Oracle SQL Execution Plan Difference - sql

Question

I have the below query and I'm generating the execution plan for it:
(EDIT: I'm using SQL Developer).
EXPLAIN PLAN
FOR
WITH aux AS (
SELECT
*
FROM
cdc.uap_fkkvkp#rbip
WHERE
ezawe = 'D'
)
SELECT /* FULL(a) FULL(b) */
-- COUNT(1)
b.zzpayment_plan,
b.vkont,
b.gpart,
a.opbel,
a.opupw,
a.opupk,
a.opupz,
a.blart,
a.betrw
FROM
cdc.uap_dfkkop#rbip a
JOIN aux b ON b.vkont = a.vkont
WHERE
a.augst IS NULL
AND a.xanza IS NULL
AND a.stakz IS NULL
AND a.augrs IS NULL
AND a.abwtp IS NULL;
SELECT
*
FROM
TABLE ( dbms_xplan.display );
It gives the below plan:
Plan hash value: 289441478
-----------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4404K| 634M| | 6752K (1)| 00:04:24 |
|* 1 | HASH JOIN | | 4404K| 634M| 291M| 6752K (1)| 00:04:24 |
|* 2 | TABLE ACCESS STORAGE FULL | UAP_FKKVKP | 4487K| 239M| | 559K (1)| 00:00:22 |
|* 3 | TABLE ACCESS BY INDEX ROWID BATCHED| UAP_DFKKOP | 4404K| 399M| | 6160K (1)| 00:04:01 |
| 4 | BITMAP CONVERSION TO ROWIDS | | | | | | |
| 5 | BITMAP AND | | | | | | |
|* 6 | BITMAP INDEX SINGLE VALUE | UAP_DFKKOP_AUGST_2 | | | | | |
|* 7 | BITMAP INDEX SINGLE VALUE | UAP_DFKKOP_NEW_STAKZ_2 | | | | | |
|* 8 | BITMAP INDEX SINGLE VALUE | UAP_DFKKOP_AUGRS_2 | | | | | |
-----------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("UAP_FKKVKP"."VKONT"="A"."VKONT")
2 - storage("EZAWE"=U'D')
filter("EZAWE"=U'D')
3 - filter("A"."XANZA" IS NULL AND "A"."ABWTP" IS NULL)
6 - access("A"."AUGST" IS NULL)
7 - access("A"."STAKZ" IS NULL)
8 - access("A"."AUGRS" IS NULL)
Note
-----
- dynamic statistics used: dynamic sampling (level=2)
- 1 Sql Plan Directive used for this statement
However, if I generate the plan for the first part of the code, but for the COUNT(1) uncommented (and the other selections commented), the below shows (it's exactly the same as the previous execution plan):
Plan hash value: 2732266276
------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time |
------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 66 | | 6736K (1)| 00:04:24 |
| 1 | SORT AGGREGATE | | 1 | 66 | | | |
|* 2 | HASH JOIN | | 4404K| 277M| 171M| 6736K (1)| 00:04:24 |
|* 3 | TABLE ACCESS STORAGE FULL | UAP_FKKVKP | 4487K| 119M| | 559K (1)| 00:00:22 |
|* 4 | TABLE ACCESS BY INDEX ROWID BATCHED| UAP_DFKKOP | 4404K| 159M| | 6160K (1)| 00:04:01 |
| 5 | BITMAP CONVERSION TO ROWIDS | | | | | | |
| 6 | BITMAP AND | | | | | | |
|* 7 | BITMAP INDEX SINGLE VALUE | UAP_DFKKOP_AUGST_2 | | | | | |
|* 8 | BITMAP INDEX SINGLE VALUE | UAP_DFKKOP_NEW_STAKZ_2 | | | | | |
|* 9 | BITMAP INDEX SINGLE VALUE | UAP_DFKKOP_AUGRS_2 | | | | | |
------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("UAP_FKKVKP"."VKONT"="A"."VKONT")
3 - storage("EZAWE"=U'D')
filter("EZAWE"=U'D')
4 - filter("A"."XANZA" IS NULL AND "A"."ABWTP" IS NULL)
7 - access("A"."AUGST" IS NULL)
8 - access("A"."STAKZ" IS NULL)
9 - access("A"."AUGRS" IS NULL)
Note
-----
- dynamic statistics used: dynamic sampling (level=2)
- 1 Sql Plan Directive used for this statement
If I try to execute both queries, the first one takes about 3 secs while the second one takes almost 8 mins.
Why is there such a difference between the two and why is it not captured in the execution plan?
Is my full table scan here correctly applied? If not, what would be the best hint?
What would be the best (up to date) book/documentation/online tutorials to upgrade my SQL performance skills? So far, I've seen that Oracle has a dev gym for performance and there are also some books like Advanced Oracle SQL Tuning which looks interesting.

Answer 1

With explain there is no real execution. You will receive a lot more details with real execution after turning statistics_level to ALL on session level.
But run it in SQLPLUS:
set serverout off
alter session set statistics_level=all;
<execute the query here without explain>
select * from table(dbms_xplan.display_cursor(null,null,'RUNSTATS_LAST'));
If you provide two such plans instead of EXPLAIN PLAN it will be easier for your readers.
Short description of important columns(Tanel Poder site is good):
Starts - number of execution of the step
A-Rows - actual number of rows received from this step
Buffers - number of reads from RAM - you have to decrease this value
Reads - number of reads from disk
Writes - number of writes to disk - different from 0 - mainly for SELECTs when TEMP is used
This method for plan usage is shown for example here : https://tanelpoder.com/files/Oracle_SQL_Plan_Execution.pdf