通过MySQLdb创建函数

Question

如何在 python 中使用 MySQLdb 库定义多语句函数或过程？

示例：

import MySQLdb

db = MySQLdb.connect(db='service')

c = db.cursor()

c.execute("""DELIMITER //
CREATE FUNCTION trivial_func (radius float) 
    RETURNS FLOAT

    BEGIN
    IF radius > 1 THEN
        RETURN 0.0;
    ELSE
        RETURN 1.0;
    END IF;
END //

DELIMITER ;""")

这会创建以下回溯：

Traceback (most recent call last):
  File "proof.py", line 21, in <module>
    DELIMITER ;""")
  File "build/bdist.macosx-10.5-i386/egg/MySQLdb/cursors.py", line 173, in execute
  File "build/bdist.macosx-10.5-i386/egg/MySQLdb/connections.py", line 35, in defaulterrorhandler
_mysql_exceptions.ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DELIMITER //\nCREATE FUNCTION trivial_func (radius float) \n    RETURNS FLOAT\n\n   ' at line 1")

如果我将相同的 SQL 直接复制到 mysql shell 客户端，它会按预期工作

Answer 1

DELIMITER

命令是内置的MySQL shell客户端，它只能被该程序（和MySQL查询浏览器）识别。如果直接通过 API 执行 SQL 语句，则无需使用

DELIMITER

。

DELIMITER

的目的是帮助您避免在

CREATE FUNCTION

语句终止时出现歧义（当语句本身可以包含分号字符时）。这在 shell 客户端中很重要，默认情况下分号终止 SQL 语句。您需要将语句终止符设置为其他字符才能提交函数（或触发器或过程）的主体。

CREATE FUNCTION trivial_func (radius float) 
    RETURNS FLOAT

    BEGIN
    IF radius > 1 THEN
        RETURN 0.0; <-- does this semicolon terminate RETURN or CREATE FUNCTION?
    ELSE
        RETURN 1.0;
    END IF;
END

由于 API 通常允许您一次提交一个 SQL 语句，因此不会有任何歧义——接口知道函数定义体内的任何分号都不会终止整个

CREATE FUNCTION

语句。所以不需要用

DELIMITER

来改变语句终止符。

Answer 2

要添加 Bill Karwin 的答案，可以使用以下 python 代码示例来正确执行使用 DELIMITER 的字符串，例如数据库创建脚本。

import MySQLdb

db = MySQLdb.connect(db='service')
cursor = db.cursor()

dbString = """DELIMITER //
CREATE FUNCTION trivial_func (radius float) 
RETURNS FLOAT

BEGIN
IF radius > 1 THEN
    RETURN 0.0;
ELSE
    RETURN 1.0;
END IF;
END //

DELIMITER ;"""

# Find special delimiters
delimiters = re.compile('DELIMITER *(\S*)',re.I)
result = delimiters.split(dbString)

# Insert default delimiter and separate delimiters and sql
result.insert(0,';') 
delimiter = result[0::2]
section   = result[1::2]

# Split queries on delimiters and execute
for i in range(len(delimiter)):
    queries = section[i].split(delimiter[i])
    for query in queries:
        if not query.strip():
            continue
        cursor.execute(query)

这将一次执行一个分隔语句，并在需要时更改分隔符。

Answer 3

基于@AaronS 的评论。该脚本将读取 SQL 文件，将其拆分为离散的 SQL 命令并处理它找到的任何分隔符。

    queries = []
    delimiter = ';'
    query = ''
    with open('import.sql', 'r') as f:
        for line in f.readlines():
            line = line.strip()
            if line.startswith('DELIMITER'):
                delimiter = line[10:]
            else:
                query += line+'\n'
                if line.endswith(delimiter):
                    # Get rid of the delimiter, remove any blank lines and add this query to our list
                    queries.append(query.strip().strip(delimiter))
                    query = ''

    for query in queries:
        if not query.strip():
            continue
        cursor.execute(query)
    cursor.close()

Answer 4

基于@DenisH 的评论。它可以解决一个 SQL 命令字符串中指定的多个语句。

def execute_muti(cursor, sql_commands):
queries = []
delimiter = ';'
query = ''
for line in sql_commands.split('\n'):
    line = line.strip()
    if line.lower().startswith('delimiter'):  # Find special delimiters
        delimiter = line[10:].strip()
    else:
        query += line + '\n'
        if line.endswith(delimiter):
            query = query.strip()[:-len(delimiter)]
            queries.append(query)
            query = ''
for query in queries:
    if not query.strip():
        continue
    results = cursor.execute(query, multi=True)
    for result in results:
        if result.with_rows:
            print("Rows produced by statement '{}':".format(result.statement))
            print(result.fetchall())
        else:
            print("Number of rows affected by statement '{}': {}".format(
                result.statement,
                result.rowcount
            ))

以下示例展示了如何使用它：

import mysql.connector

with mysql.connector.connect(host='localhost', port=3306, user='root', password='test') as db:
    with db.cursor() as cursor:
        sql = 'INSERT YOUR SQL CODE HERE!!'
        execute_muti(cursor, sql)