Inconsistent results in online/offline mode while join condition includes null

[lqy222]

table: t1
columns: [ "c1 string","c2 int","c3 bigint","c4 timestamp" ]
indexs: [ "index1:c1:c4" ]
rows:
- [ NULL,2,3,1590738989000 ]

table: t2
- columns: [ "c1 string","c2 int","c3 bigint","c4 timestamp" ]
 indexs: [ "index1:c1:c4" ]
rows:
 - [ NULL,2,3,1590738989000 ]

sql: select t1.c1,t1.c2,t2.c3,t2.c4 from t1 last join t2 ORDER BY t2.c4 on t1.c1=t2.c1;
expect rows:

• [ null,2,3,1590738989000 ]

real rows:

• [ null,2,null,null ]

[aceforeverd]

ref https://spark.apache.org/docs/3.0.0-preview/sql-ref-null-semantics.html#comp-operators

NULL = NULL outputs NULL, is not True.

[aceforeverd]

while the offline behavior is expected, related cases:

OpenMLDB/cases/function/join/test_lastjoin_simple.yaml

Lines 711 to 734 in 7a62b70

	- id: 19
	desc: 拼接条件中有null
	tags: [ "TODO", "@chenjing, @baoxinqi" ]
	inputs:
	- columns: [ "c1 string","c2 int","c3 bigint","c4 timestamp" ]
	indexs: [ "index1:c1:c4" ]
	rows:
	- [ NULL,2,3,1590738989000 ]
	- [ "bb",21,31,1590738990000 ]
	- columns: [ "c1 string","c2 int","c3 bigint","c4 timestamp" ]
	indexs: [ "index1:c1:c4" ]
	rows:
	- [ NULL,2,3,1590738989000 ]
	- [ "bb",22,31,1590738990000 ]
	- [ "ab",21,32,1590738993000 ]
	- [ "bb",22,31,1590738992000 ]
	- [ "bb",22,31,1590738991000 ]
	sql: select {0}.c1,{0}.c2,{1}.c3,{1}.c4 from {0} last join {1} ORDER BY {1}.c4 on {0}.c1={1}.c1;
	expect:
	columns: [ "c1 string","c2 int","c3 bigint","c4 timestamp" ]
	order: c1
	rows:
	- [ null,2,3,1590738989000 ]
	- [ "bb",21,31,1590738992000 ]

is turned off in online tests