I am quite new to SQL and I have a need to create a table (TableD)which would contain contents of TableA that do not exist in TableC and combining with contents of TableB that do not exist in TableC. All the tables have same number of columns and also identical column names. Combination of column1,column2 and column3 would give a unique key identifier. TableC contains over 1,000,000 records while TableA and TableB about 2,000,000 and 4,000,000 respectively.
Appreciate if you or other SQL gurus out there can assist me with creating a script to achieve this.