perf: 월 범위 세션 선필터링으로 월간 통계 쿼리 성능 개선

src/main/java/com/gpt/geumpumtabackend/statistics/repository/StatisticsRepository.java

@@ -156,97 +156,117 @@ WeeklyStatistics getWeeklyStatistics(
     );
 
     @Query(value = """
-        WITH RECURSIVE
-        bounds AS (
-          SELECT
-            :monthStart AS start_at,
-            DATE_ADD(LAST_DAY(:monthStart), INTERVAL 1 DAY) AS end_at,
-            TIMESTAMPDIFF(
-              DAY, :monthStart,
-              DATE_ADD(LAST_DAY(:monthStart), INTERVAL 1 DAY)
-            ) AS days_cnt
-        ),
-        /* 월 전체 일자를 day_idx=0..(days_cnt-1)로 생성 */
-        days AS (
-          SELECT
-            0 AS day_idx,
-            b.start_at AS day_start,
-            LEAST(DATE_ADD(b.start_at, INTERVAL 1 DAY), b.end_at) AS day_end
-          FROM bounds b
-          UNION ALL
-          SELECT
-            d.day_idx + 1,
-            DATE_ADD(d.day_start, INTERVAL 1 DAY),
-            LEAST(DATE_ADD(d.day_start, INTERVAL 2 DAY), b.end_at)
-          FROM days d
-          JOIN bounds b
-            ON d.day_end < b.end_at
-        ),
-        /* 일자별 공부 총합(ms) */
-        per_day AS (
-          SELECT
-            d.day_idx,
-            CAST(
-              COALESCE(
-                SUM(
-                  GREATEST(
-                    0,
-                    TIMESTAMPDIFF(
-                      MICROSECOND,
-                      GREATEST(s.start_time, d.day_start),
-                      LEAST(COALESCE(s.end_time, d.day_end), d.day_end)
-                    ) / 1000
-                  )
-                ), 0
-              ) AS SIGNED
-            ) AS day_millis
-          FROM days d
-          LEFT JOIN study_session s
-            ON s.user_id    = :userId
-           AND s.start_time < d.day_end
-           AND s.end_time   > d.day_start
-          GROUP BY d.day_idx
-        ),
-        flags AS (
-          SELECT
-            day_idx,
-            day_millis,
-            CASE WHEN day_millis > 0 THEN 1 ELSE 0 END AS has_study
-          FROM per_day
-        ),
-        breaks AS (
-          /* 0(공부 안 한 날)을 경계로 그룹을 나눠 연속 구간 식별 */
-          SELECT
-            day_idx,
-            day_millis,
-            has_study,
-            SUM(CASE WHEN has_study = 0 THEN 1 ELSE 0 END)
-              OVER (ORDER BY day_idx) AS zero_grp
-          FROM flags
-        ),
-        streaks AS (
-          SELECT zero_grp, COUNT(*) AS streak_len
-          FROM breaks
-          WHERE has_study = 1
-          GROUP BY zero_grp
-        )
-        SELECT
-          /* 총 공부시간(ms) */
-          CAST(COALESCE((SELECT SUM(day_millis) FROM per_day), 0) AS SIGNED) AS totalMonthMillis,
-          /* 월 일수로 나눈 일일 평균(ms; 소수 버림) */
-          CAST( (COALESCE((SELECT SUM(day_millis) FROM per_day), 0)
-                / NULLIF((SELECT days_cnt FROM bounds), 0)) AS SIGNED)        AS averageDailyMillis,
-          /* 최장 연속 공부 일수 */
-          COALESCE((SELECT MAX(streak_len) FROM streaks), 0)                  AS maxConsecutiveStudyDays,
-          /* 이번 달 공부 일수(>0ms) */
-          (SELECT COUNT(*) FROM per_day WHERE day_millis > 0)                 AS studiedDays
-        """, nativeQuery = true)
+    WITH RECURSIVE
+    bounds AS (
+      SELECT
+        :monthStart AS start_at,
+        DATE_ADD(LAST_DAY(:monthStart), INTERVAL 1 DAY) AS end_at,
+        TIMESTAMPDIFF(
+          DAY, :monthStart,
+          DATE_ADD(LAST_DAY(:monthStart), INTERVAL 1 DAY)
+        ) AS days_cnt
+    ),
+
+    /* (개선) 이번 달과 겹치는 "완료된" 세션만 먼저 선필터링 */
+    filtered_sessions AS (
+      SELECT s.user_id, s.start_time, s.end_time
+      FROM study_session s
+      JOIN bounds b
+        ON s.user_id = :userId
+       AND s.end_time IS NOT NULL                 /* 진행 중 세션 제외 (의도 유지) */
+       AND s.start_time < b.end_at                /* 달 끝보다 먼저 시작 */
+       AND s.end_time   > b.start_at              /* 달 시작보다 나중에 끝 */
+    ),
+
+    /* 월 전체 일자를 day_idx=0..(days_cnt-1)로 생성 */
+    days AS (
+      SELECT
+        0 AS day_idx,
+        b.start_at AS day_start,
+        LEAST(DATE_ADD(b.start_at, INTERVAL 1 DAY), b.end_at) AS day_end
+      FROM bounds b
+      UNION ALL
+      SELECT
+        d.day_idx + 1,
+        DATE_ADD(d.day_start, INTERVAL 1 DAY),
+        LEAST(DATE_ADD(d.day_start, INTERVAL 2 DAY), b.end_at)
+      FROM days d
+      JOIN bounds b
+        ON d.day_end < b.end_at
+    ),
+
+    /* 일자별 공부 총합(ms) */
+    per_day AS (
+      SELECT
+        d.day_idx,
+        CAST(
+          COALESCE(
+            SUM(
+              GREATEST(
+                0,
+                TIMESTAMPDIFF(
+                  MICROSECOND,
+                  GREATEST(s.start_time, d.day_start),
+                  LEAST(s.end_time, d.day_end)
+                ) / 1000
+              )
+            ), 0
+          ) AS SIGNED
+        ) AS day_millis
+      FROM days d
+      LEFT JOIN filtered_sessions s
+        ON s.start_time < d.day_end
+       AND s.end_time   > d.day_start
+      GROUP BY d.day_idx
+    ),
+
+    flags AS (
+      SELECT
+        day_idx,
+        day_millis,
+        CASE WHEN day_millis > 0 THEN 1 ELSE 0 END AS has_study
+      FROM per_day
+    ),
+
+    breaks AS (
+      /* 0(공부 안 한 날)을 경계로 그룹을 나눠 연속 구간 식별 */
+      SELECT
+        day_idx,
+        day_millis,
+        has_study,
+        SUM(CASE WHEN has_study = 0 THEN 1 ELSE 0 END)
+          OVER (ORDER BY day_idx) AS zero_grp
+      FROM flags
+    ),
+
+    streaks AS (
+      SELECT zero_grp, COUNT(*) AS streak_len
+      FROM breaks
+      WHERE has_study = 1
+      GROUP BY zero_grp
+    )
+
+    SELECT
+      /* 총 공부시간(ms) */
+      CAST(COALESCE((SELECT SUM(day_millis) FROM per_day), 0) AS SIGNED) AS totalMonthMillis,
+
+      /* 월 일수로 나눈 일일 평균(ms; 소수 버림) */
+      CAST( (COALESCE((SELECT SUM(day_millis) FROM per_day), 0)
+            / NULLIF((SELECT days_cnt FROM bounds), 0)) AS SIGNED)        AS averageDailyMillis,
+
+      /* 최장 연속 공부 일수 */
+      COALESCE((SELECT MAX(streak_len) FROM streaks), 0)                  AS maxConsecutiveStudyDays,
+
+      /* 이번 달 공부 일수(>0ms) */
+      (SELECT COUNT(*) FROM per_day WHERE day_millis > 0)                 AS studiedDays
+    """, nativeQuery = true)
     MonthlyStatistics getMonthlyStatistics(
             @Param("monthStart") LocalDateTime monthStart, // 해당 월 1일 00:00
             @Param("userId") Long userId
     );
 
 
+
     @Query(value = """
     WITH RECURSIVE
     bounds AS (