[Bug]fix the crash of checksum task #3735

[marising]

1. the table include key column of double/float type
2. when run checksum task, will use all of key columns to compare
3. schema.column(idx) of double/float type is NULL

#3735

[morningman]

This CL looks good to me.
But I had a question in your issue: #3735, that why key columns include float or double.
We don't support using float or double column as key column.

[marising]

It's very confusing for me，doris does not support the key column as double or float，but I've met twice.

1. I test alter table add double key column
   MySQL [checksum]> alter table catalog_sales modify column cs_sales_price double KEY null after cs_item_sk;
   ERROR 1064 (HY000): Float or double can not used as a key, use decimal instead.

2. The table of customer
   alter table add column xxx double key null after xxx，but no error message and execute success!

MySQL [search]> desc xxx_sku_AB;
+--------------+-------------+------+-------+---------+-----------+
| Field | Type | Null | Key | Default | Extra |
+--------------+-------------+------+-------+---------+-----------+
...
| price | DOUBLE | Yes | true | N/A | |
....
+--------------+-------------+------+-------+---------+-----------

[imay]

2. The table of customer
alter table add column xxx double key null after xxx，but no error message and execute success!

@marising
Should create an issue to fix it.

[morningman]

2. The table of customer
alter table add column xxx double key null after xxx，but no error message and execute success!

I guess the table customer is a DUPLICATE KEY table, right? So that the key in alter table stmt is not exactly a key column, but just a sort column.

I think its ok to allow a float type column to be a sort column in DUPLICATE KEY table.

@imay , is that right?

[imay]

@morningman I'm not sure about it either. However I think it is OK to make double/float column as a sort key.

[marising]

Aggregate Key, not Duplicate Key @morningman

CREATE TABLE xxx_sku_AB (
......
price double NULL COMMENT "",
......
) ENGINE=OLAP
...
AGGREGATE KEY(..., price, ...)
...

[marising]

2. The table of customer
   alter table add column xxx double key null after xxx，but no error message and execute success!

@marising
Should create an issue to fix it.

I can't reproduce this problem in the online cluster of customer, and the time for adding columns is a little long audit.log be cleaned up, I will pay attention to this problem

[imay]

LGTM

[morningman]

hi @marising , if you finished this PR, please let me know, thank u.

[marising]

@morningman Ok，I'll tell you, if our internal review passes.

[morningman]

LGTM