@tonyjiang here is the actual working formulas:
//Data A
ClearCollect(
A,
{
No: 1,
Name: "Tom",
Product: "A1"
},
{
No: 1,
Name: "Tom",
Product: "A2"
},
{
No: 2,
Name: "Jack",
Product: "A1"
},
{
No: 3,
Name: "Jerry",
Product: "A1"
},
{
No: 3,
Name: "Jerry",
Product: "A3"
}
);
//Data B
ClearCollect(
B,
{
No: 1,
SubNo: 1,
Rate: "A"
},
{
No: 1,
SubNo: 2,
Rate: "A-"
},
{
No: 2,
SubNo: 1,
Rate: "A+"
},
{
No: 3,
SubNo: 1,
Rate: "A-"
},
{
No: 3,
SubNo: 2,
Rate: "B+"
}
)
And here is the formula to merge both base on No. column:
ClearCollect(
C,
AddColumns(
AddColumns(
A,
"MergeKey", No
),
"BData",
Filter(B, No = MergeKey)
)
)

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Thanks!