branch-3.0 [cherry-pick](variant) Rename session-var for flatten nested

[amorynan]

What problem does this PR solve?

backport : #54413
Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[Thearas]

Thank you for your contribution to Apache Doris.
Don't know what should be done next? See How to process your PR.

Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[amorynan]

run buildall

[eldenmoon]

LGTM

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.

[hello-stephen]

FE UT Coverage Report

Increment line coverage 50.00% (2/4) 🎉
Increment coverage report
Complete coverage report

[doris-robot]

TPC-H: Total hot run time: 39917 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpch-tools
Tpch sf100 test result on commit dcfc4d4a3ee91a621c444e9af6b5f2a8c497febc, data reload: false

------ Round 1 ----------------------------------
q1	17934	7023	6702	6702
q2	2084	166	160	160
q3	10643	1129	1168	1129
q4	10292	729	698	698
q5	7802	2843	2800	2800
q6	219	137	134	134
q7	992	622	605	605
q8	9348	1946	2011	1946
q9	6630	6407	6437	6407
q10	7018	2227	2345	2227
q11	468	265	265	265
q12	405	215	221	215
q13	17809	3008	3012	3008
q14	238	201	207	201
q15	513	466	457	457
q16	476	383	379	379
q17	985	575	573	573
q18	7276	6757	6713	6713
q19	1411	1029	1024	1024
q20	510	204	208	204
q21	3934	3093	3290	3093
q22	1082	989	977	977
Total cold run time: 108069 ms
Total hot run time: 39917 ms

----- Round 2, with runtime_filter_mode=off -----
q1	6608	6575	6568	6568
q2	327	228	231	228
q3	2879	2898	2962	2898
q4	2024	1867	1834	1834
q5	5686	5731	5695	5695
q6	206	125	132	125
q7	2261	1766	1815	1766
q8	3348	3520	3595	3520
q9	8682	8892	8850	8850
q10	3556	3528	3536	3528
q11	575	493	490	490
q12	799	578	635	578
q13	8931	3209	3156	3156
q14	294	274	274	274
q15	514	473	457	457
q16	492	459	429	429
q17	1840	1630	1612	1612
q18	8265	7733	7868	7733
q19	1665	1372	1574	1372
q20	2066	1819	1894	1819
q21	5234	5052	5071	5052
q22	1183	1098	1023	1023
Total cold run time: 67435 ms
Total hot run time: 59007 ms

[doris-robot]

TPC-DS: Total hot run time: 197660 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpcds-tools
TPC-DS sf100 test result on commit dcfc4d4a3ee91a621c444e9af6b5f2a8c497febc, data reload: false

query1	1286	972	918	918
query2	6236	1982	1940	1940
query3	10935	4480	4596	4480
query4	32946	23653	23360	23360
query5	3413	454	455	454
query6	269	186	189	186
query7	3991	318	336	318
query8	308	244	236	236
query9	9374	2577	2569	2569
query10	479	263	257	257
query11	17942	15232	15668	15232
query12	163	103	106	103
query13	1553	423	424	423
query14	9600	7223	6697	6697
query15	236	187	199	187
query16	8005	506	464	464
query17	1630	585	602	585
query18	2200	335	337	335
query19	251	181	164	164
query20	122	114	113	113
query21	212	117	108	108
query22	4851	4614	4519	4519
query23	34934	34444	34479	34444
query24	11694	2966	2891	2891
query25	652	443	419	419
query26	1216	179	166	166
query27	2567	364	346	346
query28	7349	2150	2168	2150
query29	857	432	441	432
query30	272	169	159	159
query31	1030	832	866	832
query32	100	63	55	55
query33	760	298	302	298
query34	1055	521	530	521
query35	864	768	715	715
query36	1115	957	958	957
query37	118	69	67	67
query38	4043	3939	4005	3939
query39	1515	1493	1509	1493
query40	204	97	103	97
query41	52	50	51	50
query42	119	108	107	107
query43	530	482	488	482
query44	1504	822	828	822
query45	188	178	173	173
query46	1155	754	741	741
query47	2017	1922	1921	1921
query48	469	384	381	381
query49	987	400	410	400
query50	868	448	433	433
query51	7430	7254	7241	7241
query52	106	95	96	95
query53	267	191	186	186
query54	1272	467	478	467
query55	85	80	80	80
query56	268	267	272	267
query57	1299	1248	1198	1198
query58	232	218	213	213
query59	3201	3165	3055	3055
query60	298	271	272	271
query61	117	131	113	113
query62	843	690	708	690
query63	235	194	195	194
query64	4019	713	640	640
query65	3361	3305	3281	3281
query66	883	311	298	298
query67	16278	15715	15613	15613
query68	4653	585	580	580
query69	439	262	263	262
query70	1157	1097	1147	1097
query71	362	262	262	262
query72	6308	4080	4034	4034
query73	761	349	354	349
query74	10509	9020	8994	8994
query75	3298	2652	2689	2652
query76	2673	1135	1156	1135
query77	407	282	277	277
query78	10488	9633	9564	9564
query79	1257	606	591	591
query80	1079	469	431	431
query81	545	222	218	218
query82	1048	88	91	88
query83	236	144	148	144
query84	231	78	80	78
query85	1307	301	309	301
query86	392	293	283	283
query87	4381	4284	4178	4178
query88	3660	2389	2371	2371
query89	400	303	285	285
query90	1869	188	189	188
query91	186	152	153	152
query92	64	52	51	51
query93	1241	561	566	561
query94	821	315	317	315
query95	363	266	266	266
query96	596	281	279	279
query97	3284	3120	3214	3120
query98	216	208	198	198
query99	1535	1326	1315	1315
Total cold run time: 300196 ms
Total hot run time: 197660 ms

[doris-robot]

ClickBench: Total hot run time: 30.79 s

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/clickbench-tools
ClickBench test result on commit dcfc4d4a3ee91a621c444e9af6b5f2a8c497febc, data reload: false

query1	0.03	0.03	0.04
query2	0.06	0.03	0.03
query3	0.23	0.07	0.06
query4	1.62	0.11	0.11
query5	0.51	0.51	0.53
query6	1.14	0.74	0.73
query7	0.02	0.02	0.02
query8	0.04	0.03	0.04
query9	0.55	0.52	0.51
query10	0.55	0.57	0.55
query11	0.15	0.10	0.10
query12	0.13	0.11	0.11
query13	0.61	0.60	0.60
query14	0.77	0.78	0.79
query15	0.84	0.82	0.82
query16	0.41	0.37	0.39
query17	1.02	1.08	1.09
query18	0.24	0.22	0.22
query19	1.96	1.87	1.86
query20	0.02	0.02	0.01
query21	15.37	0.58	0.56
query22	2.45	1.72	1.85
query23	16.84	1.18	0.77
query24	2.91	1.80	1.48
query25	0.23	0.19	0.08
query26	0.52	0.14	0.14
query27	0.06	0.04	0.06
query28	9.44	0.54	0.49
query29	12.54	3.28	3.24
query30	0.25	0.07	0.07
query31	2.83	0.38	0.38
query32	3.30	0.46	0.45
query33	3.01	3.00	3.02
query34	16.94	4.52	4.52
query35	4.56	4.54	4.53
query36	0.68	0.48	0.48
query37	0.08	0.06	0.06
query38	0.05	0.04	0.04
query39	0.03	0.02	0.02
query40	0.16	0.12	0.13
query41	0.08	0.02	0.03
query42	0.03	0.02	0.02
query43	0.04	0.03	0.03
Total cold run time: 103.3 s
Total hot run time: 30.79 s

[amorynan]

run buildall

[doris-robot]

TPC-H: Total hot run time: 40023 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpch-tools
Tpch sf100 test result on commit 386f3222476993e6d59d3e406d3cb9f633e3ed5a, data reload: false

------ Round 1 ----------------------------------
q1	17600	7026	6729	6729
q2	2072	171	182	171
q3	10600	1129	1145	1129
q4	10227	752	701	701
q5	7742	2947	2796	2796
q6	224	139	141	139
q7	976	627	613	613
q8	9381	1999	2106	1999
q9	6661	6454	6419	6419
q10	7053	2270	2275	2270
q11	462	265	264	264
q12	411	214	214	214
q13	17797	3027	2997	2997
q14	238	215	213	213
q15	507	476	468	468
q16	508	381	374	374
q17	1004	619	570	570
q18	7417	6608	6587	6587
q19	1407	1090	1027	1027
q20	477	205	209	205
q21	4064	3159	3257	3159
q22	1075	979	997	979
Total cold run time: 107903 ms
Total hot run time: 40023 ms

----- Round 2, with runtime_filter_mode=off -----
q1	6660	6637	6612	6612
q2	327	237	237	237
q3	2964	2969	2949	2949
q4	2066	1824	1843	1824
q5	5750	5765	5721	5721
q6	214	130	130	130
q7	2206	1805	1846	1805
q8	3398	3551	3595	3551
q9	8798	8887	8837	8837
q10	3573	3534	3547	3534
q11	588	493	491	491
q12	852	604	616	604
q13	9554	3201	3166	3166
q14	310	282	283	282
q15	508	475	466	466
q16	496	435	422	422
q17	1868	1641	1615	1615
q18	8385	7825	7669	7669
q19	1736	1728	1476	1476
q20	2059	1828	1819	1819
q21	5305	5199	4974	4974
q22	1161	1059	992	992
Total cold run time: 68778 ms
Total hot run time: 59176 ms

[doris-robot]

TPC-DS: Total hot run time: 197560 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpcds-tools
TPC-DS sf100 test result on commit 386f3222476993e6d59d3e406d3cb9f633e3ed5a, data reload: false

query1	1277	974	915	915
query2	6315	1971	1925	1925
query3	10943	4384	4572	4384
query4	33254	23629	23864	23629
query5	4445	487	472	472
query6	286	189	193	189
query7	3996	321	323	321
query8	298	245	237	237
query9	9567	2596	2580	2580
query10	490	277	262	262
query11	17988	15230	15178	15178
query12	159	106	102	102
query13	1553	442	418	418
query14	9858	6817	7815	6817
query15	257	186	197	186
query16	8037	479	473	473
query17	1654	581	610	581
query18	2155	324	316	316
query19	347	155	176	155
query20	126	117	126	117
query21	209	105	110	105
query22	4878	4434	4413	4413
query23	35284	34241	33962	33962
query24	11968	3002	3052	3002
query25	653	410	399	399
query26	1755	173	171	171
query27	2853	352	360	352
query28	7744	2150	2164	2150
query29	1019	439	471	439
query30	252	167	157	157
query31	1045	818	834	818
query32	91	58	55	55
query33	762	313	314	313
query34	1155	505	536	505
query35	925	776	752	752
query36	1148	972	974	972
query37	259	88	70	70
query38	4143	4034	4032	4032
query39	1499	1465	1478	1465
query40	254	104	103	103
query41	54	51	51	51
query42	136	102	101	101
query43	531	481	489	481
query44	1360	821	836	821
query45	193	177	166	166
query46	1151	722	740	722
query47	1989	1923	1957	1923
query48	488	408	393	393
query49	1102	394	402	394
query50	854	454	446	446
query51	7338	7259	7242	7242
query52	108	100	96	96
query53	259	192	189	189
query54	1337	484	476	476
query55	83	77	81	77
query56	291	251	271	251
query57	1341	1239	1201	1201
query58	242	225	224	224
query59	3278	3213	3001	3001
query60	327	283	277	277
query61	139	136	136	136
query62	861	721	712	712
query63	229	202	200	200
query64	5221	805	777	777
query65	3437	3248	3227	3227
query66	1298	318	306	306
query67	15843	15924	15711	15711
query68	4823	587	585	585
query69	440	275	280	275
query70	1202	1156	1130	1130
query71	332	262	276	262
query72	6327	4056	3875	3875
query73	770	359	358	358
query74	10280	9279	9058	9058
query75	3360	2615	2747	2615
query76	2646	1080	1131	1080
query77	387	280	269	269
query78	10569	9516	9502	9502
query79	2360	619	628	619
query80	1098	436	446	436
query81	545	220	220	220
query82	687	85	90	85
query83	245	150	142	142
query84	236	80	76	76
query85	1595	345	295	295
query86	473	314	307	307
query87	4360	4240	4235	4235
query88	4324	2488	2364	2364
query89	416	297	295	295
query90	1986	189	185	185
query91	186	148	148	148
query92	61	51	49	49
query93	2184	569	569	569
query94	883	304	291	291
query95	359	263	264	263
query96	611	277	276	276
query97	3271	3180	3117	3117
query98	227	208	192	192
query99	1532	1303	1294	1294
Total cold run time: 309166 ms
Total hot run time: 197560 ms

[doris-robot]

ClickBench: Total hot run time: 30.16 s

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/clickbench-tools
ClickBench test result on commit 386f3222476993e6d59d3e406d3cb9f633e3ed5a, data reload: false

query1	0.03	0.03	0.02
query2	0.07	0.03	0.03
query3	0.23	0.07	0.07
query4	1.61	0.11	0.10
query5	0.52	0.49	0.52
query6	1.12	0.73	0.73
query7	0.02	0.02	0.01
query8	0.04	0.03	0.03
query9	0.56	0.50	0.50
query10	0.54	0.55	0.55
query11	0.14	0.10	0.11
query12	0.14	0.11	0.11
query13	0.61	0.60	0.61
query14	0.77	0.81	0.79
query15	0.85	0.83	0.83
query16	0.38	0.38	0.41
query17	1.06	1.08	1.08
query18	0.24	0.21	0.21
query19	1.90	1.82	1.91
query20	0.01	0.01	0.01
query21	15.43	0.56	0.58
query22	2.17	1.86	1.72
query23	17.15	0.94	0.71
query24	3.60	1.53	0.95
query25	0.26	0.12	0.14
query26	0.48	0.14	0.13
query27	0.05	0.04	0.04
query28	9.71	0.50	0.48
query29	12.59	3.26	3.28
query30	0.24	0.07	0.06
query31	2.86	0.38	0.39
query32	3.23	0.46	0.45
query33	3.02	2.99	3.04
query34	16.93	4.54	4.51
query35	4.54	4.57	4.59
query36	0.67	0.50	0.47
query37	0.08	0.06	0.06
query38	0.05	0.04	0.03
query39	0.04	0.02	0.03
query40	0.16	0.13	0.12
query41	0.08	0.02	0.03
query42	0.04	0.02	0.02
query43	0.04	0.04	0.03
Total cold run time: 104.26 s
Total hot run time: 30.16 s

[hello-stephen]

FE UT Coverage Report

Increment line coverage 60.00% (3/5) 🎉
Increment coverage report
Complete coverage report

[eldenmoon]

LGTM

[github-actions]

PR approved by at least one committer and no changes requested.

[eldenmoon]

LGTM

[dataroaring]

LGTM

[amorynan]

run buildall

[eldenmoon]

run buildall

[eldenmoon]

LGTM

[doris-robot]

TPC-H: Total hot run time: 39749 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpch-tools
Tpch sf100 test result on commit 7cfdbedff87094596dd263599ee1fc1dbd622f26, data reload: false

------ Round 1 ----------------------------------
q1	17594	6693	6662	6662
q2	2057	182	161	161
q3	10680	1112	1087	1087
q4	10436	712	675	675
q5	7749	2823	2775	2775
q6	208	129	132	129
q7	978	631	617	617
q8	9367	1933	2008	1933
q9	6664	6406	6380	6380
q10	7020	2292	2327	2292
q11	470	266	258	258
q12	421	215	208	208
q13	17778	2998	2968	2968
q14	232	211	213	211
q15	505	466	452	452
q16	484	389	367	367
q17	957	539	539	539
q18	7334	6690	6762	6690
q19	1431	1071	1059	1059
q20	480	195	217	195
q21	4117	3091	3097	3091
q22	1113	1006	1000	1000
Total cold run time: 108075 ms
Total hot run time: 39749 ms

----- Round 2, with runtime_filter_mode=off -----
q1	6627	6549	6573	6549
q2	340	239	228	228
q3	2891	2901	2898	2898
q4	2052	1870	1816	1816
q5	5719	5728	5705	5705
q6	211	129	128	128
q7	2258	1817	1829	1817
q8	3353	3495	3557	3495
q9	8780	8948	8841	8841
q10	3570	3478	3495	3478
q11	584	497	503	497
q12	804	624	608	608
q13	8380	3260	3147	3147
q14	301	265	259	259
q15	501	472	471	471
q16	492	443	441	441
q17	1851	1627	1618	1618
q18	8384	7699	7821	7699
q19	1689	1539	1486	1486
q20	2104	1912	1927	1912
q21	5331	5229	5104	5104
q22	1152	1083	1019	1019
Total cold run time: 67374 ms
Total hot run time: 59216 ms

[doris-robot]

TPC-DS: Total hot run time: 195356 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpcds-tools
TPC-DS sf100 test result on commit 7cfdbedff87094596dd263599ee1fc1dbd622f26, data reload: false

query1	1300	950	906	906
query2	6296	1879	1909	1879
query3	10948	4349	4552	4349
query4	33394	23388	23434	23388
query5	3575	449	450	449
query6	264	172	173	172
query7	4001	313	314	313
query8	282	224	222	222
query9	9436	2563	2554	2554
query10	484	262	248	248
query11	17926	15079	15376	15079
query12	167	105	107	105
query13	1555	430	414	414
query14	9260	7026	7280	7026
query15	252	177	195	177
query16	7968	490	524	490
query17	1649	610	579	579
query18	2108	327	313	313
query19	252	167	160	160
query20	123	117	113	113
query21	213	111	111	111
query22	4920	4563	4664	4563
query23	35481	34083	34148	34083
query24	11385	2983	3006	2983
query25	669	439	429	429
query26	908	175	174	174
query27	2149	370	354	354
query28	6736	2167	2156	2156
query29	827	461	476	461
query30	276	162	159	159
query31	1035	825	848	825
query32	109	53	57	53
query33	765	291	309	291
query34	1129	516	507	507
query35	885	721	738	721
query36	1146	913	943	913
query37	116	65	68	65
query38	4156	3944	3964	3944
query39	1530	1516	1442	1442
query40	210	103	101	101
query41	50	49	48	48
query42	119	116	96	96
query43	508	488	491	488
query44	1240	815	816	815
query45	206	170	175	170
query46	1171	710	737	710
query47	2034	1941	1943	1941
query48	483	373	389	373
query49	904	397	395	395
query50	848	416	440	416
query51	7401	7300	7300	7300
query52	97	86	93	86
query53	256	183	184	183
query54	1254	455	462	455
query55	81	81	83	81
query56	263	239	258	239
query57	1330	1242	1228	1228
query58	230	215	211	211
query59	3160	2911	2957	2911
query60	292	251	250	250
query61	122	111	113	111
query62	860	671	704	671
query63	221	188	185	185
query64	4123	703	636	636
query65	3305	3294	3333	3294
query66	808	301	299	299
query67	16011	15604	15830	15604
query68	4421	574	576	574
query69	435	266	266	266
query70	1172	1134	1117	1117
query71	330	247	264	247
query72	6279	2583	3870	2583
query73	754	343	356	343
query74	10449	8930	9008	8930
query75	3371	2633	2661	2633
query76	2671	1002	1037	1002
query77	373	293	271	271
query78	10515	9703	9620	9620
query79	2374	606	592	592
query80	1217	418	412	412
query81	552	222	211	211
query82	690	88	86	86
query83	228	140	141	140
query84	235	83	84	83
query85	1673	306	282	282
query86	484	306	300	300
query87	4440	4263	4218	4218
query88	4310	2346	2346	2346
query89	412	290	291	290
query90	1930	186	186	186
query91	181	147	149	147
query92	63	51	49	49
query93	2434	551	550	550
query94	843	299	275	275
query95	353	252	248	248
query96	618	275	280	275
query97	3297	3151	3136	3136
query98	213	195	195	195
query99	1525	1282	1298	1282
Total cold run time: 302104 ms
Total hot run time: 195356 ms

[doris-robot]

ClickBench: Total hot run time: 30.37 s

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/clickbench-tools
ClickBench test result on commit 7cfdbedff87094596dd263599ee1fc1dbd622f26, data reload: false

query1	0.04	0.03	0.03
query2	0.07	0.03	0.02
query3	0.23	0.06	0.06
query4	1.62	0.11	0.10
query5	0.50	0.49	0.51
query6	1.13	0.72	0.74
query7	0.02	0.02	0.02
query8	0.04	0.03	0.03
query9	0.56	0.49	0.49
query10	0.55	0.54	0.55
query11	0.14	0.09	0.09
query12	0.14	0.11	0.11
query13	0.61	0.59	0.60
query14	0.77	0.81	0.80
query15	0.83	0.82	0.81
query16	0.40	0.38	0.40
query17	1.06	1.09	1.02
query18	0.25	0.22	0.22
query19	1.97	1.74	1.85
query20	0.01	0.01	0.02
query21	15.40	0.59	0.59
query22	2.21	2.09	1.69
query23	16.82	0.90	0.90
query24	3.00	1.19	1.67
query25	0.32	0.13	0.10
query26	0.38	0.13	0.14
query27	0.04	0.04	0.04
query28	9.65	0.50	0.49
query29	12.59	3.26	3.25
query30	0.25	0.06	0.06
query31	2.86	0.39	0.39
query32	3.25	0.45	0.46
query33	2.98	3.06	2.99
query34	17.17	4.63	4.49
query35	4.56	4.56	4.55
query36	0.66	0.48	0.48
query37	0.08	0.06	0.06
query38	0.04	0.03	0.04
query39	0.03	0.02	0.02
query40	0.16	0.13	0.13
query41	0.07	0.02	0.03
query42	0.03	0.02	0.02
query43	0.04	0.03	0.03
Total cold run time: 103.53 s
Total hot run time: 30.37 s

[dataroaring]

LGTM