Fix unsafe branch collapsing of an outer JOIN (#68)

MechanicalRabbit · Jul 3, 2024 · a6a31bd · a6a31bd
1 parent 3abed0b
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diff --git a/docs/src/test/nodes.md b/docs/src/test/nodes.md
@@ -3286,6 +3286,116 @@ Nested subqueries that are combined with `Join` may fail to collapse.
     ) AS "location_2" ON ("person_2"."location_id" = "location_2"."location_id")
     =#
 
+An outer `Join` does not collapse its branches when doing so may change the
+values of unmatched rows.
+
+    join_q(; left = false, right = false) =
+        From(:cohort1) |> Define(:n_cohort => 1) |> As(:cohort1) |>
+        Join(From(:cohort2) |> Define(:n_cohort => 1) |> As(:cohort2),
+             on = Get.cohort1.person_id .== Get.cohort2.person_id,
+             left = left,
+             right = right) |>
+        Select(:person_id => Fun.coalesce(Get.cohort1.person_id, Get.cohort2.person_id),
+               :n_cohort => Fun.coalesce(Get.cohort1.n_cohort, 0) .+ Fun.coalesce(Get.cohort2.n_cohort, 0)) |>
+        With(:cohort1 => From(person) |> Where(Get.year_of_birth .> 1970),
+             :cohort2 => From(person) |> Where(Get.year_of_birth .< 1990))
+
+    print(render(join_q()))
+    #=>
+    WITH "cohort1_1" ("person_id") AS (
+      SELECT "person_1"."person_id"
+      FROM "person" AS "person_1"
+      WHERE ("person_1"."year_of_birth" > 1970)
+    ),
+    "cohort2_1" ("person_id") AS (
+      SELECT "person_2"."person_id"
+      FROM "person" AS "person_2"
+      WHERE ("person_2"."year_of_birth" < 1990)
+    )
+    SELECT
+      coalesce("cohort1_2"."person_id", "cohort2_2"."person_id") AS "person_id",
+      (coalesce(1, 0) + coalesce(1, 0)) AS "n_cohort"
+    FROM "cohort1_1" AS "cohort1_2"
+    JOIN "cohort2_1" AS "cohort2_2" ON ("cohort1_2"."person_id" = "cohort2_2"."person_id")
+    =#
+
+    print(render(join_q(left = true)))
+    #=>
+    WITH "cohort1_1" ("person_id") AS (
+      SELECT "person_1"."person_id"
+      FROM "person" AS "person_1"
+      WHERE ("person_1"."year_of_birth" > 1970)
+    ),
+    "cohort2_1" ("person_id") AS (
+      SELECT "person_2"."person_id"
+      FROM "person" AS "person_2"
+      WHERE ("person_2"."year_of_birth" < 1990)
+    )
+    SELECT
+      coalesce("cohort1_2"."person_id", "cohort2_3"."person_id") AS "person_id",
+      (coalesce(1, 0) + coalesce("cohort2_3"."n_cohort", 0)) AS "n_cohort"
+    FROM "cohort1_1" AS "cohort1_2"
+    LEFT JOIN (
+      SELECT
+        "cohort2_2"."person_id",
+        1 AS "n_cohort"
+      FROM "cohort2_1" AS "cohort2_2"
+    ) AS "cohort2_3" ON ("cohort1_2"."person_id" = "cohort2_3"."person_id")
+    =#
+
+    print(render(join_q(right = true)))
+    #=>
+    WITH "cohort1_1" ("person_id") AS (
+      SELECT "person_1"."person_id"
+      FROM "person" AS "person_1"
+      WHERE ("person_1"."year_of_birth" > 1970)
+    ),
+    "cohort2_1" ("person_id") AS (
+      SELECT "person_2"."person_id"
+      FROM "person" AS "person_2"
+      WHERE ("person_2"."year_of_birth" < 1990)
+    )
+    SELECT
+      coalesce("cohort1_3"."person_id", "cohort2_2"."person_id") AS "person_id",
+      (coalesce("cohort1_3"."n_cohort", 0) + coalesce(1, 0)) AS "n_cohort"
+    FROM (
+      SELECT
+        "cohort1_2"."person_id",
+        1 AS "n_cohort"
+      FROM "cohort1_1" AS "cohort1_2"
+    ) AS "cohort1_3"
+    RIGHT JOIN "cohort2_1" AS "cohort2_2" ON ("cohort1_3"."person_id" = "cohort2_2"."person_id")
+    =#
+
+    print(render(join_q(left = true, right = true)))
+    #=>
+    WITH "cohort1_1" ("person_id") AS (
+      SELECT "person_1"."person_id"
+      FROM "person" AS "person_1"
+      WHERE ("person_1"."year_of_birth" > 1970)
+    ),
+    "cohort2_1" ("person_id") AS (
+      SELECT "person_2"."person_id"
+      FROM "person" AS "person_2"
+      WHERE ("person_2"."year_of_birth" < 1990)
+    )
+    SELECT
+      coalesce("cohort1_3"."person_id", "cohort2_3"."person_id") AS "person_id",
+      (coalesce("cohort1_3"."n_cohort", 0) + coalesce("cohort2_3"."n_cohort", 0)) AS "n_cohort"
+    FROM (
+      SELECT
+        "cohort1_2"."person_id",
+        1 AS "n_cohort"
+      FROM "cohort1_1" AS "cohort1_2"
+    ) AS "cohort1_3"
+    FULL JOIN (
+      SELECT
+        "cohort2_2"."person_id",
+        1 AS "n_cohort"
+      FROM "cohort2_1" AS "cohort2_2"
+    ) AS "cohort2_3" ON ("cohort1_3"."person_id" = "cohort2_3"."person_id")
+    =#
+
 `Join` can be applied to correlated subqueries.
 
     ql(person_id) =

diff --git a/src/translate.jl b/src/translate.jl
@@ -827,9 +827,12 @@ function assemble(n::PartitionNode, ctx)
     Assemblage(base.name, c, cols = cols, repl = repl)
 end
 
+_outer_safe(a::Assemblage) =
+    all(@dissect(col, (nothing |> ID() |> ID())) for col in values(a.cols))
+
 function assemble(n::RoutedJoinNode, ctx)
     left = assemble(n.over, ctx)
-    if @dissect(left.clause, tail := FROM() || JOIN())
+    if @dissect(left.clause, tail := FROM() || JOIN()) && (!n.right || _outer_safe(left))
         left_alias = nothing
     else
         left_alias = allocate_alias(ctx, left)
@@ -842,7 +845,7 @@ function assemble(n::RoutedJoinNode, ctx)
     else
         right = assemble(n.joinee, ctx)
     end
-    if @dissect(right.clause, (joinee := (ID() || AS())) |> FROM())
+    if @dissect(right.clause, (joinee := (ID() || AS())) |> FROM()) && (!n.left || _outer_safe(right))
         for (ref, name) in right.repl
             subs[ref] = right.cols[name]
         end