sqlite: wide v. long performance - performance

Question

I'm considering whether I should format a table in my sqlite database in "wide or "long" format. Examples of these formats are included at the end of the question.
I anticipate that the majority of my requests will be of the form:
SELECT * FROM table
WHERE
series in (series1, series100);
or the analog for selecting by columns in wide format.
I also anticipate that there will be a large number of columns, even enough to need to increase the column limit.
Are there any general guidelines for selecting a table layout that will optimize query performance for this sort of case?
(Examples of each)
"Wide" format:
| date | series1 | series2 | ... | seriesN |
| ---------- | ------- | ------- | ---- | ------- |
| "1/1/1900" | 15 | 24 | 43 | 23 |
| "1/2/1900" | 15 | null | null | 23 |
| ... | 15 | null | null | 23 |
| "1/2/2019" | 12 | 12 | 4 | null |
"Long" format:
| date | series | value |
| ---------- | ------- | ----- |
| "1/1/1900" | series1 | 15 |
| "1/2/1900" | series1 | 15 |
| ... | series1 | 43 |
| "1/2/2019" | series1 | 12 |
| "1/1/1900" | series2 | 15 |
| "1/2/1900" | series2 | 15 |
| ... | series2 | 43 |
| "1/2/2019" | series2 | 12 |
| ... | ... | ... |
| "1/1/1900" | seriesN | 15 |
| "1/2/1900" | seriesN | 15 |
| ... | seriesN | 43 |
| "1/2/2019" | seriesN | 12 |

Answer 1

The "long" format is the preferred way to go here, for so many reasons. First, if you use the "wide" format and there is ever a need to add more series, then you would have to add new columns to the database table. While this is not too much of a hassle, in general once you put a schema into production, you want to avoid further schema changes.
Second, the "long" format makes reporting and querying much easier. For example, suppose you wanted to get a count of rows/data points for each series. Then you would only need something like:
SELECT series, COUNT(*) AS cnt
FROM yourTable
GROUP BY series;
To get this report with the "wide" format, you would need a lot more code, and it would be as verbose as your sample data above.
The thing to keep in mind here is that SQL databases are built to operate on sets of records (read: across rows). They can also process things column wise, but they are not generally setup to do this.