Clickhouse prewhere demonstration

prewhere.sql

SELECT version()
┌─version()─┐
│ 1.1.54380 │
└───────────┘

SELECT *
FROM system.settings 
WHERE name LIKE '%prewh%';

┌─name──────────────────────┬─value─┬─changed─┬─description───────────────────────────────────────────────────────────────────────┐
│ optimize_move_to_prewhere │ 1     │       0 │ Allows disabling WHERE to PREWHERE optimization in SELECT queries from MergeTree. │
└───────────────────────────┴───────┴─────────┴───────────────────────────────────────────────────────────────────────────────────┘


DROP TABLE IF EXISTS prewhere_test;

CREATE TABLE prewhere_test
(
    number UInt64, 
    date Date DEFAULT '2018-05-14', 
    column001 String DEFAULT concat('abc', toString(rand(1)), 'def'), 
    column002 String DEFAULT if(number = 500, 'look_for_me_please', ''), 
    hugecolumn String DEFAULT arrayStringConcat( arrayMap(x -> concat('abc', toString(rand64(x)), 'def'),  range(500)) , 'sadfasdfasdf')

)
ENGINE = MergeTree(date, (number,column001,column002), 8192);

insert into prewhere_test(number) select * from numbers(1000);

set max_bytes_to_read = 100000;
-- prewhere works perfect
select * from prewhere_test prewhere column002 = 'look_for_me_please' order by number;

-- where condition should be optimized to prewhere, but it don't if the column is the part of PK.
select * from prewhere_test where column002 = 'look_for_me_please' order by number;