Oracle SQL Tuning

Hi,

I got two data structure identifical tables table_a and table_b. Table table_a contains not more than 100 records while Table table_b contains more than 100000 records. Both tables have the same Primary Key.

Now, I am going to "diff" the records in table_a with the ones in table_b and show the different records in table_a. Someone told me that I could use the following SQL statement to "diff" the records :

SELECT * FROM table_a

MINUS SELECT * FROM table_b

He told me that it was efficient to find the difference of the two identificals. As I have not used this way to compare two sets of records, I went ahead to run the SQL statement. However, I found that the above SQL statement ran a long long time, even though the number

Can the above statement use the Primary Key as indexing?

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Regards,

Patrick Lo