SQLAlchemy 如何在大查询中添加注释？

Question

我正在使用SQLAlchemy 创建 SQL 语句，这些语句稍后会使用sqlparse 格式化。

有些查询的复杂性可以从评论中受益。有没有办法让 SQLAlchemy 输出如下查询：

选择富， -- 评论解释复杂的案例陈述 CASE WHEN .. END 为 complex_case 从栏 其中 1=1 -- 解释 EXISTS 子句用途的注释 并且存在（选择...）

Answer 1

Mike Bayer 向 wiki 添加了一个 POC，该 POC 将 .comment() 方法添加到所有子句元素，以便可以将 SQL cmets 添加到单个元素。 https://bitbucket.org/zzzeek/sqlalchemy/wiki/UsageRecipes/CompiledComments

```

from sqlalchemy import Table, Column, MetaData, Integer
from sqlalchemy import select, case, func, exists

m = MetaData()

foo = Table(
    'foo', m,
    Column('a', Integer),
    Column('b', Integer)
)

bar = Table(
    'bar', m,
    Column('x', Integer),
    Column('y', Integer),
    Column('z', Integer)
)

subq = select([foo.c.a]).where(foo.c.b > 10).alias()
stmt = select([
    bar.c.x,
    case([
        (bar.c.y == 5, "A"),
        (bar.c.y == 10, "B")
    ], else_="C").label("complicated_case").
    comment("comment explaining the convoluted case statement"),
    func.row_number().over(order_by=bar.c.z).label("complicated_row_num").
    comment("comment exaplaining the convoluted window function")
]).select_from(
    bar.join(
        subq.comment("Comment explaining subquery and join"),
        bar.c.x == subq.c.a
    )
).where(
    exists([foo.c.b]).where(foo.c.a == bar.c.y).
    comment("comment explaining the purpose of the EXISTS clause")
)

print stmt

"""

output:

SELECT bar.x,
-- comment explaining the convoluted case statement
CASE WHEN (bar.y = :y_1) THEN :param_1 WHEN (bar.y = :y_2) THEN :param_2 ELSE :param_3 END AS complicated_case,
-- comment exaplaining the convoluted window function
row_number() OVER (ORDER BY bar.z) AS complicated_row_num
FROM bar JOIN
-- Comment explaining subquery and join
(SELECT foo.a AS a
FROM foo
WHERE foo.b > :b_1) AS anon_1 ON bar.x = anon_1.a
WHERE
-- comment explaining the purpose of the EXISTS clause
EXISTS (SELECT foo.b
FROM foo
WHERE foo.a = bar.y)

"""

```