '%'' not supported in a quoted string within the query string

我试过使用 \ 和额外的 % 转义符号，但没有成功。我怎样才能让 pg8000 正确地将其视为通配符？

Answer 1

"In Python, % usually refers to a variable that follows the string. If you want a literal percent sign, then you need to double it. %%"

-- Source

LIKE 'string-%%'

否则，如果这不起作用，PostgreSQL 也支持 underscores for pattern matching。

'abc' LIKE 'abc'    true
'abc' LIKE 'a%'     true
'abc' LIKE '_b_'    true

但是，正如评论中提到的，

An underscore (_) in pattern stands for (matches) any single character; a percent sign (%) matches any sequence of zero or more characters

不过，根据 source code，问题似乎是 LIKE 语句中 % 后面的单引号。

if next_c == "%":
    in_param_escape = True
else:
    raise InterfaceError(
        "'%" + next_c + "' not supported in a quoted "
        "string within the query string")

所以如果 next_c == "'" 而不是 next_c == "%"，那么你会得到你的错误

'%'' not supported in a quoted string within the query string

Answer 2

使用最新版本的 pg8000，LIKE 中的 % 应该不会有任何问题。例如：

>>> import pg8000.dbapi
>>>
>>> con = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cur = con.cursor()
>>> cur.execute("CREATE TEMPORARY TABLE book (id SERIAL, title TEXT)")
>>> for title in ("Ender's Game", "The Magus"):
...     cur.execute("INSERT INTO book (title) VALUES (%s)", [title])
>>>
>>> cur.execute("SELECT * from book WHERE title LIKE 'The %'")
>>> cur.fetchall()
([2, 'The Magus'],)

在 pg8000 中使用 % 通配符

Using % wildcard with pg8000

python

pg8000