3 basic oracle questions

Hello, I have an imaginary table tblTest, that will be created in Oracle and defined as below.

CREATE TABLE tblTest(aNUMBER, b NUMBER, c NUMBER, PRIMARY KEY (a), UNIQUE (b,c));

For the purposes of my query, imagine that there are 50 million records in the table, and a value of 'b' is 0 in 10 of the records, and the value of 'c' is 10 in 9 million of the records.

My questions are:
1. Is one of these queries more efficient/quicker than the other?

1. SELECT * FROM tblTest WHERE b=0 AND c=10
2. SELECT * FROM tblTest WHERE c=10 AND b=0
3. Would the query efficiency be different in each case if, during table creation, I had used the query below instead?

CREATE TABLE tblTest(aNUMBER, b NUMBER, c NUMBER, PRIMARY KEY (a), UNIQUE (c,b));

3. UNIQUE is essentially the equivalent to ALTERNATE KEY used by many other DBMS vendors isn't it?

Thank you
David Received on Fri Apr 19 2002 - 13:06:44 CEST