MySQL Bugs: #91386: Index for group-by is not used with primary key for SELECT COUNT(DISTINCT a)

Bug #91386	Index for group-by is not used with primary key for SELECT COUNT(DISTINCT a)
Submitted:	24 Jun 2018 0:30	Modified:	29 Jun 2018 12:23
Reporter:	monty solomon	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Optimizer	Severity:	S4 (Feature request)
Version:	5.7.18	OS:	Any
Assigned to:		CPU Architecture:	Any

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File:	Maximum allowed size is 50MB.
Description:
Privacy:

If the data you need to attach is more than 50MB, you should create a compressed archive of the data, split it to 50MB chunks, and upload each of them as a separate attachment.

To split a large file:

On *nix platforms use the split command e.g. split -b 50MB <my_large_archive> <my_split_archive_prefix>
On windows use WinZip or a similar utility to split the large file

optimizer trace with index a present

Attachment: trace_with_index_a.txt (text/plain), 5.71 KiB.

optimizer trace without index a

Attachment: trace_without_index_a.txt (text/plain), 4.12 KiB.