Add MyXQL support for lateral joins (#339)

Author: João Paulo

lib/ecto/adapters/myxql/connection.ex

@@ -359,11 +359,12 @@ if Code.ensure_loaded?(MyXQL) do
     defp join_on(_qual, expr, sources, query), do: [" ON " | expr(expr, sources, query)]
 
     defp join_qual(:inner, _), do: " INNER JOIN "
+    defp join_qual(:inner_lateral, _), do: " INNER JOIN LATERAL "
     defp join_qual(:left, _),  do: " LEFT OUTER JOIN "
+    defp join_qual(:left_lateral, _),  do: " LEFT OUTER JOIN LATERAL "
     defp join_qual(:right, _), do: " RIGHT OUTER JOIN "
     defp join_qual(:full, _),  do: " FULL OUTER JOIN "
     defp join_qual(:cross, _), do: " CROSS JOIN "
-    defp join_qual(mode, q),   do: error!(q, "join `#{inspect mode}` not supported by MySQL")
 
     defp where(%{wheres: wheres} = query, sources) do
       boolean(" WHERE ", wheres, sources, query)

test/ecto/adapters/myxql_test.exs

@@ -893,6 +893,18 @@ defmodule Ecto.Adapters.MyXQLTest do
            "SELECT s0.`id`, s1.`id` FROM `schema` AS s0 LEFT OUTER JOIN `schema2` AS s1 ON TRUE"
   end
 
+  test "lateral join with fragment" do
+    query = Schema
+            |> join(:inner_lateral, [p], q in fragment("SELECT * FROM schema2 AS s2 WHERE s2.id = ? AND s2.field = ?", p.x, ^10))
+            |> select([p, q], {p.id, q.z})
+            |> where([p], p.id > 0 and p.id < ^100)
+            |> plan()
+    assert all(query) ==
+           ~s{SELECT s0.`id`, f1.`z` FROM `schema` AS s0 INNER JOIN LATERAL } <>
+           ~s{(SELECT * FROM schema2 AS s2 WHERE s2.id = s0.`x` AND s2.field = ?) AS f1 ON TRUE } <>
+           ~s{WHERE ((s0.`id` > 0) AND (s0.`id` < ?))}
+  end
+
   test "cross join" do
     query = from(p in Schema, cross_join: c in Schema2, select: {p.id, c.id}) |> plan()
     assert all(query) ==
@@ -1406,16 +1418,6 @@ defmodule Ecto.Adapters.MyXQLTest do
 
   # Unsupported types and clauses
 
-  test "lateral join with fragment" do
-    assert_raise Ecto.QueryError, ~r"join `:inner_lateral` not supported by MySQL", fn ->
-      Schema
-      |> join(:inner_lateral, [p], q in fragment("SELECT * FROM schema2 AS s2 WHERE s2.id = ? AND s2.field = ?", p.x, ^10))
-      |> select([p, q], {p.id, q.z})
-      |> plan()
-      |> all
-    end
-  end
-
   test "arrays" do
     assert_raise Ecto.QueryError, ~r"Array type is not supported by MySQL", fn ->
       query = Schema |> select([], fragment("?", [1, 2, 3])) |> plan()