感觉不到差别：
CREATE TABLE TEST1 AS SELECT OBJECT_ID N, TO_CHAR(OBJECT_ID) S FROM ALL_OBJECTS;
CREATE TABLE TEST2 AS SELECT OBJECT_ID N, TO_CHAR(OBJECT_ID) S FROM ALL_OBJECTS;
SELECT COUNT(*) FROM TEST1,TEST2 WHERE TEST1.N=TEST2.N;
COUNT(*)
----------
72349
Elapsed: 00:00:00.83
/
COUNT(*)
----------
72349
Elapsed: 00:00:00.04
SELECT COUNT(*) FROM TEST1,TEST2 WHERE TEST1.S=TEST2.S;
COUNT(*)
----------
72349
Elapsed: 00:00:00.11
/
COUNT(*)
----------
72349
Elapsed: 00:00:00.05
把字符串变得长一点，还是没有显著变化：
UPDATE TEST1 SET S=S||S||S||S;
UPDATE TEST2 SET S=S||S||S||S;
COUNT(*)
----------
72349
SELECT COUNT(*) FROM TEST1,TEST2 WHERE TEST1.S=TEST2.S;
Elapsed: 00:00:00.06
