From 3b3888e9be75662b71468a79ba65f47da7819877 Mon Sep 17 00:00:00 2001
From: Salvo 'LtWorf' Tomaselli <tiposchi@tiscali.it>
Date: Sun, 3 Jan 2016 10:07:23 +0100
Subject: [PATCH] New optimization
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Turns
        π a,b,c(A) ∪ π a,b,c(B)

    into
        π a,b,c(A ∪ B)

    if A and B are union compatible

Works with union, intersection and difference.
---
 CHANGELOG                    |  2 +-
 relational/optimizations.py  | 40 ++++++++++++++++++++++++++++++++++--
 test/union_projection.query  |  1 +
 test/union_projection.result |  8 ++++++++
 4 files changed, 48 insertions(+), 3 deletions(-)
 create mode 100644 test/union_projection.query
 create mode 100644 test/union_projection.result

diff --git a/CHANGELOG b/CHANGELOG
index 3ac9898..83c65bb 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -2,7 +2,7 @@
 - Added again make install target
 - Ctrl+C in the terminal will terminate the GUI
 - UI indicates ongoing processing with a label
-- Added new optimization
+- Added new optimizations
 - Added shortcuts within the UI
 - History can be navigated with up/down arrows
 - Single line edit mode allows for the resulting relation to be written
diff --git a/relational/optimizations.py b/relational/optimizations.py
index 489fee0..5eb2320 100644
--- a/relational/optimizations.py
+++ b/relational/optimizations.py
@@ -544,6 +544,39 @@ def union_and_product(n):
             changes = 1
     return changes + recoursive_scan(union_and_product, n)
 
+def projection_and_union(n, rels):
+    '''
+    Turns
+        π a,b,c(A) ∪ π a,b,c(B)
+
+    into
+        π a,b,c(A ∪ B)
+
+    if A and B are union compatible
+    '''
+    changes = 0
+    if n.name in {UNION, INTERSECTION, DIFFERENCE} and \
+            n.left.name == PROJECTION and \
+            n.right.name == PROJECTION and \
+            set(n.left.result_format(rels)) == set(n.right.result_format(rels)) and \
+            set(n.left.child.result_format(rels)) == set(n.right.child.result_format(rels)):
+        newchild = parser.Node()
+
+        newchild.kind = parser.BINARY
+        newchild.name = n.name
+        newchild.left = n.left.child
+        newchild.right = n.right.child
+
+        newnode = parser.Node()
+        newnode.child = newchild
+        newnode.kind = parser.UNARY
+        newnode.name = PROJECTION
+        newnode.prop = n.right.prop
+        replace_node(n, newnode)
+        changes = 1
+    return changes + recoursive_scan(projection_and_union, n, rels)
+
+
 
 def selection_and_product(n, rels):
     '''This function locates things like σ k (R*Q) and converts them into
@@ -653,9 +686,12 @@ general_optimizations = [
     swap_union_renames,
     swap_rename_projection,
     select_union_intersect_subtract,
-    union_and_product
+    union_and_product,
+]
+specific_optimizations = [
+    selection_and_product,
+    projection_and_union,
 ]
-specific_optimizations = [selection_and_product]
 
 if __name__ == "__main__":
     print (tokenize_select("skill == 'C' and  id % 2 == 0"))
diff --git a/test/union_projection.query b/test/union_projection.query
new file mode 100644
index 0000000..251af9e
--- /dev/null
+++ b/test/union_projection.query
@@ -0,0 +1 @@
+πname,skill(σ skill == 'Perl' (people⋈skills)) ∪ πname,skill(σ skill == 'C' (people⋈skills))
diff --git a/test/union_projection.result b/test/union_projection.result
new file mode 100644
index 0000000..7e0ab5d
--- /dev/null
+++ b/test/union_projection.result
@@ -0,0 +1,8 @@
+name,skill
+jack,C
+eve,Perl
+duncan,Perl
+duncan,C
+john,C
+alia,C
+eve,C