WHERE vs. ON clause conditions with dif't result sets, PostgreSQL

WHERE vs. ON clause conditions with dif't result sets

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CREATE TABLE main_sys (hist_id varchar(5), master_id_sysA varchar(4), master_id_sysB varchar(4), loc_desc varchar(30), curr_flag int, eff_start_dt date, eff_end_dt date);
INSERT INTO main_sys (hist_id,master_id_sysA,master_id_sysB,loc_desc,curr_flag,eff_start_dt,eff_end_dt) VALUES
('14001','1234','1234','Detroit, MI',0,'05/31/2015','07/22/2016')
,('14002','1234','1234','Detroit, MI',0,'07/23/2016','09/01/2016')
,('14005','1234','1234','Detroit, MI',0,'09/02/2016','01/05/2017')
,('14009','1234','1234','Detroit, MI',0,'01/06/2017','07/01/2017')
,('14009','1234','1234','Detroit, MI',1,'07/02/2017','01/01/9999')
,('39002','9987','9987','Atlanta, GA',0,'01/06/2016','07/05/2016')
,('39003','9987','9987','Atlanta, GA',0,'07/06/2016','09/22/2016')
,('39007','9987','9987','Atlanta, GA',0,'09/23/2016','10/31/2016')
,('39014','9987','9987','Atlanta, GA',0,'11/01/2016','06/04/2017')
,('39014','9987','9987','Atlanta, GA',1,'06/05/2017','01/01/9999')
,('90012','6655','6655','Dover, DE',0,'05/31/2015','05/31/2015')
,('90030','6655','6655','Dover, DE',0,'06/01/2015','06/01/2015')
,('90088','6655','6655','Dover, DE',1,'06/02/2015','06/21/2015')
,('14145','9595','9595','Boston, MA',1,'09/09/2006','10/10/2014')
,('14412','8877','0877','Austin, TX',0,'02/16/2017','02/17/2017')
,('14413','8877','0877',NULL,0,'02/18/2017','06/18/2017')
,('14413','8877',NULL,NULL,0,'06/19/2017','08/02/2017')
,('14412','8877','0877','Austin, TX',0,'08/03/2017','09/01/2017')
,('14413','8877',NULL,NULL,1,'09/02/2017','12/31/9999')
;

CREATE TABLE integrated_sys (loc_name varchar(30), master_id_sysA varchar(4), master_id_sysB varchar(4));
INSERT INTO integrated_sys (loc_name,master_id_sysA,master_id_sysB) VALUES
('Detroit, MI','1234','1234')
,('Atlanta, GA','9987','9987')
,('Dover, DE','6655','6655')
,('Boston, MA','NULL','9595')
,('Tempe, AZ','NULL','55')
,('Seattle, OR','NULL','95')
,('Des Moines, IO','NULL','1478')
,('Bismarck, SD','NULL','1515');

-- WHAT IS THE DIFFERENCE BETWEEN THESE TWO QUERIES?
select 
    * 
from 
    main_sys m
    left join integrated_sys i  on (m.master_id_sysa = i.master_id_sysa or m.master_id_sysb = i.master_id_sysb)
where
    m.curr_flag = 1
;

select 
    * 
from 
    main_sys m
    left join integrated_sys i  on ((m.master_id_sysa = i.master_id_sysa or m.master_id_sysb = i.master_id_sysb) and m.curr_flag = 1)
;


absolute service time: 0,48 sec

	hist_id	master_id_sysa	master_id_sysb	loc_desc	curr_flag	eff_start_dt	eff_end_dt	loc_name	master_id_sysa	master_id_sysb
1	14009	1234	1234	Detroit, MI	1	02.07.2017 00:00:00	01.01.9999 00:00:00	Detroit, MI	1234	1234
2	39014	9987	9987	Atlanta, GA	1	05.06.2017 00:00:00	01.01.9999 00:00:00	Atlanta, GA	9987	9987
3	90088	6655	6655	Dover, DE	1	02.06.2015 00:00:00	21.06.2015 00:00:00	Dover, DE	6655	6655
4	14145	9595	9595	Boston, MA	1	09.09.2006 00:00:00	10.10.2014 00:00:00	Boston, MA	NULL	9595
5	14413	8877	NULL	NULL	1	02.09.2017 00:00:00	31.12.9999 00:00:00	NULL	NULL	NULL

	hist_id	master_id_sysa	master_id_sysb	loc_desc	curr_flag	eff_start_dt	eff_end_dt	loc_name	master_id_sysa	master_id_sysb
1	14001	1234	1234	Detroit, MI	0	31.05.2015 00:00:00	22.07.2016 00:00:00	NULL	NULL	NULL
2	14002	1234	1234	Detroit, MI	0	23.07.2016 00:00:00	01.09.2016 00:00:00	NULL	NULL	NULL
3	14005	1234	1234	Detroit, MI	0	02.09.2016 00:00:00	05.01.2017 00:00:00	NULL	NULL	NULL
4	14009	1234	1234	Detroit, MI	0	06.01.2017 00:00:00	01.07.2017 00:00:00	NULL	NULL	NULL
5	14009	1234	1234	Detroit, MI	1	02.07.2017 00:00:00	01.01.9999 00:00:00	Detroit, MI	1234	1234
6	39002	9987	9987	Atlanta, GA	0	06.01.2016 00:00:00	05.07.2016 00:00:00	NULL	NULL	NULL
7	39003	9987	9987	Atlanta, GA	0	06.07.2016 00:00:00	22.09.2016 00:00:00	NULL	NULL	NULL
8	39007	9987	9987	Atlanta, GA	0	23.09.2016 00:00:00	31.10.2016 00:00:00	NULL	NULL	NULL
9	39014	9987	9987	Atlanta, GA	0	01.11.2016 00:00:00	04.06.2017 00:00:00	NULL	NULL	NULL
10	39014	9987	9987	Atlanta, GA	1	05.06.2017 00:00:00	01.01.9999 00:00:00	Atlanta, GA	9987	9987
11	90012	6655	6655	Dover, DE	0	31.05.2015 00:00:00	31.05.2015 00:00:00	NULL	NULL	NULL
12	90030	6655	6655	Dover, DE	0	01.06.2015 00:00:00	01.06.2015 00:00:00	NULL	NULL	NULL
13	90088	6655	6655	Dover, DE	1	02.06.2015 00:00:00	21.06.2015 00:00:00	Dover, DE	6655	6655
14	14145	9595	9595	Boston, MA	1	09.09.2006 00:00:00	10.10.2014 00:00:00	Boston, MA	NULL	9595
15	14412	8877	0877	Austin, TX	0	16.02.2017 00:00:00	17.02.2017 00:00:00	NULL	NULL	NULL
16	14413	8877	0877	NULL	0	18.02.2017 00:00:00	18.06.2017 00:00:00	NULL	NULL	NULL
17	14413	8877	NULL	NULL	0	19.06.2017 00:00:00	02.08.2017 00:00:00	NULL	NULL	NULL
18	14412	8877	0877	Austin, TX	0	03.08.2017 00:00:00	01.09.2017 00:00:00	NULL	NULL	NULL
19	14413	8877	NULL	NULL	1	02.09.2017 00:00:00	31.12.9999 00:00:00	NULL	NULL	NULL