Mysql SQLZOO練習(xí)

• • • 0、Select Basics 查詢基礎(chǔ)
    • 1、SELECT names
    • 2、SELECT from WORLD Tutorial
    • 3、SELECT from Nobel Tutorial
    • 4、SELECT within SELECT Tutorial
    • 5、SUM and COUNT
    • 6、The JOIN operation
    • 7、More JOIN operations
    • 8、Using Null
    • 9、Self join

0、Select Basics 查詢基礎(chǔ)

1.The example uses a WHERE clause to show the population of ‘France’. Note that strings (pieces of text that are data) should be in ‘single quotes’;

Modify it to show the population of Germany

Select population FROM world WHERE NAME ="Germany";

2.
Checking a list The word IN allows us to check if an item is in a list. The example shows the name and population for the countries ‘Brazil’, ‘Russia’, ‘India’ and ‘China’.

Show the name and the population for ‘Sweden’, ‘Norway’ and ‘Denmark’.

Select name,population From world Where name in ("Sweden","NorWay","Denmark");

3.
Which countries are not too small and not too big? BETWEEN allows range checking (range specified is inclusive of boundary values). The example below shows countries with an area of 250,000-300,000 sq. km. Modify it to show the country and the area for countries with an area between 200,000 and 250,000.

Select name,area From world Where area Between 200000 and 250000

1、SELECT names

You can use WHERE name LIKE ‘B%’ to find the countries that start with “B”.

The % is a wild-card it can match any characters
Find the country that start with Y

Select name From world Where name LIKE 'Y%'

Find the countries that end with y

Select name From world Where name LIKE "%y"

Luxembourg has an x - so does one other country. List them both.

Find the countries that contain the letter x

SELECT name FROM worldWHERE name LIKE '%x%'

4.
Iceland, Switzerland end with land - but are there others?

Find the countries that end with land

SELECT name FROM worldWHERE name LIKE '%land'

5.
Columbia starts with a C and ends with ia - there are two more like this.

Find the countries that start with C and end with ia

SELECT name FROM worldWHERE name LIKE 'C%ia'

Greece has a double e - who has a double o?

Find the country that has oo in the name

SELECT name FROM world WHERE name LIKE "%oo%"

7.
Bahamas has three a - who else?

Find the countries that have three or more a in the name

SELECT name FROM worldWHERE name LIKE '%a%a%a%'

8.
India and Angola have an n as the second character. You can use the underscore as a single character wildcard.

SELECT name FROM worldWHERE name LIKE '_n%' ORDER BY name

Find the countries that have “t” as the second character.

SELECT name FROM worldWHERE name LIKE '_t%' ORDER BY name

9.
Lesotho and Moldova both have two o characters separated by two other characters.

Find the countries that have two “o” characters separated by two others.

SELECT name FROM worldWHERE name LIKE '%o__o%'

10.
Cuba and Togo have four characters names.

Find the countries that have exactly four characters.

SELECT name FROM worldWHERE name LIKE '____'

The capital of Luxembourg is Luxembourg. Show all the countries where the capital is the same as the name of the country

Find the country where the name is the capital city.

SELECT nameFROM worldWHERE name = capital

The capital of Mexico is Mexico City. Show all the countries where the capital has the country together with the word “City”.
Find the country where the capital is the country plus “City”.

SELECT name FROM world WHERE capital LIKE '_%City' SELECT name FROM world WHERE capital LIKE concat(name,' City')

13.
Find the capital and the name where the capital includes the name of the country.

Select capital,name FROM world WHERE capital LIKE concat(name,'%')

14.
Find the capital and the name where the capital is an extension of name of the country.

You should include Mexico City as it is longer than Mexico. You should not include Luxembourg as the capital is the same as the country.

SELECT capital,name FROM world WHERE capital LIKE concat(name,'%') AND capital != name;

15.
For Monaco-Ville the name is Monaco and the extension is -Ville.

Show the name and the extension where the capital is an extension of name of the country.

You can use the SQL function REPLACE.

In this example you remove all the 'a’s from the name of each country. This happens because the string ‘a(chǎn)’ is replaced with .

SELECT name,REPLACE(name, 'a','')FROM bbc

2、SELECT from WORLD Tutorial

Read the notes about this table. Observe the result of running this SQL command to show the name, continent and population of all countries.

SELECT name, continent, population FROM world

How to use WHERE to filter records. Show the name for the countries that have a population of at least 200 million. 200 million is 200000000, there are eight zeros.

SELECT name FROM world WHERE population >= 200000000

3.
Give the name and the per capita GDP for those countries with a population of at least 200 million.

HELP:How to calculate per capita GDP
per capita GDP is the GDP divided by the population GDP/population

SELECT name,(GDP/population) FROM world WHERE population >= 200000000

4.
Show the name and population in millions for the countries of the continent ‘South America’. Divide the population by 1000000 to get population in millions.

SELECT name,(population/1000000) FROM world WHERE continent LIKE 'South America'

5.
Show the name and population for France, Germany, Italy

SELECT name,population FROM world WHERE name in('France','Germany','Italy')

6.
Show the countries which have a name that includes the word ‘United’

SELECT name FROM world WHERE name LIKE '%United%'

7.
Two ways to be big: A country is big if it has an area of more than 3 million sq km or it has a population of more than 250 million.

Show the countries that are big by area or big by population. Show name, population and area.

SELECT name,population,area FROM world WHERE area>3000000 OR population >250000000

8.
Exclusive OR (XOR). Show the countries that are big by area (more than 3 million) or big by population (more than 250 million) but not both. Show name, population and area.

Australia has a big area but a small population, it should be included.
Indonesia has a big population but a small area, it should be included.
China has a big population and big area, it should be excluded.
United Kingdom has a small population and a small area, it should be excluded.

SELECT name,population,area FROM world WHERE area>3000000 XOR population >250000000

9.
Show the name and population in millions and the GDP in billions for the countries of the continent ‘South America’. Use the ROUND function to show the values to two decimal places.

For South America show population in millions and GDP in billions both to 2 decimal places.
Millions and billions

SELECT name,ROUND(population/1000000,2),ROUND(GDP/1000000000,2) FROM world WHERE continent ='South America'

10.
Show the name and per-capita GDP for those countries with a GDP of at least one trillion (1000000000000; that is 12 zeros). Round this value to the nearest 1000.

Show per-capita GDP for the trillion dollar countries to the nearest $1000.

SELECT name,ROUND(GDP/population,-3) FROM world WHERE GDP >=1000000000000

11.
Greece has capital Athens.

Each of the strings ‘Greece’, and ‘Athens’ has 6 characters.

Show the name and capital where the name and the capital have the same number of characters.

You can use the LENGTH function to find the number of characters in a string

SELECT name,capital FROM world WHERE LENGTH(capital) = LENGTH(name)

12.
The capital of Sweden is Stockholm. Both words start with the letter ‘S’.

Show the name and the capital where the first letters of each match. Don’t include countries where the name and the capital are the same word.
You can use the function LEFT to isolate the first character.
You can use <> as the NOT EQUALS operator.

SELECT name,capital FROM world WHERE name <> capital AND LEFT(name,1) = LEFT(capital,1)

13.
Equatorial Guinea and Dominican Republic have all of the vowels (a e i o u) in the name. They don’t count because they have more than one word in the name.

Find the country that has all the vowels and no spaces in its name.

You can use the phrase name NOT LIKE ‘%a%’ to exclude characters from your results.
The query shown misses countries like Bahamas and Belarus because they contain at least one ‘a(chǎn)’

select name from world where name LIKE '%a%' AND name LIKE '%i%'AND name LIKE '%e%'AND name LIKE '%o%'AND name LIKE '%u%'AND name NOT LIKE '% %'

3、SELECT from Nobel Tutorial

Change the query shown so that it displays Nobel prizes for 1950.

SELECT yr, subject, winnerFROM nobelWHERE yr = 1950

2.
Show who won the 1962 prize for literature.

SELECT winnerFROM nobelWHERE yr = 1962AND subject = 'literature'

3.
Show the year and subject that won ‘Albert Einstein’ his prize.

select yr,subject from nobel where winner = 'Albert Einstein'

Give the name of the ‘peace’ winners since the year 2000, including 2000.

select winner from nobel where subject = 'peace' AND yr >= 2000

5.
Show all details (yr, subject, winner) of the literature prize winners for 1980 to 1989 inclusive.

select * from nobel where subject = 'literature' AND yr>=1980 AND yr <=1989

6.
Show all details of the presidential winners:

Theodore Roosevelt
Thomas Woodrow Wilson
Jimmy Carter
Barack Obama

SELECT * FROM nobelWHERE winner IN ('Theodore Roosevelt','Woodrow Wilson','Jimmy Carter','Barack Obama')

7.
Show the winners with first name John

select winner from nobel where winner LIKE 'John_%'

8.
Show the year, subject, and name of physics winners for 1980 together with the chemistry winners for 1984.

select yr,subject,winner from nobel where (yr=1980 AND subject ='physics') OR (yr=1984 AND subject='chemistry')

9.
Show the year, subject, and name of winners for 1980 excluding chemistry and medicine

select yr,subject,winner from nobel where yr=1980 AND subject NOT IN('chemistry','medicine')

10.
Show year, subject, and name of people who won a ‘Medicine’ prize in an early year (before 1910, not including 1910) together with winners of a ‘Literature’ prize in a later year (after 2004, including 2004)

SELECT yr, subject, winner FROM nobel WHERE (subject = 'Medicine' AND yr < 1910 )OR(subject ='Literature' and yr >= 2004);

11.
Find all details of the prize won by PETER GRüNBERG

Non-ASCII characters

select * from nobel where winner = 'PETER GRüNBERG'

12.
Find all details of the prize won by EUGENE O’NEILL

Escaping single quotes
You can’t put a single quote in a quote string directly. You can use two single quotes within a quoted string.

select * from nobel where winner = 'EUGENE O\'NEILL'

13.
Knights in order

List the winners, year and subject where the winner starts with Sir. Show the the most recent first, then by name order.

select winner,yr,subject from nobel where winner LIKE 'Sir%' //ODER BY yr DESC,winner

The expression subject IN (‘chemistry’,‘physics’) can be used as a value - it will be 0 or 1.

Show the 1984 winners and subject ordered by subject and winner name; but list chemistry and physics last.

SELECT winner, subjectFROM nobelWHERE yr=1984ORDER BY subject IN ('physics','chemistry'),subject,winner

4、SELECT within SELECT Tutorial

List each country name where the population is larger than that of ‘Russia’.

world(name, continent, area, population, gdp) SELECT name FROM worldWHERE population >(SELECT population FROM worldWHERE name='Russia')

2.
Show the countries in Europe with a per capita GDP greater than ‘United Kingdom’.

Per Capita GDP
The per capita GDP is the gdp/population

select name from world where continent = 'Europe' AND GDP/population > (select gdp/population from world where name = 'United Kingdom')

3.

List the name and continent of countries in the continents containing either Argentina or Australia. Order by name of the country.

select name,continent from world where continent IN (select continent from world where name IN ('Argentina','Australia')) order by name

4.
Which country has a population that is more than United Kingom but less than Germany? Show the name and the population.

select name,population from world where population > (select population from world where name = 'United Kingdom' ) AND population < (select population from world where name = 'Germany' )

5.
Germany (population 80 million) has the largest population of the countries in Europe. Austria (population 8.5 million) has 11% of the population of Germany.

Show the name and the population of each country in Europe. Show the population as a percentage of the population of Germany.

The format should be Name, Percentage for example:

name percentage
Albania 3%
Andorra 0%
Austria 11%
… …
Decimal places
Percent symbol %
You can use the function CONCAT to add the percentage symbol.

select name,CONCAT(ROUND(100*population/(select population from world where name = 'Germany'),0),'%') AS percentage from world where continent = 'Europe'

6.
Which countries have a GDP greater than every country in Europe? [Give the name only.] (Some countries may have NULL gdp values)

select name from world where GDP>(select MAX(GDP) from world where continent = 'Europe' AND GDP > 0)

7.
Find the largest country (by area) in each continent, show the continent, the name and the area:

select continent,name,area from world x where area >= ALL(select area from world ywhere y.continent = x.continent AND area>0)

8.
List each continent and the name of the country that comes first alphabetically.

select w1.continent,w1.name from world w1 where w1.name <=all( select w2.name from world w2 where w1.continent = w2.continent)

9.
Find the continents where all countries have a population <= 25000000. Then find the names of the countries associated with these continents. Show name, continent and population.

select w1.name,w1.continent,w1.population from world w1 where 25000000 >= (select MAX(w2.population) from world w2 where w1.continent = w2.continent group by w2.continent)

10.
Some countries have populations more than three times that of all of their neighbours (in the same continent). Give the countries and continents.

select w1.name,w1.continent from world w1 where w1.population/3 >= ALL(select w2.population from world w2 where w1.continent =w2.continent AND w1.name != w2.name)

5、SUM and COUNT

Show the total population of the world.

world(name, continent, area, population, gdp) SELECT SUM(population) FROM world

2.
List all the continents - just once each.

SELECT distinct(continent) FROM world

3.
Give the total GDP of Africa

select sum(gdp) from world where continent = 'Africa'

4.
How many countries have an area of at least 1000000

select count(name) AS COUNT from world where area >=1000000

5.
What is the total population of (‘Estonia’, ‘Latvia’, ‘Lithuania’)

select sum(population) AS ALLPOPULATION from world where name in ('Estonia','Latvia','Lithuania')

6.
For each continent show the continent and number of countries.

select continent,count(name) from world group by continent

7.
For each continent show the continent and number of countries with populations of at least 10 million.

SELECT continent, COUNT(name) FROM world WHERE population >= 10000000 GROUP BY continent;

8.
List the continents that have a total population of at least 100 million.

select continent from world group by continent having sum(population) >= 100000000

6、The JOIN operation

The first example shows the goal scored by a player with the last name ‘Bender’. The * says to list all the columns in the table - a shorter way of saying matchid, teamid, player, gtime

Modify it to show the matchid and player name for all goals scored by Germany. To identify German players, check for: teamid = ‘GER’

SELECT matchid,player FROM goal WHERE teamid = 'GER'

2.
From the previous query you can see that Lars Bender’s scored a goal in game 1012. Now we want to know what teams were playing in that match.

Notice in the that the column matchid in the goal table corresponds to the id column in the game table. We can look up information about game 1012 by finding that row in the game table.

Show id, stadium, team1, team2 for just game 1012

select id,stadium,team1,team2 from game where id = '1012'

3.
You can combine the two steps into a single query with a JOIN.

SELECT *FROM game JOIN goal ON (id=matchid)

The FROM clause says to merge data from the goal table with that from the game table. The ON says how to figure out which rows in game go with which rows in goal - the matchid from goal must match id from game. (If we wanted to be more clear/specific we could say
ON (game.id=goal.matchid)

The code below shows the player (from the goal) and stadium name (from the game table) for every goal scored.

Modify it to show the player, teamid, stadium and mdate for every German goal.

SELECT player,teamid,stadium,mdateFROM game JOIN goal ON (id=matchid) AND teamid = 'GER'

4.
Use the same JOIN as in the previous question.

Show the team1, team2 and player for every goal scored by a player called Mario
player LIKE 'Mario%

select team1,team2,player from game JOIN goal ON (id=matchid) where player LIKE 'Mario%'

5.
The table eteam gives details of every national team including the coach. You can JOIN goal to eteam using the phrase goal JOIN eteam on teamid=id

Show player, teamid, coach, gtime for all goals scored in the first 10 minutes gtime<=10

SELECT player, teamid, coach,gtimeFROM goal JOIN eteam ON (teamid=id)WHERE gtime<=10

6.
To JOIN game with eteam you could use either
game JOIN eteam ON (team1=eteam.id) or game JOIN eteam ON (team2=eteam.id)

Notice that because id is a column name in both game and eteam you must specify eteam.id instead of just id

List the dates of the matches and the name of the team in which ‘Fernando Santos’ was the team1 coach.

select mdate,teamname from game JOIN eteam ON (team1=eteam.id) where coach='Fernando Santos'

7.
List the player for every goal scored in a game where the stadium was ‘National Stadium, Warsaw’

select player from goal JOIN game ON (matchid=id) where stadium ='National Stadium, Warsaw'

8.
The example query shows all goals scored in the Germany-Greece quarterfinal.
Instead show the name of all players who scored a goal against Germany.

HINT
Select goals scored only by non-German players in matches where GER was the id of either team1 or team2. You can use teamid!='GER' to prevent listing German players. You can use DISTINCT to stop players being listed twice.

SELECT DISTINCT(player)FROM game JOIN goal ON (matchid = id )WHERE teamid!='GER' AND (team1='GER'OR team2='GER')

9.
Show teamname and the total number of goals scored.
COUNT and GROUP BY
You should COUNT(*) in the SELECT line and GROUP BY teamname

select teamname,COUNT(matchid) from eteam JOIN goal ON (id = teamid) GROUP BY teamname

10.
Show the stadium and the number of goals scored in each stadium.

select stadium,COUNT(matchid) from game JOIN goal ON (matchid=id) GROUP BY stadium

11.
For every match involving ‘POL’, show the matchid, date and the number of goals scored.

SELECT matchid,mdate,COUNT(matchid)FROM game JOIN goal ON matchid = id WHERE (team1 = 'POL' OR team2 = 'POL') GROUP BY matchid,mdate

12.
For every match where ‘GER’ scored, show matchid, match date and the number of goals scored by ‘GER’

select matchid,mdate,COUNT(matchid) from game JOIN goal ON (id=matchid) where teamid='GER' GROUP BY matchid,mdate

13.
List every match with the goals scored by each team as shown. This will use “CASE WHEN” which has not been explained in any previous exercises.
mdate team1 score1 team2 score2
1 July 2012 ESP 4 ITA 0
10 June 2012 ESP 1 ITA 1
10 June 2012 IRL 1 CRO 3
…
Notice in the query given every goal is listed. If it was a team1 goal then a 1 appears in score1, otherwise there is a 0. You could SUM this column to get a count of the goals scored by team1. Sort your result by mdate, matchid, team1 and team2.

SELECT mdate, team1, SUM(CASE WHEN team1 = teamid THEN 1 ELSE 0 END) AS score1, team2, SUM(CASE WHEN team2 = teamid THEN 1 ELSE 0 END) AS score2 FROM game LEFT JOIN goal ON id = matchid GROUP BY mdate, team1,team2; ORDER BY mdate, matchid, team1, team2;

7、More JOIN operations

List the films where the yr is 1962 [Show id, title]

SELECT id, titleFROM movieWHERE yr=1962

2.
Give year of ‘Citizen Kane’.

SELECT yr FROM movie WHERE title ='Citizen Kane'

3.
List all of the Star Trek movies, include the id, title and yr (all of these movies include the words Star Trek in the title). Order results by year.

SELECT id,title,yr FROM movie WHERE title LIKE '%Star Trek%' ORDER BY yr

4.
What id number does the actor ‘Glenn Close’ have?

SELECT id FROM actor WHERE name='Glenn Close'

5.
What is the id of the film ‘Casablanca’

SELECT id FROM movie WHERE title = 'Casablanca'

6.
Obtain the cast list for ‘Casablanca’.

what is a cast list?
The cast list is the names of the actors who were in the movie.

Use movieid=11768, (or whatever value you got from the previous question)

SELECT name FROM actor A JOIN casting B ON (A.id = B.actorid) WHERE movieid = (SELECT id FROM movie WHERE title = 'Casablanca')

7.
Obtain the cast list for the film ‘Alien’

SELECT name FROM actor A JOIN casting B ON (A.id=B.actorid) WHERE movieid = (SELECT id FROM movie WHERE title = 'Alien')

8.
List the films in which ‘Harrison Ford’ has appeared

SELECT title FROM movie A JOIN casting B ON (A.id = B.movieid) WHERE B.actorid = (SELECT id FROM actor WHERE name = 'Harrison Ford')

9.
List the films where ‘Harrison Ford’ has appeared - but not in the starring role. [Note: the ord field of casting gives the position of the actor. If ord=1 then this actor is in the starring role]

SELECT title FROM movie A JOIN casting B ON (A.id = B.movieid) JOIN actor C ON (C.id = B.actorid) WHERE C.name = 'Harrison Ford' AND B.ord<>1

10.
List the films together with the leading star for all 1962 films.

SELECT M.title,A.name FROM casting C JOIN actor A ON (C.actorid = A.id) JOIN movie M ON (M.id = C.movieid) WHERE M.yr = '1962' AND C.ord = '1'

11.
Which were the busiest years for ‘Rock Hudson’, show the year and the number of movies he made each year for any year in which he made more than 2 movies.

SELECT yr,COUNT(M.id) FROM movie M JOIN casting C ON (M.id=C.movieid) JOIN actor A ON (A.id = C.actorid) WHERE A.name = 'Rock Hudson' GROUP BY yr HAVING COUNT(M.id) >2;

12.
List the film title and the leading actor for all of the films ‘Julie Andrews’ played in.

Did you get “Little Miss Marker twice”?
Julie Andrews starred in the 1980 remake of Little Miss Marker and not the original(1934).

Title is not a unique field, create a table of IDs in your subquery

SELECT title,A.name FROM movie M JOIN casting C ON (M.id = C.movieid) JOIN actor A ON (A.id = C.actorid) WHERE C.ord =1 AND M.id IN(SELECT CC.movieid FROM casting CC JOIN actor AA ON (AA.id = CC.actorid) WHERE AA.name ='Julie Andrews')

13.
Obtain a list, in alphabetical order, of actors who’ve had at least 15 starring roles.

SELECT A.name FROM actor A JOIN casting C ON (A.id = C.actorid) WHERE C.ord =1 GROUP BY A.name HAVING COUNT(C.movieid)>=15

14.
List the films released in the year 1978 ordered by the number of actors in the cast, then by title.

SELECT M.title,COUNT(C.actorid) FROM movie M JOIN casting C ON ( M.id = C.movieid) JOIN actor A ON (A.id = C.actorid) WHERE M.yr = 1978 GROUP BY C.movieid ORDER BY COUNT(A.id) DESC,M.title

15.
List all the people who have worked with ‘Art Garfunkel’.

SELECT name FROM actor A JOIN casting C ON (A.id = C.actorid) WHERE name <>'Art Garfunkel' AND C.movieid IN ( SELECT movieid FROM casting WHERE actorid = (SELECT id FROM actor WHERE name = 'Art Garfunkel') )

8、Using Null

List the teachers who have NULL for their department.

Why we cannot use =
You might think that the phrase dept=NULL would work here but it doesn’t - you can use the phrase dept IS NULL

That’s not a proper explanation.
No it’s not, but you can read a better explanation at Wikipedia:NULL.

SELECT name FROM teacher WHERE dept IS NULL;

Note the INNER JOIN misses the teachers with no department and the departments with no teacher.

SELECT teacher.name, dept.nameFROM teacher INNER JOIN deptON (teacher.dept=dept.id)

Use a different JOIN so that all teachers are listed.

SELECT Tec.name ,Dep.name FROM teacher Tec LEFT JOIN dept Dep ON (Tec.dept = Dep.id)

4.
Use a different JOIN so that all departments are listed.

SELECT Tec.name ,Dep.name FROM teacher Tec RIGHT JOIN dept Dep ON (Tec.dept = Dep.id)

5.
Use COALESCE to print the mobile number. Use the number ‘07986 444 2266’ if there is no number given. Show teacher name and mobile number or ‘07986 444 2266’

SELECT name,COALESCE(mobile,'07986 444 2266') AS mob FROM teacher

6.
Use the COALESCE function and a LEFT JOIN to print the teacher name and department name. Use the string ‘None’ where there is no department.

SELECT T.name, COALESCE(D.name,'None') AS departmentname FROM teacher T LEFT JOIN dept D ON (D.id =T.dept )

7.
Use COUNT to show the number of teachers and the number of mobile phones.

SELECT COUNT(id),COUNT(mobile) FROM teacher

8.
Use COUNT and GROUP BY dept.name to show each department and the number of staff. Use a RIGHT JOIN to ensure that the Engineering department is listed.

SELECT D.name,COUNT(T.id) FROM teacher T RIGHT JOIN dept D ON (D.id = T.dept) GROUP BY D.id,D.name

9.
Use CASE to show the name of each teacher followed by ‘Sci’ if the teacher is in dept 1 or 2 and ‘Art’ otherwise.

SELECT name, CASE WHEN dept IN (1,2) THEN 'Sci'WHEN dept IS NULL THEN 'Art'ELSE 'Art'END FROM teacher;

10.
Use CASE to show the name of each teacher followed by ‘Sci’ if the teacher is in dept 1 or 2, show ‘Art’ if the teacher’s dept is 3 and ‘None’ otherwise.

SELECT name, CASE WHEN dept IN (1,2) THEN 'Sci'WHEN dept IS NULL THEN 'None'ELSE 'Art'END FROM teacher;

9、Self join

How many stops are in the database.

SELECT COUNT(id) FROM stops;

2.
Find the id value for the stop ‘Craiglockhart’

SELECT id FROM stops WHERE name = 'Craiglockhart'

3.
Give the id and the name for the stops on the ‘4’ ‘LRT’ service.

SELECT S.id,S.name FROM route R JOIN stops S ON (S.id = R.stop) WHERE R.num = '4' AND R.company = 'LRT'; SELECT id, name FROM stops s JOIN route r ON s.id = r.stop WHERE num = '4' AND company = 'LRT';

4.
The query shown gives the number of routes that visit either London Road (149) or Craiglockhart (53). Run the query and notice the two services that link these stops have a count of 2. Add a HAVING clause to restrict the output to these two routes.

SELECT company, num, COUNT(*) FROM route WHERE stop=149 OR stop=53 GROUP BY company, num HAVING COUNT(*) = 2;

5.
Execute the self join shown and observe that b.stop gives all the places you can get to from Craiglockhart, without changing routes. Change the query so that it shows the services from Craiglockhart to London Road.

SELECT a.company, a.num, a.stop, b.stop FROM route a JOIN route b ON(a.company=b.company AND a.num=b.num) WHERE a.stop='53' AND b.stop = '149'

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