Get rows

df.single { age == 45 }
df.first { weight != null }
df.minBy { age }
df.maxBy { name.firstName.length }
df.maxByOrNull { weight }

val age by column<Int>()
val weight by column<Int?>()
val name by columnGroup()
val firstName by name.column<String>()

df.single { age() == 45 }
df.first { weight() != null }
df.minBy(age)
df.maxBy { firstName().length }
df.maxByOrNull { weight() }

df.single { "age"<Int>() == 45 }
df.first { it["weight"] != null }
df.minBy("weight")
df.maxBy { "name"["firstName"]<String>().length }
df.maxByOrNull("weight")