Data Explorer (SEDE)

It is a bit of juggling by generating a dynamic query (using the PIVOT statement fom TSQL) in a variable and then run that sql with the EXEC statement

That allows you to give in a single field a comma separated list of tags you want to see those percentage for

the first column either needs to be a date or a number and its values go on x-axis, all other columns go as Y-values

That x hours ago is also shown in the help on the first FAQ item, last sentence.

and you can see the last update date here: i.sstatic.net/TnT1p.png

You might like the format function: docs.microsoft.com/en-us/sql/t-sql/functions/… it allows you to format the values from several types into a varchar using the .Net composite string formatting options. Select format(getdate(), 'yyyy-MM' ) gives you 2018-08 in one go.

@Martin to group by day can be achieved by casting (or converting) a datetime to a date type, so group by cast(creationdate as date). The date type doesn't allow for a time component so it will simply drop that from the datetime values. For month there isn't such trick, but you don't need to convert to str and concat. A group by yesr(creationdate), month(creationdate) will work.

So looking there, I should have added ClosedDate and Tags to that list.

@Martin yes, but the tags field is later added to be populated as well which is reflected in the Database schema answer (the superscript 1 are used to indicate that)

The PostsWithDeleted table is useful for that. However, for deleted questions only some information is kept - according to this answer it is Id, PostTypeId, ParentId, CreationDate, DeletionDate, Score.

This post is very likely to be useful for anybody working with SEDE: Database schema documentation for the public data dump and SEDE.

Not if you apply the technique with JSON_VALUE I applied here: data.stackexchange.com/stackoverflow/query/873421