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I can't say that I fully understood what you did, but I think I got the explanation: removed 1+ columns that were part of the index. The index will be updated to not include that column. If...
Answer
#2: Post edited
by
Alexei
·
2020-11-10T06:25:43Z (about 4 years ago)
Removed irrelevant information
#1: Initial revision
by
Alexei
·
2020-11-09T18:58:45Z (about 4 years ago)
I can't say that I fully understood what you did, but I think I got the explanation: - removed 1+ columns that were part of the index. [The index will be updated to not include that column](https://dev.mysql.com/doc/refman/8.0/en/alter-table.html). Uniqueness might be lost since uniqueness was ensured by the initial combination of columns: > If columns are dropped from a table, the columns are also removed from any index of which they are apart. If all columns that make up an index are dropped, the index is dropped as well. - [all secondary indexes include the PK columns](https://dev.mysql.com/doc/refman/8.0/en/innodb-index-types.html#:~:text=All%20indexes%20other%20than%20the,specified%20for%20the%20secondary%20index.). Not really sure, but dropping all the non-PK columns from the indexes you can get to your strange situation when the indexes are basically the same as the PK.