ifExists

foo.scala

val (u, g) = (User.syntax("u"), Group.syntax("g"))
val groupId: Option[GroupId] = ...

// getOrElse
sql"""
SELECT
  ${u.result.*}
  ${groupId.map(v => sqls", ${g.result.name}") getOrElse sqls""}
FROM
  ${User as u}
  ${groupId.map(v => sqls"INNER JOIN ${Group as g} ON ${u.groupCode} = ${g.code} AND  ${g.id} = ${v}") getOrElse sqls""}
"""

// fold
sql"""
SELECT
  ${u.result.*}
  ${groupId.fold(sqls"")(v => sqls", ${g.result.name}")}
FROM
  ${User as u}
  ${groupId.fold(sqls"")(v => sqls"INNER JOIN ${Group as g} ON ${u.groupCode} = ${g.code} AND  ${g.id} = ${v}")}
"""

// skipIfAbsent
sql"""
SELECT
  ${u.result.*}
  ${sqls.skipIfAbsent(groupId.map(v => sqls", ${g.result.name}"))}
FROM
  ${User as u}
  ${sqls.skipIfAbsent(groupId.map(v => sqls"INNER JOIN ${Group as g} ON ${u.groupCode} = ${g.code} AND  ${g.id} = ${v}"))}
"""

// ifExists
sql"""
SELECT
  ${u.result.*}
  ${groupId.map(v => sqls", ${g.result.name}").ifExists}
FROM
  ${User as u}
  ${groupId.map(v => sqls"INNER JOIN ${Group as g} ON ${u.groupCode} = ${g.code} AND  ${g.id} = ${v}").ifExists}
"""