[Q]执行计划顺序是怎么看的？

Execution Plan
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0 SELECT STATEMENT Optimizer=CHOOSE
1 0 SORT (AGGREGATE)
2 1 TABLE ACCESS (BY INDEX ROWID) OF 'USER_INFO'
3 2 NESTED LOOPS
4 3 TABLE ACCESS (FULL) OF 'USER_NUM_TABLE'
5 3 INDEX (RANGE SCAN) OF 'PK_USER_INFO' (UNIQUE)
请问以上执行计划语句是如何看的？语句的执行顺序是什么？为什么？请祥解，多谢！