PeopleSoft, under deadline.
Hundreds of tables, duplicate field names, no schema visualisation, and a date. Then a rebuild onto a platform the team can actually report from.
I learned the PeopleSoft query editor in under 24 hours for a high-pressure project: hundreds of tables, the same field name appearing across several of them, no schema visualisation, and the institutional knowledge living in people rather than writing. Trial and error, against a date.
The queries I was working from had been built years earlier and had done their job well. But compliance criteria had moved since then, so once I could read them properly, I went back through the core ones and tested them line by line against the current standard.
Legacy reporting doesn't fail loudly. It just quietly stops matching a standard that moved.
Read it without a map
Hundreds of tables, duplicate field names, nothing visualised, documentation living in people. Under 24 hours, because the project was not going to wait for me to get comfortable.
Run it against the standard as it stands now
Each core query, line by line, against current compliance criteria, not against what it returned last year, and not against what it was built to return. Most of them held. The interesting ones are the few that no longer reconciled.
Trace before you touch
A result that disagrees with the standard has two possible causes, and they need opposite fixes: the query drifted, or the criteria moved underneath it. Rewriting before you know which produces a query that is confidently wrong in a new way.
Rebuild somewhere still supported
The ones that needed it were rebuilt in SAP Business Objects, aggregating the data more efficiently on the way across, aligned to current state criteria, and re-runnable by anyone. A query only I can operate has the same expiry date as a system only I can administer.
The team now reports from an actively supported platform, on queries anyone can re-run and check. The reputation that followed is the part I'd point at: when something is manual, repetitive, or due for a rebuild, I'm the person the team brings it to, and the answer is usually a tool rather than more hours.
The word my colleagues use is "Swiss Army knife." It isn't mine and I wouldn't have picked it, but it describes the job accurately: people bring me the thing nobody knows how to do yet. See where that habit goes on its own time.