Railsドキュメント(v6.0.2.1)

モデル.where(条件)

Page.where("category_id = '1'")
# SELECT "pages".* FROM "pages" WHERE "pages"."category_id" = 1

Page.where(category_id: 1)
# SELECT "pages".* FROM "pages" WHERE "pages"."category_id" = 1

Page.where(["category_id = ? and url_id = ?", 1, 1])
# SELECT "pages".* FROM "pages" WHERE (category_id = 1 and url_id = 1)

Page.where("category_id = :category_id", {category_id: params[:category_id]})

Page.where(category_id: [1, 2])
# SELECT * FROM pages WHERE (pages.category_id IN (1,2))

Page.where(title: nil)

Page.not.where category_id: 1
# SELECT * FROM pages WHERE (pages.category_id != 1)

Page.where(category_id: 1).where(user_id: 1)

Page.where(category_id: 1).or(Page.where(user_id: 1))

User.where(:id => 1..10)

User.where("name like '%hoge%'")

User.where(created_at: '2020-1-5'.in_time_zone.all_year)

User.where(created_at: '2020-1-5'.in_time_zone.all_month)

User.where(created_at: '2020-1-5'.in_time_zone.all_day)

User.where(age: 20..)
# SELECT * FROM users WHERE (users.age >= 20)