Add aliases to nested subselects

quill-sql-portable/src/main/scala/io/getquill/sql/idiom/SqlIdiom.scala

@@ -82,7 +82,13 @@ trait SqlIdiom extends Idiom {
 
   def astTokenizer(implicit astTokenizer: Tokenizer[Ast], strategy: NamingStrategy): Tokenizer[Ast] =
     Tokenizer[Ast] {
-      case a: Query           => SqlQuery(a).token
+      case a: Query =>
+        // This case almost exclusively happens when you have a select inside of an insert.
+        // have a look at the SqlDslSpec `forUpdate` and `insert with subselects` tests
+        // for more details.
+        // Right now we are not removing extra select clauses here (via RemoveUnusedSelects) since I am not sure what
+        // kind of impact that could have on selects. Can try to do that in the future.
+        RemoveExtraAlias(strategy)(ExpandNestedQueries(SqlQuery(a))).token
       case a: Operation       => a.token
       case a: Infix           => a.token
       case a: Action          => a.token

quill-sql/src/test/scala/io/getquill/context/sql/InsertSubquerySpec.scala

@@ -0,0 +1,8 @@
+package io.getquill.context.sql
+
+import io.getquill.{ Insert, Spec }
+import io.getquill.context.sql.testContext._
+
+class InsertSubquerySpec extends Spec {
+
+}

quill-sql/src/test/scala/io/getquill/context/sql/dsl/SqlDslSpec.scala

@@ -1,6 +1,6 @@
 package io.getquill.context.sql.dsl
 
-import io.getquill.Spec
+import io.getquill.{ Insert, Query, Quoted, Spec }
 import io.getquill.context.sql.testContext
 import io.getquill.context.sql.testContext._
 
@@ -22,9 +22,29 @@ class SqlDslSpec extends Spec {
   }
 
   "forUpdate" in {
-    val q = quote {
+    val q: Quoted[Query[TestEntity]] = quote {
       query[TestEntity].filter(t => t.s == "a").forUpdate
     }
     testContext.run(q).string mustEqual "SELECT t.s, t.i, t.l, t.o, t.b FROM TestEntity t WHERE t.s = 'a' FOR UPDATE"
   }
+
+  case class Person(name: String, age: Int)
+
+  "insert with subselects" - {
+    // In this case we are not renaming the ages into the table, just the names so technically
+    // we can exclude the age columns. I am not sure if that has some other potential issues
+    // for inserts so for now I am just doing ExpandNestedSelects and RemoveUnusedAliases.
+    // have a look at `astTokenizer` in `SqlIdiom` for details.
+    val q1 = quote {
+      (query[Person].map(p => Person("x", p.age)) union query[Person]).map(_.name)
+    }
+
+    val q2 = quote {
+      infix"INSERT into names $q1".as[Insert[Person]]
+    }
+
+    "should show all field aliases" in {
+      testContext.run(q2).string mustEqual "INSERT into names SELECT x1.name FROM ((SELECT 'x' AS name, p.age FROM Person p) UNION (SELECT x.name, x.age FROM Person x)) AS x1"
+    }
+  }
 }