Learn SQL With Rails 4 - Single Table Queries
| Question | Click to View Answer |
Create a rails application called single_table_queries. |
$ rails new single_table_queries
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Create an Article model with a title attribute (string datatype). Create the articles table in the database. |
$ rails g model Article title:string
$ rake db:migrate
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What SQL is generated to create the articles table in the database. |
CREATE TABLE "articles" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "title" varchar(255), "created_at" datetime, "updated_at" datetime);
Only mark this answer as correct if you can write this entire SQL statement flawlessly. |
What SQL does the following code generate? Article.create(title: "blah blah blah")
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INSERT INTO "articles" ("created_at", "title", "updated_at")
VALUES (?, ?, ?) [["created_at", "2014-06-27 18:25:38.638132"], ["title", "blah blah blah"], ["updated_at", "2014-06-27 18:25:38.638132"]]
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Update the seed file, so it creates 100 articles with 8 character random strings as the title. |
# db/seeds.rb
def random_string(n)
('a'..'z').to_a.shuffle[0..n-1].join
end
100.times do
str = random_string(8)
Article.create!(title: str)
end
# command line
$ rake db:seed
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What SQL does the following code generate? Article.find(1)
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SELECT "articles".* FROM "articles" WHERE "articles"."id" = ? LIMIT 1 [["id", 1]]
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What SQL does the following code generate? Article.all
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SELECT "articles".* FROM "articles"
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What SQL does the following code generate? Article.first
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SELECT "articles".* FROM "articles" ORDER BY "articles"."id" ASC LIMIT 1
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What SQL does the following code generate? Article.last(5)
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SELECT "articles".* FROM "articles" ORDER BY "articles"."id" DESC LIMIT 5
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Write an ActiveRecord query to fetch all articles with a title that starts with the letter 'b'. What is the SQL generated by this query. |
# ActiveRecord query
Article.where("title LIKE ?", "b%")
-- SQL query
SELECT "articles".* FROM "articles" WHERE (title LIKE 'b%')
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Write an ActiveRecord query to fetch all articles with a title that's 8 characters long. What is the SQL generated by this query. |
# ActiveRecord query
Article.where("length(title) = 8")
-- SQL query
SELECT "articles".* FROM "articles" WHERE (length(title) = 8)
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