Preface when there is rain neither sun nor moon, the people actually do not think so. Perhaps there are seasonal climate not to be cold rain, let the sun or the cool side. Has the rain the night is otherwise a moonlit night no flavor. Some
Preface
when there is rain neither sun nor moon, the people actually do not think so.
Perhaps there are seasonal climate not to be cold rain, let the sun or the cool side.
Has the rain the night is otherwise a moonlit night no flavor.
Sometimes not reminiscent of Li Shangyin “when he cut a total of west window candle, but then when the famous hope of reunion among friends”
In the rain, fom the sky come the silk notes; here, quiet and comfortable.
Presentation
In this page, we will show the homework of the course of the Databases Technology in CMU. All of the questions we tested in the postgresql.
This section mainly is to practice the query operation of the SQL, include SQL view, index, etc. We also sure that all the sqls will pass in the mysql, sqlite… , this article also will provide the Chinese version in detail.
中文版
Question Details
In this homework you will have to write SQL queries to answer questions on a movie dataset, about movies and actors. The database contains two tables:
? movies(mid, title, year, num ratings, rating) , Primary key: mid
? play in(mid, name, cast position), Primary key: mid, name
The tables contain the obvious information: which actor played in what movie, at what position; for each movie, we have the title (eg., ’Gone with the wind’), year of production, count of rating reviews it received, and the average score of those ratings (a float in the range 0 to 10, with ’10’ meaning ’excellent’).
We will use Postgres, which is installed in the your own machines.
Question 1: Warm-up queries … … … … … … … … . [5 points]
(a) [2 points] Print all actors in the movie Quantum of Solace, sorted by cast position. Print only their names.
(b) [3 points] Print all movie titles that were released in 2002, with rating larger than 8 and with more than one rating (num ratings > 1).
Question 2: Find the star’s movies … … … … … … . . [5 points]
(a) [5 points] Print movie titles where Sean Connery was the star (i.e. he had position 1 in the cast). Sort the movie titles alphabetically.
Question 3: Popular actors … … … … … … … … . . [15 points]
(a) [8 points] We want to find the actors of the highest quality. We define their quality as the weighted average of the ratings of the movies they have played in (regardless of cast position), using the number of ratings for each movie as the
weight. In other words, we define the quality for a particular actor as
Print the names of the top 5 actors, according to the above metric. Break ties alphabetically.
(b) [7 points] Now we want to find the 5 most popular actors, in terms of number of ratings (regardless of positive or negative popularity). I.e, if actor ‘Smith’ played in 2 movies, with num ratings 10 and 15, then Smith’s popularity is 25 (=10+15). Print the top 5 actor names according to popularity. Again, break ties alphabetically.
Question 4: Most controversial actor … … … … … . [10 points]
(a) [10 points] We want to find the most controversial actor. As a measure of controversy, we define the maximum difference between the ratings of two movies that an actor has played in (regardless of cast position). That is, if actor ‘Smith’ played in a movie that got rating=1.2, and another that got rating=9.5, and all the other movies he played in, obtained scores within that range, then Smith’s contoversy score is 9.5-1.2= 8.3. Print the name of the top-most controversial actor - again, if there is a tie in first place, break it alphabetically.
Question 5: The minions … … … … … … … … … . [20 points]
(a) [20 points] Find the “minions” of Annette Nicole: Print the names of actors who only played in movies with her and never without her. The answer should not contain the name of Annette Nicole. Order the names alphabetically.
Question 6: High productivity … … … … … … … … [5 points]
(a) [5 points] Find the top 2 most productive years (by number of movies produced). Solve ties by preferring chronologically older years, and print only the years.
Question 7: Movies with similar cast … … … … … . [15 points]
(a) [8 points] Print the count of distinct pairs of movies that have at least one actor in common (ignoring cast position). Exclude self-pairs, and mirror-pairs.
(b) [7 points] Print the count of distinct pairs of moves that have at least two actors in common (again, ignoring cast position). Again, exclude self-pairs, and mirror pairs.
Question 8: Skyline query … … … … … … … … … [25 points]
(a) [25 points] We want to find a set of movies that have both high popularity (ie, high num ratings) as well as high quality (rating). No single movie may achieve both - in which case, we want the so-called Skyline query 2 . More specifically, we want all movies that are not “dominated” by any other movie:
Definition of domination : Movie “A” dominates movie “B” if movie “A” wins over movie “B”, on both criteria, or wins on one, and ties on the rest.
Figure 1 gives a pictorial example: the solid dots (’A’, ’D’, ’F’) are not dominated by any other dot, and thus form the skyline. All other dots are dominated by at least one other dot: e.g., dot ’B’ is dominated by dot ’A’, being inside the shaded rectangle that has ’A’ as the upper-right corner.
Figure 1: Illustration of Skyline and domination : ’A’ dominates all points in the shaded rectangle; ’A’, ’D’ and ’F’ form the skyline of this cloud of points.
Given the above description, print the title of all the movies on the skyline, along with the rating and the number of ratings.
Answer
we give the Postgres version in detail, we will see you can tranfer it easily in mysql or sqlite.
Initialization:
<code class=" hljs sql">## <span class="hljs-operator"><span class="hljs-keyword">drop</span> the <span class="hljs-keyword">table</span> <span class="hljs-keyword">if</span> <span class="hljs-keyword">exists</span> <span class="hljs-keyword">drop</span> <span class="hljs-keyword">table</span> <span class="hljs-keyword">if</span> <span class="hljs-keyword">exists</span> movies <span class="hljs-keyword">cascade</span>;</span> <span class="hljs-operator"><span class="hljs-keyword">drop</span> <span class="hljs-keyword">table</span> <span class="hljs-keyword">if</span> <span class="hljs-keyword">exists</span> play_in <span class="hljs-keyword">cascade</span>;</span> ## <span class="hljs-operator"><span class="hljs-keyword">create</span> tables movies <span class="hljs-keyword">and</span> play_in <span class="hljs-keyword">create</span> <span class="hljs-keyword">table</span> movies ( mid <span class="hljs-keyword">integer</span> <span class="hljs-keyword">PRIMARY</span> <span class="hljs-keyword">KEY</span>, title <span class="hljs-keyword">varchar</span>(<span class="hljs-number">200</span>), <span class="hljs-keyword">year</span> <span class="hljs-keyword">integer</span>, num_ratings <span class="hljs-keyword">integer</span>, rating <span class="hljs-keyword">real</span>);</span> <span class="hljs-operator"><span class="hljs-keyword">create</span> <span class="hljs-keyword">table</span> play_in ( mid <span class="hljs-keyword">integer</span> <span class="hljs-keyword">references</span> movies, name <span class="hljs-keyword">varchar</span>(<span class="hljs-number">100</span>), cast_position <span class="hljs-keyword">integer</span>, <span class="hljs-keyword">PRIMARY</span> <span class="hljs-keyword">KEY</span>(mid, name));</span> <span class="hljs-operator"><span class="hljs-keyword">create</span> index mid <span class="hljs-keyword">on</span> movies(mid);</span></code>
Insert Values
Insert into some values into the table movies and play_in,
you will find the datas just in the follow links in my 360 yunFiles:
https://yunpan.cn/cSfLzxQApRXSi password: f3ab
<code class=" hljs rust">## <span class="hljs-keyword">use</span> <span class="hljs-string">"copy"</span> in Postgres \<span class="hljs-keyword">copy</span> movies from <span class="hljs-string">'~/data/movie_processed.dat'</span>; \<span class="hljs-keyword">copy</span> play_in from <span class="hljs-string">'~/data/movie_actor_processed.dat'</span>; ## <span class="hljs-keyword">if</span> you <span class="hljs-keyword">use</span> other databases(mysql, sqlite), you can <span class="hljs-keyword">use</span> the sql statement: <span class="hljs-string">"insert into ... valuse()"</span> </code>
The flowing image show the test infos in my ubuntu os:
Solution 1
<code class=" hljs asciidoc">(a) SELECT name FROM play<span class="hljs-emphasis">_in p, movies m WHERE p.mid = m.mid and m.title=’Quantum of Solace’ ORDER BY p.cast_</span>position; ## (a) Result just like this: <span class="hljs-header">name ------------------------------</span> Daniel Craig Olga Kurylenko Mathieu Amalric Judi Dench Giancarlo Giannini Gemma Arterton Jeffrey Wright David Harbour Jesper Christensen Anatole Taubman Rory Kinnear Tim Pigott-Smith Fernando Guillen-Cuervo Jesus Ochoa Glenn Foster Paul Ritter Simon Kassianides Stana Katic Lucrezia Lante della Rove... Neil Jackson Oona Chaplin (21 rows) (b) SELECT title FROM movies WHERE year = 2002 and rating>8 and num<span class="hljs-emphasis">_ratings>1; </span>## (b) Result just like this: <span class="hljs-header">title ---------------------------------------</span> The Lord of the Rings: The Two Towers Cidade de Deus Mou gaan dou (3 rows) </code>
The flowing image show the test solution 1 infos in my ubuntu os:
Solution 2
<code class=" hljs vbnet"><span class="hljs-keyword">SELECT</span> title <span class="hljs-keyword">from</span> movies m, play_in p <span class="hljs-keyword">WHERE</span> m.<span class="hljs-keyword">mid</span> = p.<span class="hljs-keyword">mid</span> <span class="hljs-keyword">and</span> name = ’Sean Connery’ <span class="hljs-keyword">and</span> cast_position = <span class="hljs-number">1</span> <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span> title; <span class="hljs-preprocessor">## Result just like this:</span> title --------------------------------------- Der Name der Rose Diamonds Are Forever Dr. No Entrapment Finding Forrester First Knight <span class="hljs-keyword">From</span> Russia <span class="hljs-keyword">with</span> Love Goldfinger Never Say Never Again The Hunt <span class="hljs-keyword">for</span> Red October The League <span class="hljs-keyword">of</span> Extraordinary Gentlemen Thunderball You Only Live Twice (<span class="hljs-number">13</span> rows)</code>
The flowing image show the test solution 2 infos in my ubuntu os:
Solution 3
<code class=" hljs sql">(a) <span class="hljs-operator"><span class="hljs-keyword">DROP</span> <span class="hljs-keyword">VIEW</span> <span class="hljs-keyword">IF</span> <span class="hljs-keyword">EXISTS</span> WeigthedRatings;</span> <span class="hljs-operator"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> WeightedRatings <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> name, <span class="hljs-aggregate">SUM</span>(rating*num_ratings)/<span class="hljs-aggregate">SUM</span>(num_ratings) <span class="hljs-keyword">AS</span> WeightedRating <span class="hljs-keyword">FROM</span> movies m, play_in p <span class="hljs-keyword">WHERE</span> m.mid = p.mid <span class="hljs-keyword">GROUP</span> <span class="hljs-keyword">BY</span>(name);</span> <span class="hljs-operator"><span class="hljs-keyword">SELECT</span> name <span class="hljs-keyword">FROM</span> WeightedRatings <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span> WeightedRating <span class="hljs-keyword">DESC</span>, name <span class="hljs-keyword">ASC</span> LIMIT <span class="hljs-number">5</span>;</span> ## (a) Result just like this: name <span class="hljs-comment">-----------------------</span> Adam Kalesperis Aidan Feore Aleksandr Kajdanovsky Alexander Kaidanovsky Alisa Frejndlikh (5 rows) (b) <span class="hljs-operator"><span class="hljs-keyword">DROP</span> <span class="hljs-keyword">VIEW</span> <span class="hljs-keyword">IF</span> <span class="hljs-keyword">EXISTS</span> ActorSumRatings;</span> <span class="hljs-operator"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> ActorSumRatings <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> name, <span class="hljs-aggregate">SUM</span>(num_ratings) <span class="hljs-keyword">as</span> popularity <span class="hljs-keyword">FROM</span> play_in p, movies m <span class="hljs-keyword">WHERE</span> p.mid = m.mid <span class="hljs-keyword">GROUP</span> <span class="hljs-keyword">BY</span> name;</span> <span class="hljs-operator"><span class="hljs-keyword">SELECT</span> name <span class="hljs-keyword">from</span> ActorSumRatings <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span> popularity <span class="hljs-keyword">DESC</span>, name <span class="hljs-keyword">ASC</span> LIMIT <span class="hljs-number">5</span>;</span> ## (b) Result just like this: name <span class="hljs-comment">----------------------</span> Johnny Depp Alan Rickman Orlando Bloom Helena Bonham Carter Matt Damon (5 rows)</code>
The flowing images show the test solution 3 infos in my ubuntu os:
Solution 4
<code class=" hljs sql"><span class="hljs-operator"><span class="hljs-keyword">DROP</span> <span class="hljs-keyword">VIEW</span> <span class="hljs-keyword">IF</span> <span class="hljs-keyword">EXISTS</span> RatingGap;</span> <span class="hljs-operator"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> RatingGap <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> p1.name, <span class="hljs-aggregate">MAX</span>(ABS(m1.rating-m2.rating)) <span class="hljs-keyword">as</span> Gap <span class="hljs-keyword">FROM</span> play_in p1, play_in p2, movies m1, movies m2 <span class="hljs-keyword">WHERE</span> p1.mid = m1.mid <span class="hljs-keyword">and</span> p2.mid = m2.mid <span class="hljs-keyword">and</span> p1.name = p2.name <span class="hljs-keyword">GROUP</span> <span class="hljs-keyword">BY</span>(p1.name);</span> <span class="hljs-operator"><span class="hljs-keyword">SELECT</span> name <span class="hljs-keyword">FROM</span> RatingGap <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span>(Gap) <span class="hljs-keyword">DESC</span> LIMIT <span class="hljs-number">1</span>;</span> ## Result just like this: name <span class="hljs-comment">---------------</span> John Travolta (1 row)</code>
The flowing image show the test solution 4 infos in my ubuntu os:
Solution 5
<code class=" hljs sql"><span class="hljs-operator"><span class="hljs-keyword">DROP</span> <span class="hljs-keyword">VIEW</span> <span class="hljs-keyword">IF</span> <span class="hljs-keyword">EXISTS</span> MastersMovies <span class="hljs-keyword">CASCADE</span>;</span> <span class="hljs-operator"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> MastersMovies <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> m.mid,m.title <span class="hljs-keyword">FROM</span> movies m, play_in p <span class="hljs-keyword">WHERE</span> m.mid = p.mid <span class="hljs-keyword">and</span> p.name = ’Annette Nicole’;</span> <span class="hljs-operator"><span class="hljs-keyword">DROP</span> <span class="hljs-keyword">VIEW</span> <span class="hljs-keyword">IF</span> <span class="hljs-keyword">EXISTS</span> CoActors;</span> <span class="hljs-operator"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> CoActors <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-keyword">DISTINCT</span> name <span class="hljs-keyword">FROM</span> MastersMovies m , play_in p <span class="hljs-keyword">WHERE</span> p.mid = m.mid;</span> <span class="hljs-operator"><span class="hljs-keyword">DROP</span> <span class="hljs-keyword">VIEW</span> <span class="hljs-keyword">IF</span> <span class="hljs-keyword">EXISTS</span> Combinations;</span> <span class="hljs-operator"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> Combinations <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> name,mid <span class="hljs-keyword">FROM</span> MastersMovies , CoActors;</span> <span class="hljs-operator"><span class="hljs-keyword">DROP</span> <span class="hljs-keyword">VIEW</span> <span class="hljs-keyword">IF</span> <span class="hljs-keyword">EXISTS</span> NonExistent;</span> <span class="hljs-operator"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> NonExistent <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> * <span class="hljs-keyword">FROM</span> Combinations <span class="hljs-keyword">EXCEPT</span> (<span class="hljs-keyword">SELECT</span> name, mid <span class="hljs-keyword">FROM</span> play_in);</span> <span class="hljs-operator"><span class="hljs-keyword">DROP</span> <span class="hljs-keyword">VIEW</span> <span class="hljs-keyword">IF</span> <span class="hljs-keyword">EXISTS</span> PotentialResults;</span> <span class="hljs-operator"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> PotentialResults <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> * <span class="hljs-keyword">from</span> CoActors <span class="hljs-keyword">EXCEPT</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-keyword">distinct</span>(name) <span class="hljs-keyword">FROM</span> NonExistent);</span> <span class="hljs-operator"><span class="hljs-keyword">DROP</span> <span class="hljs-keyword">VIEW</span> <span class="hljs-keyword">IF</span> <span class="hljs-keyword">EXISTS</span> NotMastersMovies;</span> <span class="hljs-operator"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> NotMastersMovies <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> m.mid <span class="hljs-keyword">FROM</span> movies m <span class="hljs-keyword">EXCEPT</span> (<span class="hljs-keyword">SELECT</span> mid <span class="hljs-keyword">FROM</span> MastersMovies);</span> <span class="hljs-operator"><span class="hljs-keyword">SELECT</span> * <span class="hljs-keyword">from</span> PotentialResults <span class="hljs-keyword">WHERE</span> name <span class="hljs-keyword">not</span> <span class="hljs-keyword">in</span> (<span class="hljs-keyword">SELECT</span> name <span class="hljs-keyword">FROM</span> play_in p, NotMastersMovies m <span class="hljs-keyword">WHERE</span> m.mid = p.mid <span class="hljs-keyword">UNION</span> <span class="hljs-keyword">SELECT</span> ’Annette Nicole’ ) <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span> name;</span> ## Result just like this: name <span class="hljs-comment">-----------------</span> Christian Perry (1 row) </code>
The flowing image show the test solution 5 infos in my ubuntu os:
Solution 6
<code class=" hljs sql"><span class="hljs-operator"><span class="hljs-keyword">DROP</span> <span class="hljs-keyword">VIEW</span> <span class="hljs-keyword">IF</span> <span class="hljs-keyword">EXISTS</span> MoviesPerYear;</span> <span class="hljs-operator"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> MoviesPerYear <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-keyword">year</span>, <span class="hljs-aggregate">COUNT</span>(title) num_movies <span class="hljs-keyword">FROM</span> MOVIES <span class="hljs-keyword">GROUP</span> <span class="hljs-keyword">BY</span>(<span class="hljs-keyword">year</span>);</span> <span class="hljs-operator"><span class="hljs-keyword">SELECT</span> <span class="hljs-keyword">year</span> <span class="hljs-keyword">from</span> MoviesPerYear <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span> num_movies <span class="hljs-keyword">DESC</span> LIMIT <span class="hljs-number">2</span>;</span> ## Result just like this: year <span class="hljs-comment">------</span> 2006 2007 (2 rows)</code>
The flowing image show the test solution 6 infos in my ubuntu os:
Solution 7
<code class=" hljs vbnet">(a) <span class="hljs-keyword">SELECT</span> COUNT(*) <span class="hljs-keyword">FROM</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-keyword">DISTINCT</span> m1.<span class="hljs-keyword">mid</span>, m2.<span class="hljs-keyword">mid</span> <span class="hljs-keyword">FROM</span> movies m1, movies m2, play_in p1, play_in p2 <span class="hljs-keyword">WHERE</span> m1.<span class="hljs-keyword">mid</span> > m2.<span class="hljs-keyword">mid</span> <span class="hljs-keyword">and</span> m1.<span class="hljs-keyword">mid</span> = p1.<span class="hljs-keyword">mid</span> <span class="hljs-keyword">and</span> m2.<span class="hljs-keyword">mid</span> = p2.<span class="hljs-keyword">mid</span> <span class="hljs-keyword">and</span> p1.name = p2.name) <span class="hljs-keyword">AS</span> count; <span class="hljs-preprocessor">## (a) Result just like this:</span> count -------- <span class="hljs-number">104846</span> (<span class="hljs-number">1</span> row) (b) <span class="hljs-keyword">SELECT</span> COUNT(*) <span class="hljs-keyword">FROM</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-keyword">DISTINCT</span> m1.<span class="hljs-keyword">mid</span>, m2.<span class="hljs-keyword">mid</span> <span class="hljs-keyword">FROM</span> movies m1, movies m2, play_in p1, play_in p2, play_in p3, play_in p4 <span class="hljs-keyword">WHERE</span> m1.<span class="hljs-keyword">mid</span> > m2.<span class="hljs-keyword">mid</span> <span class="hljs-keyword">and</span> m1.<span class="hljs-keyword">mid</span> = p1.<span class="hljs-keyword">mid</span> <span class="hljs-keyword">and</span> m2.<span class="hljs-keyword">mid</span> = p2.<span class="hljs-keyword">mid</span> <span class="hljs-keyword">and</span> m1.<span class="hljs-keyword">mid</span> = p3.<span class="hljs-keyword">mid</span> <span class="hljs-keyword">and</span> m2.<span class="hljs-keyword">mid</span> = p4.<span class="hljs-keyword">mid</span> <span class="hljs-keyword">and</span> p2.name <> p4.name <span class="hljs-keyword">and</span> p1.name = p2.name <span class="hljs-keyword">and</span> p3.name = p4.name) <span class="hljs-keyword">AS</span> count; <span class="hljs-preprocessor">## (b) Result just like this:</span> count ------- <span class="hljs-number">6845</span> (<span class="hljs-number">1</span> row)</code>
The flowing image show the test solution 7 infos in my ubuntu os:
Solution 8
<code class=" hljs sql"><span class="hljs-operator"><span class="hljs-keyword">DROP</span> <span class="hljs-keyword">VIEW</span> <span class="hljs-keyword">IF</span> <span class="hljs-keyword">EXISTS</span> Dominated;</span> <span class="hljs-operator"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> Dominated <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-keyword">DISTINCT</span> m2.mid, m2.title,m2.num_ratings, m2.rating <span class="hljs-keyword">FROM</span> movies m1, movies m2 <span class="hljs-keyword">WHERE</span> m2.rating<=m1.rating <span class="hljs-keyword">and</span> m2.num_ratings<=m1.num_ratings <span class="hljs-keyword">and</span> <span class="hljs-keyword">NOT</span> (m2.rating = m1.rating <span class="hljs-keyword">and</span> m2.num_ratings=m1.num_ratings);</span> <span class="hljs-operator"><span class="hljs-keyword">SELECT</span> title,num_ratings,rating <span class="hljs-keyword">FROM</span> movies <span class="hljs-keyword">EXCEPT</span> (<span class="hljs-keyword">SELECT</span> title,num_ratings,rating <span class="hljs-keyword">FROM</span> Dominated);</span> </code>
The flowing image show the test solution 8 infos in my ubuntu os:
Reference
[1] http://www.ruanyifeng.com/blog/2013/12/getting_started_with_postgresql.html
[2] http://www.postgresql.org/docs/
[3] http://www.cs.cmu.edu/~epapalex/15415S14/PostgreSQLReadme.htm
[4] http://www.cs.cmu.edu/~christos/courses/

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microsoft sql server是Microsoft公司推出的关系型数据库管理系统,是一个全面的数据库平台,使用集成的商业智能(BI)工具提供了企业级的数据管理,具有使用方便可伸缩性好与相关软件集成程度高等优点。SQL Server数据库引擎为关系型数据和结构化数据提供了更安全可靠的存储功能,使用户可以构建和管理用于业务的高可用和高性能的数据应用程序。

结构层次是“数据库→数据表→记录→字段”;字段构成记录,记录构成数据表,数据表构成了数据库。数据库是一个完整的数据的记录的整体,一个数据库包含0到N个表,一个表包含0到N个字段,记录是表中的行。

数据库的“完整性”是指数据的正确性和相容性。完整性是指数据库中数据在逻辑上的一致性、正确性、有效性和相容性。完整性对于数据库系统的重要性:1、数据库完整性约束能够防止合法用户使用数据库时向数据库中添加不合语义的数据;2、合理的数据库完整性设计,能够同时兼顾数据库的完整性和系统的效能;3、完善的数据库完整性有助于尽早发现应用软件的错误。

mysql查询为什么会慢,关于这个问题,在实际开发经常会遇到,而面试中,也是个高频题。遇到这种问题,我们一般也会想到是因为索引。那除开索引之外,还有哪些因素会导致数据库查询变慢呢?


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