Start to implement database transaction tree

script/sql/create/operation.sql

@@ -0,0 +1,17 @@
+CREATE TABLE OPERATION
+(
+  ID SERIAL PRIMARY KEY
+, REDO TEXT NOT NULL
+, UNDO TEXT NOT NULL
+, PARENT INTEGER REFERENCES OPERATION(ID)
+, REDOCHILD INTEGER REFERENCES OPERATION(ID)
+);
+
+INSERT INTO OPERATION (ID, REDO, UNDO) VALUES (0, '', '');
+
+CREATE TABLE CURRENTOPERATION
+(
+  ID INTEGER PRIMARY KEY REFERENCES OPERATION(ID)
+);
+
+INSERT INTO CURRENTOPERATION (ID) VALUES (0);

script/sql/drop/operation.sql

@@ -0,0 +1,3 @@
+DROP TABLE CURRENTOPERATION;
+
+DROP TABLE OPERATION;