docs(mimic-iv-ed): sample query for early prescription starttimes

Illustrate hosp.prescriptions vs edstays.intime joins for #1910.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: Chessing234

mimic-iv-ed/concepts/prescriptions_near_edstay.sql

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+-- Flag hospital prescriptions near an ED stay whose starttime precedes intime.
+-- Join is intentionally loose (subject_id + hadm_id) — same caveat as #1910.
+
+SELECT
+  e.stay_id,
+  e.intime,
+  e.outtime,
+  pr.starttime,
+  pr.stoptime,
+  pr.drug
+FROM ed.edstays AS e
+INNER JOIN hosp.prescriptions AS pr
+  ON e.subject_id = pr.subject_id
+ AND e.hadm_id IS NOT DISTINCT FROM pr.hadm_id
+WHERE pr.starttime < e.intime
+  AND pr.starttime >= e.intime - INTERVAL '6 hours'
+ORDER BY e.stay_id, pr.starttime
+LIMIT 100;