fix: 추천 검색어 동적 임계값 필터링 복원

- SQL GREATEST()로 동적 임계값 적용
- MAX(count) * 1% 또는 최소 10회 중 더 큰 값 사용
- Prefix, 초성, 인기 검색어 모두 필터링 적용
- 데이터가 적을 때도 오타 필터링 가능

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/services/suggestions/index.js

@@ -15,8 +15,8 @@ const inko = new Inko();
 const CONFIG = {
   // 추천 검색어 최소 검색 횟수 비율 (최대 대비)
   MIN_COUNT_RATIO: 0.01,
-  // 최소 임계값 (데이터 적을 때)
+  // 최소 임계값 (데이터 적을 때 오타 방지)
-  MIN_COUNT_FLOOR: 5,
+  MIN_COUNT_FLOOR: 10,
   // Redis 키 prefix
   REDIS_PREFIX: 'suggest:',
   // 캐시 TTL (초)
@@ -24,7 +24,6 @@ const CONFIG = {
     PREFIX: 3600,      // prefix 검색: 1시간
     BIGRAM: 86400,     // bi-gram: 24시간
     POPULAR: 600,      // 인기 검색어: 10분
-    MAX_COUNT: 3600,   // 최대 횟수: 1시간
   },
 };
 
@@ -208,6 +207,7 @@ export class SuggestionService {
 
   /**
    * Prefix 매칭
+   * - GREATEST()로 동적 임계값 적용: MAX(count) * 1% 또는 최소 10 중 더 큰 값
    */
   async getPrefixSuggestions(prefix, koreanPrefix, limit) {
     try {
@@ -216,19 +216,21 @@ export class SuggestionService {
       if (koreanPrefix) {
         // 영어 + 한글 변환 둘 다 검색
         [rows] = await this.db.query(
-          `SELECT query, count FROM suggestion_queries
+          `SELECT query FROM suggestion_queries
-           WHERE query LIKE ? OR query LIKE ?
+           WHERE (query LIKE ? OR query LIKE ?)
+             AND count >= GREATEST((SELECT MAX(count) * ? FROM suggestion_queries), ?)
            ORDER BY count DESC, last_searched_at DESC
            LIMIT ?`,
-          [`${prefix}%`, `${koreanPrefix}%`, limit]
+          [`${prefix}%`, `${koreanPrefix}%`, CONFIG.MIN_COUNT_RATIO, CONFIG.MIN_COUNT_FLOOR, limit]
         );
       } else {
         [rows] = await this.db.query(
-          `SELECT query, count FROM suggestion_queries
+          `SELECT query FROM suggestion_queries
            WHERE query LIKE ?
+             AND count >= GREATEST((SELECT MAX(count) * ? FROM suggestion_queries), ?)
            ORDER BY count DESC, last_searched_at DESC
            LIMIT ?`,
-          [`${prefix}%`, limit]
+          [`${prefix}%`, CONFIG.MIN_COUNT_RATIO, CONFIG.MIN_COUNT_FLOOR, limit]
         );
       }
 
@@ -241,15 +243,17 @@ export class SuggestionService {
 
   /**
    * 초성 검색
+   * - GREATEST()로 동적 임계값 적용
    */
   async getChosungSuggestions(chosung, limit) {
     try {
       const [rows] = await this.db.query(
-        `SELECT word, count FROM suggestion_chosung
+        `SELECT word FROM suggestion_chosung
          WHERE chosung LIKE ?
+           AND count >= GREATEST((SELECT MAX(count) * ? FROM suggestion_chosung), ?)
          ORDER BY count DESC
          LIMIT ?`,
-        [`${chosung}%`, limit]
+        [`${chosung}%`, CONFIG.MIN_COUNT_RATIO, CONFIG.MIN_COUNT_FLOOR, limit]
       );
 
       return rows.map(r => r.word);
@@ -261,6 +265,7 @@ export class SuggestionService {
 
   /**
    * 인기 검색어 조회
+   * - GREATEST()로 동적 임계값 적용
    */
   async getPopularQueries(limit = 10) {
     try {
@@ -272,12 +277,13 @@ export class SuggestionService {
         return JSON.parse(cached);
       }
 
-      // DB 조회
+      // DB 조회 (동적 임계값 이상만)
       const [rows] = await this.db.query(
-        `SELECT query, count FROM suggestion_queries
+        `SELECT query FROM suggestion_queries
+         WHERE count >= GREATEST((SELECT MAX(count) * ? FROM suggestion_queries), ?)
          ORDER BY count DESC
          LIMIT ?`,
-        [limit]
+        [CONFIG.MIN_COUNT_RATIO, CONFIG.MIN_COUNT_FLOOR, limit]
       );
 
       const result = rows.map(r => r.query);