Question

我正在尝试使用查询API创建具有MAX_EXECUTION_TIME（30000）提示的MySQL查询。

我的代码大致是：

from flask_sqlalchemy import SQLAlchemy

class MyTable(SQLAlchemy().Model):
  ...

base_query = Sqlalchemy.session.query(MyTable) # This works when I execute it.
base_query_with_hint = base_query.with_hint(MyTable, "MAX_EXECUTION_TIME(30000)")
base_query_with_hint.execute() # THIS DOES NOT WORK.

str(base_query_with_hint) 
# Output
# Select a, b, c from MyTable MAX_EXECUTION_TIME(30000)

很明显，提示只是在查询结束时呈现！

应呈现为

Select /*+ MAX_EXECUTION_TIME(30000) */ a, b, c from MyTable

我希望它的行为与https://docs.sqlalchemy.org/en/13/core/selectable.html#sqlalchemy.sql.expression.Select.with_hint完全一样，但是我使用的是Query API而不是Select API。

Answer 1

简而言之，请改用prefix_with()。

下面是来自SQLAlchemy documentation的MySQL 5.7优化器提示的类似示例，该示例在Python交互式提示中运行：

>>> from sqlalchemy.sql import select, table
>>> from sqlalchemy.dialects import mysql
>>> tbl = table('my_table')
>>> # MySQL 5.7 optimizer hints
>>> stmt = select([tbl]).prefix_with(
...     "/*+ MAX_EXECUTION_TIME(1000) */", dialect="mysql")
>>> print(stmt.compile(dialect=mysql.dialect()))
SELECT /*+ MAX_EXECUTION_TIME(1000) */  
FROM my_table
>>>

SQLAlchemy查询API不能正确使用提示

1 个答案: