add inserted on column for clickhouse - clickhouse

Question

with other databases, you would ad an inserted_on column to a create table with query with inserted_on DateTime DEFAULT now().
However it seems that clickhouse evaluates that column at every query; I am getting the current time every time.
table structure
create table main.contracts(
bk_number UInt64,
bk_timestamp DateTime,
bk_hash String,
address String,
inserted_on DateTime DEFAULT now()
)
ENGINE = MergeTree
PARTITION BY toYYYYMM(bk_timestamp)
ORDER BY (bk_number, bk_timestamp);

Answer 1

I re-created your scenario and it works for me with no problems.
Table Structure:
create table contracts(
bk_number UInt64,
bk_timestamp DateTime,
inserted_on DateTime DEFAULT now()
)
ENGINE = MergeTree
PARTITION BY toYYYYMM(bk_timestamp)
ORDER BY (bk_number, bk_timestamp);
Insert Queries:
INSERT INTO contracts (bk_number,bk_timestamp) VALUES (123,'2023-02-14 01:00:00');
INSERT INTO contracts (bk_number,bk_timestamp) VALUES (456,'2023-02-14 02:00:00');
INSERT INTO contracts (bk_number,bk_timestamp) VALUES (789,'2023-02-14 03:00:00');
INSERT INTO contracts (bk_number,bk_timestamp) VALUES (101,'2023-02-14 04:00:00');
INSERT INTO contracts (bk_number,bk_timestamp) VALUES (102,'2023-02-14 05:00:00');
INSERT INTO contracts (bk_number,bk_timestamp) VALUES (103,'2023-02-14 06:00:00');
INSERT INTO contracts (bk_number,bk_timestamp) VALUES (104,'2023-02-14 07:00:00');
The Result:
SELECT NOW();
┌───────────────now()─┐
│ 2023-02-15 04:17:51 │
└─────────────────────┘
SELECT * FROM contracts;
┌─bk_number─┬────────bk_timestamp─┬─────────inserted_on─┐
│ 101 │ 2023-02-14 04:00:00 │ 2023-02-15 04:08:39 │
│ 102 │ 2023-02-14 05:00:00 │ 2023-02-15 04:08:39 │
│ 103 │ 2023-02-14 06:00:00 │ 2023-02-15 04:08:39 │
│ 104 │ 2023-02-14 07:00:00 │ 2023-02-15 04:09:30 │
│ 123 │ 2023-02-14 01:00:00 │ 2023-02-15 04:07:33 │
│ 456 │ 2023-02-14 02:00:00 │ 2023-02-15 04:08:39 │
│ 789 │ 2023-02-14 03:00:00 │ 2023-02-15 04:08:39 │
└───────────┴─────────────────────┴─────────────────────┘
SELECT * FROM contracts WHERE bk_number = 123;
┌─bk_number─┬────────bk_timestamp─┬─────────inserted_on─┐
│ 123 │ 2023-02-14 01:00:00 │ 2023-02-15 04:07:33 │
└───────────┴─────────────────────┴─────────────────────┘
Suggestion:
If the table is not too big I would recommend running OPTIMIZE TABLE once.
Check what OPTIMIZE does over here -
Clickhouse Docs/Optimize