test_tablesample.py

from sqlalchemy import Column
from sqlalchemy import column
from sqlalchemy import Integer
from sqlalchemy import String
from sqlalchemy import Table
from sqlalchemy import table
from sqlalchemy import tablesample
from sqlalchemy.engine import default
from sqlalchemy.sql import func
from sqlalchemy.sql import select
from sqlalchemy.sql import text
from sqlalchemy.sql.selectable import TableSample
from sqlalchemy.testing import assert_raises_message
from sqlalchemy.testing import AssertsCompiledSQL
from sqlalchemy.testing import fixtures


class TableSampleTest(fixtures.TablesTest, AssertsCompiledSQL):
    __dialect__ = default.DefaultDialect(supports_native_boolean=True)

    run_setup_bind = None

    run_create_tables = None

    @classmethod
    def define_tables(cls, metadata):
        Table(
            "people",
            metadata,
            Column("people_id", Integer, primary_key=True),
            Column("age", Integer),
            Column("name", String(30)),
        )

    def test_standalone(self):
        table1 = self.tables.people

        # no special alias handling even though clause is not in the
        # context of a FROM clause
        self.assert_compile(
            tablesample(table1, 1, name="alias"),
            "people AS alias TABLESAMPLE system(:system_1)",
        )

        self.assert_compile(
            table1.tablesample(1, name="alias"),
            "people AS alias TABLESAMPLE system(:system_1)",
        )

        self.assert_compile(
            tablesample(
                table1, func.bernoulli(1), name="alias", seed=func.random()
            ),
            "people AS alias TABLESAMPLE bernoulli(:bernoulli_1) "
            "REPEATABLE (random())",
        )

    def test_select_from(self):
        table1 = self.tables.people

        self.assert_compile(
            select(table1.tablesample(text("1"), name="alias").c.people_id),
            "SELECT alias.people_id FROM "
            "people AS alias TABLESAMPLE system(1)",
        )

    def test_no_alias_construct(self):
        a = table("a", column("x"))

        assert_raises_message(
            NotImplementedError,
            "The TableSample class is not intended to be constructed "
            "directly.  "
            r"Please use the tablesample\(\) standalone",
            TableSample,
            a,
            "foo",
        )