What are the best way to find out in impala if table a is a subset of table b?
I have two parquet based external tables in Impala, like to know if one is the subset of another, what would be the best way to get that?
The two tables has same schema with dozen or even hundred fields
Thank you.
sql impala
asked Nov 15 '18 at 2:06
mdivkmdivk
68421126
add a comment |
I have two parquet based external tables in Impala, like to know if one is the subset of another, what would be the best way to get that?
The two tables has same schema with dozen or even hundred fields
Thank you.
sql impala
asked Nov 15 '18 at 2:06
mdivkmdivk
68421126
add a comment |
I have two parquet based external tables in Impala, like to know if one is the subset of another, what would be the best way to get that?
The two tables has same schema with dozen or even hundred fields
Thank you.
sql impala
asked Nov 15 '18 at 2:06
mdivkmdivk
68421126
I have two parquet based external tables in Impala, like to know if one is the subset of another, what would be the best way to get that?
The two tables has same schema with dozen or even hundred fields
Thank you.
sql impala
sql impala
asked Nov 15 '18 at 2:06
mdivkmdivk
68421126
asked Nov 15 '18 at 2:06
mdivkmdivk
68421126
asked Nov 15 '18 at 2:06
mdivkmdivk
68421126
asked Nov 15 '18 at 2:06
mdivkmdivk
68421126
asked Nov 15 '18 at 2:06
mdivkmdivk
68421126
68421126
add a comment |
add a comment |
1 Answer
1
active
oldest
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Assuming no duplicates in either table, then A would be a subset of B if the count from:
select count(*)
from B;
is the same as the count from:
select count(*)
from ((select * from a) union
(select * from b)
) ab;
That is, adding the rows of A to B and eliminating duplicates does not add any more rows.
This is not a strict subsetting relationship, because "A" could be equivalent to "B". For a strict subsetting relationship, add the condition that :
select count(*)
from A
is strictly less than the count of B.
This assumes that the types and columns in A and B are compatible -- a reasonable assumption if you are asking about one being a subset of the other.
answered Nov 15 '18 at 2:10
Gordon LinoffGordon Linoff
780k35310412
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Assuming no duplicates in either table, then A would be a subset of B if the count from:
select count(*)
from B;
is the same as the count from:
select count(*)
from ((select * from a) union
(select * from b)
) ab;
That is, adding the rows of A to B and eliminating duplicates does not add any more rows.
This is not a strict subsetting relationship, because "A" could be equivalent to "B". For a strict subsetting relationship, add the condition that :
select count(*)
from A
is strictly less than the count of B.
This assumes that the types and columns in A and B are compatible -- a reasonable assumption if you are asking about one being a subset of the other.
answered Nov 15 '18 at 2:10
Gordon LinoffGordon Linoff
780k35310412
add a comment |
Assuming no duplicates in either table, then A would be a subset of B if the count from:
select count(*)
from B;
is the same as the count from:
select count(*)
from ((select * from a) union
(select * from b)
) ab;
That is, adding the rows of A to B and eliminating duplicates does not add any more rows.
This is not a strict subsetting relationship, because "A" could be equivalent to "B". For a strict subsetting relationship, add the condition that :
select count(*)
from A
is strictly less than the count of B.
This assumes that the types and columns in A and B are compatible -- a reasonable assumption if you are asking about one being a subset of the other.
answered Nov 15 '18 at 2:10
Gordon LinoffGordon Linoff
780k35310412
add a comment |
Assuming no duplicates in either table, then A would be a subset of B if the count from:
select count(*)
from B;
is the same as the count from:
select count(*)
from ((select * from a) union
(select * from b)
) ab;
That is, adding the rows of A to B and eliminating duplicates does not add any more rows.
This is not a strict subsetting relationship, because "A" could be equivalent to "B". For a strict subsetting relationship, add the condition that :
select count(*)
from A
is strictly less than the count of B.
This assumes that the types and columns in A and B are compatible -- a reasonable assumption if you are asking about one being a subset of the other.
answered Nov 15 '18 at 2:10
Gordon LinoffGordon Linoff
780k35310412
Assuming no duplicates in either table, then A would be a subset of B if the count from:
select count(*)
from B;
is the same as the count from:
select count(*)
from ((select * from a) union
(select * from b)
) ab;
That is, adding the rows of A to B and eliminating duplicates does not add any more rows.
This is not a strict subsetting relationship, because "A" could be equivalent to "B". For a strict subsetting relationship, add the condition that :
select count(*)
from A
is strictly less than the count of B.
This assumes that the types and columns in A and B are compatible -- a reasonable assumption if you are asking about one being a subset of the other.
answered Nov 15 '18 at 2:10
Gordon LinoffGordon Linoff
780k35310412
edited Nov 15 '18 at 2:20
answered Nov 15 '18 at 2:10
Gordon LinoffGordon Linoff
780k35310412
answered Nov 15 '18 at 2:10
Gordon LinoffGordon Linoff
780k35310412
answered Nov 15 '18 at 2:10
Gordon LinoffGordon Linoff
780k35310412
780k35310412
add a comment |
add a comment |
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