Re: MySql 5.7.3 m13 deadly slow - config issue?

[Øystein Grøvlen]

Hi,

MySQL will not use index if a type conversion is needed. VARCHAR columns with different character set or collation is regarded as being of different type.

One reason for this is that two strings that may be considered equal with one collation may not be considered equal with another collation (e.g., case-sensitive versus case-insensitive). Hence, within an index, from the point of view of a different collation, all rows with matching strings may not be located together, and it will not be possible to use an index look-up to find matching rows.

I am not very familiar with what changes have been done to character sets over the years, so I am not able to tell why you see different behavior in MySQL 5.7 compared to an earlier version.

Øystein Grøvlen,
Senior Principal Software Engineer,
MySQL Group, Oracle,
Trondheim, Norway