[英]Counting number of '1' values in each bit position in Redshift column
我的Redshift表中有BIGINT列,並且我想要一個查詢,該查詢將:
例如(為了簡化示例,我已經將整數值寫為二進制):
column
--------
11011110 = 222
00000000 = 0
11111100 = 252
00011000 = 24
11111100 = 252
00011000 = 24
11000010 = 194
76543210 <- bit_position
將返回一個表,如:
bit_position count
0 0
1 2
2 3
3 5
4 5
5 2
6 4
7 4
在這種情況下,我將能夠獲得前五個bit_position:(3,4,6,7,2)
注意:一列最多可能有64個bit_positions。
您可以使用按位與&
檢查每個位置。
這是跨行的示例:
SELECT SUM(CASE WHEN bit_col & 64 > 0 THEN 1 ELSE 0 END) "1000000"
, SUM(CASE WHEN bit_col & 32 > 0 THEN 1 ELSE 0 END) "0100000"
, SUM(CASE WHEN bit_col & 16 > 0 THEN 1 ELSE 0 END) "0010000"
, SUM(CASE WHEN bit_col & 8 > 0 THEN 1 ELSE 0 END) "0001000"
, SUM(CASE WHEN bit_col & 4 > 0 THEN 1 ELSE 0 END) "0000100"
, SUM(CASE WHEN bit_col & 2 > 0 THEN 1 ELSE 0 END) "0000010"
, SUM(CASE WHEN bit_col & 1 > 0 THEN 1 ELSE 0 END) "0000001"
FROM my_table
;
1000000 | 0100000 | 0010000 | 0001000 | 0000100 | 0000010 | 0000001
---------+---------+---------+---------+---------+---------+---------
11 | 8 | 11 | 13 | 11 | 9 | 8
要將結果放在單個列中,您需要使用並集:
SELECT 1 AS "col", SUM(CASE WHEN bit_col & 64 > 0 THEN 1 ELSE 0 END) AS bit_count FROM my_table
UNION ALL SELECT 2 AS "col", SUM(CASE WHEN bit_col & 32 > 0 THEN 1 ELSE 0 END) AS bit_count FROM my_table
UNION ALL SELECT 3 AS "col", SUM(CASE WHEN bit_col & 16 > 0 THEN 1 ELSE 0 END) AS bit_count FROM my_table
UNION ALL SELECT 4 AS "col", SUM(CASE WHEN bit_col & 8 > 0 THEN 1 ELSE 0 END) AS bit_count FROM my_table
UNION ALL SELECT 5 AS "col", SUM(CASE WHEN bit_col & 4 > 0 THEN 1 ELSE 0 END) AS bit_count FROM my_table
UNION ALL SELECT 6 AS "col", SUM(CASE WHEN bit_col & 2 > 0 THEN 1 ELSE 0 END) AS bit_count FROM my_table
UNION ALL SELECT 7 AS "col", SUM(CASE WHEN bit_col & 1 > 0 THEN 1 ELSE 0 END) AS bit_count FROM my_table
ORDER BY bit_count DESC
;
position | bit_count
----------+-----------
6 | 6
7 | 6
4 | 4
5 | 4
2 | 0
3 | 0
1 | 0
http://docs.aws.amazon.com/redshift/latest/dg/r_OPERATOR_SYMBOLS.html
編輯:如果您想獲得更多動態效果,則需要使用UDF。 您可以從f_bitwise_to_string
UDF作為模板開始,然后從那里添加所需的內容。 https://github.com/awslabs/amazon-redshift-udfs/blob/master/scalar-udfs/f_bitwise_to_string.sql
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