Premier League Predictor: Astro — Chapter 3, Exercise 2
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TASK
Explain why the add-team route looks up an existing team by name
before creating a new one, and describe a real scenario where
skipping that lookup would create a duplicate teams row for the same
real club.

SOLUTION

Per Chapter 2's own design, a teams row is meant to represent one
real football club permanently, regardless of which seasons it
happens to compete in. A club that gets relegated doesn't stop
existing — its teams row should simply stop having a season_teams
row for the seasons it isn't competing in, and gain a new one again
if it's later promoted back up.

If the add-team route always ran a plain INSERT INTO teams without
first checking whether a team with that name already exists, every
single promotion of a previously-tracked club would create a brand
new, second teams row for the exact same real club, rather than
reusing its original one.

Concrete scenario: Leicester City is tracked as teams.id = 7 during
the 2023/24 season, then gets relegated and has no season_teams row
for 2024/25. When Leicester City is promoted back up for the 2026/27
season and an admin adds "Leicester City" to that season, skipping
the name lookup would INSERT a brand new row — say teams.id = 41 —
for the same real club. The app would now have two separate team
identities for one real team: historical predictions and results tied
to id 7 would never connect to the club's new appearances tied to id
41, silently splitting one club's own history into two disconnected
records.

The WHERE name = ? lookup prevents exactly this: it finds the
original teams.id = 7 row and reuses it, so the club's full history —
past and present seasons alike — stays attached to one single,
consistent team identity.

WHY THIS WORKS AS AN ANSWER
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It explains the real invariant the lookup protects (one permanent
identity per real club) and gives a concrete, numbered example
showing exactly how skipping the lookup would fracture a real club's
own history across two disconnected rows.