TTL param for engine

[aamalev]

Implementation for TTL

CREATE TABLE example_table
(
    d DateTime,
    a Int
)
ENGINE = MergeTree
PARTITION BY toYYYYMM(d)
ORDER BY d
TTL d + INTERVAL 1 MONTH [DELETE],
    d + INTERVAL 1 WEEK TO VOLUME 'aaa',
    d + INTERVAL 2 WEEK TO DISK 'bbb';

Usage

    from clickhouse_sqlalchemy.sql.ddl import ttl_delete, ttl_to_disk, ttl_to_volume

    class TestTable(self.base):
        date = Column(types.Date, primary_key=True)
        x = Column(types.Int32)

        __table_args__ = (
            engines.MergeTree(
                ttl=[
                    ttl_delete(date + func.toIntervalDay(1)),
                    ttl_to_disk(date + func.toIntervalDay(1), 'hdd'),
                    ttl_to_volume(date + func.toIntervalDay(1), 'slow'),
                ],
            ),
        )

[xzkostyan]

Good job. Please fix flake8 and we'll merge this.

I don't know why travis do not post checks in PR's anymore.

[xzkostyan]

It would be great if reflection of TTL clause will be supported as well.

CREATE TABLE test_table (date Date, x Int32) ENGINE = MergeTree() ORDER BY tuple() TTL date + toIntervalDay(1);

CREATE TABLE test_table
(
    `date` Date,
    `x` Int32
)
ENGINE = MergeTree()
ORDER BY tuple()
TTL date + toIntervalDay(1)

Ok.

0 rows in set. Elapsed: 0.007 sec. 

select * from system.tables where name = 'test_table';

SELECT *
FROM system.tables
WHERE name = 'test_table'

Row 1:
──────
database:                   default
name:                       test_table
uuid:                       00000000-0000-0000-0000-000000000000
engine:                     MergeTree
is_temporary:               0
data_paths:                 ['/.../data/default/test_table/']
metadata_path:              /.../metadata/default/test_table.sql
metadata_modification_time: 2020-11-29 15:47:07
dependencies_database:      []
dependencies_table:         []
create_table_query:         CREATE TABLE default.test_table (`date` Date, `x` Int32) ENGINE = MergeTree() ORDER BY tuple() TTL date + toIntervalDay(1) SETTINGS index_granularity = 8192
engine_full:                MergeTree() ORDER BY tuple() TTL date + toIntervalDay(1) SETTINGS index_granularity = 8192
partition_key:              
sorting_key:                
primary_key:                
sampling_key:               
storage_policy:             default
total_rows:                 0
total_bytes:                0
lifetime_rows:              ᴺᵁᴸᴸ
lifetime_bytes:             ᴺᵁᴸᴸ

1 rows in set. Elapsed: 0.067 sec. 

Few highlights for it:

• add engine_full parameter to method clickhouse_sqlalchemy.engines.mergetree.MergeTree._reflect_merge_tree signature;
• check for ttl in engine_full;
• parse TTL clause or simply wrap it in sqlalchemy.text();
• add it to the engine constructor arguments rv.

[coveralls]

Coverage increased (+0.05%) to 95.586% when pulling 9b625e2 on aamalev:ttl into 3c7277d on xzkostyan:master.