在Ruby中有条件地复合SQL查询

if condition
  # code to be executed if condition is true
elsif condition2
  # code to be executed if condition2 is true
else
  # code to be executed if none of the above conditions are true
end

case variable
when value1
  # code to be executed if variable equals value1
when value2
  # code to be executed if variable equals value2
else
  # code to be executed if none of the above conditions are true
end

result = condition ? value_if_true : value_if_false

# 导入必要的库和模型
require 'active_record'

# 定义数据库连接配置
ActiveRecord::Base.establish_connection(
  adapter: 'mysql2',
  host: 'localhost',
  username: 'root',
  password: 'password',
  database: 'my_database'
)

# 定义模型类
class User < ActiveRecord::Base
end

# 条件地复合SQL查询
users = User.where("age > ?", 18).where("gender = ?", "male")

# 遍历查询结果
users.each do |user|
  puts user.name
end