Calculating differences between two rows for access sql query -

i trying create query new column containing differences between row n , row n+1 column x table 1.

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table 1

sample_id: 1, 2, 3, 4, 5

x: 42060, 42069, 42069, 42111, 42132

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query 1 (ideal result)

sample_id: 1, 2, 3, 4, 5

diff: 0, 9, 0, 42, 21

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i used following sql.

select [table1].sample_id,[table1].x - prev.x diff [table1] inner join [table1] prev on [table1].sample_id -1 = prev.sample_id [table1].sample_id > 1 

however, omits first row; thus, instead of getting result presented above query 1, following.

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results

sample_id: 2, 3, 4, 5

diff: 9, 0, 42, 21

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how can retain first row (sample_id=1) 0 value?

try this

select [table1].sample_id,[table1].x - prev.x diff   [table1]         inner join [table1] prev on [table1].sample_id -1 = prev.sample_id  [table1].sample_id >= 1 

which pick rows have sampleid greater or equal 1, or

select [table1].sample_id,[table1].x - prev.x diff   [table1]         inner join [table1] prev on [table1].sample_id -1 = prev.sample_id  [table1].sample_id not null 

which pick rows have sampleid