通過csv文件提供的數據庫表內容：

links.csv的格式：

movies.csv格式，一個movie可以有多種風格(genres)，通過|分隔：

ratings.csv:

用戶給movie打得分：

tags.csv：movie的標簽

練習一：

列出四張表的總記錄數：

select 'links' as "table name", count(1) as "row count" from "MOVIELENS"."public.aa.movielens.hdb::data.LINKS" union all select 'movies' as "table name", count(1) as "row count" from "MOVIELENS"."public.aa.movielens.hdb::data.MOVIES" union all select 'ratings' as "table name", count(1) as "row count" from "MOVIELENS"."public.aa.movielens.hdb::data.RATINGS" union all select 'tags' as "table name", count(1) as "row count" from "MOVIELENS"."public.aa.movielens.hdb::data.TAGS";

執行結果：

練習2：計算總共9125部電影，一共包含多少藝術類別？

DO BEGINDECLARE genreArray NVARCHAR(255) ARRAY;DECLARE tmp NVARCHAR(255);DECLARE idx INTEGER;DECLARE sep NVARCHAR(1) := '|';DECLARE CURSOR cur FOR SELECT DISTINCT "GENRES" FROM "MOVIELENS"."public.aa.movielens.hdb::data.MOVIES";DECLARE genres NVARCHAR (255) := '';idx := 1;FOR cur_row AS cur() DOSELECT cur_row."GENRES" INTO genres FROM DUMMY;tmp := :genres;WHILE LOCATE(:tmp,:sep) > 0 DOgenreArray[:idx] := SUBSTR_BEFORE(:tmp,:sep);tmp := SUBSTR_AFTER(:tmp,:sep);idx := :idx + 1;END WHILE;genreArray[:idx] := :tmp;END FOR;genreList = UNNEST(:genreArray) AS ("GENRE");SELECT "GENRE" FROM :genreList GROUP BY "GENRE"; END;

執行結果，總共包含18種：

練習3：計算每種藝術類別總共包含多少部電影：

DO BEGINDECLARE genreArray NVARCHAR(255) ARRAY;DECLARE tmp NVARCHAR(255);DECLARE idx INTEGER;DECLARE sep NVARCHAR(1) := '|';DECLARE CURSOR cur FOR SELECT DISTINCT "GENRES" FROM "MOVIELENS"."public.aa.movielens.hdb::data.MOVIES";DECLARE genres NVARCHAR (255) := '';idx := 1;FOR cur_row AS cur() DOSELECT cur_row."GENRES" INTO genres FROM DUMMY;tmp := :genres;WHILE LOCATE(:tmp,:sep) > 0 DOgenreArray[:idx] := SUBSTR_BEFORE(:tmp,:sep);tmp := SUBSTR_AFTER(:tmp,:sep);idx := :idx + 1;END WHILE;genreArray[:idx] := :tmp;END FOR;genreList = UNNEST(:genreArray) AS ("GENRE");SELECT "GENRE", count(1) FROM :genreList GROUP BY "GENRE"; END;

練習4：列出每部電影包含的風格數目：

SELECT"MOVIEID", "TITLE", OCCURRENCES_REGEXPR('[|]' IN GENRES) + 1 "GENRE_COUNT", "GENRES" FROM "MOVIELENS"."public.aa.movielens.hdb::data.MOVIES" ORDER BY "GENRE_COUNT" ASC;

練習5：羅列出每部電影的風格分布情況

SELECT"GENRE_COUNT", COUNT(1) FROM (SELECTOCCURRENCES_REGEXPR('[|]' IN "GENRES") + 1 "GENRE_COUNT"FROM "MOVIELENS"."public.aa.movielens.hdb::data.MOVIES" ) GROUP BY "GENRE_COUNT" ORDER BY "GENRE_COUNT";

比如至少擁有1個風格的電影，有2793部，2個風格的電影有3039部，等等。

練習6：計算movie的rating分布情況

SELECT DISTINCTMIN("RATING_COUNT") OVER( ) AS "MIN",MAX("RATING_COUNT") OVER( ) AS "MAX",AVG("RATING_COUNT") OVER( ) AS "AVG",SUM("RATING_COUNT") OVER( ) AS "SUM",MEDIAN("RATING_COUNT") OVER( ) AS "MEDIAN",STDDEV("RATING_COUNT") OVER( ) AS "STDDEV",COUNT(*) OVER( ) AS "CATEGORY_COUNT" FROM (SELECT "MOVIEID", COUNT(1) as "RATING_COUNT"FROM "MOVIELENS"."public.aa.movielens.hdb::data.RATINGS"GROUP BY "MOVIEID" ) GROUP BY "RATING_COUNT";

明細情況：

SELECT "RATING_COUNT", COUNT(1) as "MOVIE_COUNT" FROM (SELECT "MOVIEID", COUNT(1) as "RATING_COUNT"FROM "MOVIELENS"."public.aa.movielens.hdb::data.RATINGS"GROUP BY "MOVIEID" ) GROUP BY "RATING_COUNT" ORDER BY "RATING_COUNT" asc;

比如有397部電影的用戶投票數為5票

練習7：統計用戶投票情況

SELECT "RATING_COUNT", COUNT(1) as "USER_COUNT" FROM (SELECT "USERID", COUNT(1) as "RATING_COUNT"FROM "MOVIELENS"."public.aa.movielens.hdb::data.RATINGS"GROUP BY "USERID" ) GROUP BY "RATING_COUNT" ORDER BY 1 DESC;

有一位用戶投了2391票，一位用戶投了1868票：

練習8：統計用戶投票得分情況

SELECT "RATING", COUNT(1) as "RATING_COUNT" FROM "MOVIELENS"."public.aa.movielens.hdb::data.RATINGS" GROUP BY "RATING" ORDER BY 1 DESC;

有15095份用戶投票，打的分數是5分

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