SQLAlchemy 中的 VALUES 子句 [英] VALUES clause in SQLAlchemy

问题描述

有没有办法在 SQLAlchemy 中构建一个 Query 对象，它相当于:

Is there a way to build a Query object in SQLAlchemy which will be the equivalent of:

SELECT * FROM (VALUES (1, 2, 3)) AS sq;

从我在文档中看到的内容来看，VALUES 子句仅与 INSERT 一起使用.

From what I see in the documentation, the VALUES clause appears only in use with INSERT.

推荐答案

插入中的VALUES"是标准 SQL，独立的VALUES"关键字是 Postgresql 的东西.在 PGValues 上有一个快速编译器配方(复制到这里以防我更改维基有一天):

well "VALUES" in an insert is the standard SQL, the standalone "VALUES" keyword is a Postgresql thing. There's a quick compiler recipe for this one at PGValues (copied here in case I change the wiki someday):

from sqlalchemy import *
from sqlalchemy.ext.compiler import compiles
from sqlalchemy.sql.expression import FromClause
from sqlalchemy.sql import table, column

class values(FromClause):
    def __init__(self, *args):
        self.list = args

    def _populate_column_collection(self):
        self._columns.update(
            [("column%d" % i, column("column%d" % i))
                    for i in xrange(1, len(self.list[0]) + 1)]
        )

@compiles(values)
def compile_values(element, compiler, asfrom=False, **kw):
    v = "VALUES %s" % ", ".join(
        "(%s)" % ", ".join(compiler.render_literal_value(elem, None) for elem in tup)
        for tup in element.list
    )
    if asfrom:
        v = "(%s)" % v
    return v

if __name__ == '__main__':
    t1 = table('t1', column('a'), column('b'))
    t2 = values((1, 0.5), (2, -0.5)).alias('weights')
    print select([t1, t2]).select_from(t1.join(t2, t1.c.a==t2.c.column2))

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