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- hashbucket(expression)
- DESCRIPTION:
Function returns the hash bucket number that corresponds to a specified row hash value.
If no row hash value is specified, functions returns the highest hash bucket number.
PARAMETERS:
expression:
Optional Argument.
Specifies a ColumnExpression of a column that evaluates to a valid BYTE(4)
row hash value.
Format for the argument: '<dataframe>.<dataframe_column>.expression'.
If expression does not appear in the argument list, then function returns an
INTEGER value that is the highest hash bucket number.
If expression evaluates to NULL, then function returns NULL.
If expression evaluates to a valid BYTE(4) row hash value, then function
returns the hash bucket number corresponding to the row hash value.
The range of values for hash bucket numbers depends on the system setting
of the hash bucket size.
* If the hash bucket size is 16 bits, the hash bucket numbers can have
a value from 0 to 65535.
* If the hash bucket size is 20 bits, the hash bucket numbers can have
a value from 0 to 1048575.
NOTE:
Function accepts positional arguments only.
EXAMPLES:
# Load the data to run the example.
>>> load_example_data("dataframe", "bytes_table")
>>>
# Create a DataFrame on 'bytes_table' table.
>>> bytes_table = DataFrame("bytes_table")
>>> bytes_table
byte_col varbyte_col blob_col
id_col
0 b'63' b'627A7863' b'3330363136323633'
2 b'61' b'616263643132' b'6162636431323233'
1 b'62' b'62717765' b'3331363136323633'
>>>
# Import func from sqlalchemy to execute hashbucket() function.
>>> from sqlalchemy import func
# Example 1: Return the maximum hash bucket values. To do so, execute function without any argument.
# Create a sqlalchemy Function object.
>>> hashbucket_func_ = func.hashbucket()
>>>
# Pass the Function object as input to DataFrame.assign().
>>> df = bytes_table.assign(hashbucket_max_=hashbucket_func_)
>>> print(df)
byte_col varbyte_col blob_col hashbucket_max_
id_col
0 b'63' b'627A7863' b'3330363136323633' 1048575
2 b'61' b'616263643132' b'6162636431323233' 1048575
1 b'62' b'62717765' b'3331363136323633' 1048575
>>>
# Example 2: Return the maximum hash bucket values corresponding to values in "byte_col" column.
# Create a sqlalchemy Function object.
# Function accepts column of type BYTE(4) only. Let's cast byte_col column to BYTE(4).
>>> from teradatasqlalchemy import BYTE
>>> hashbucket_func_ = func.hashbucket(bytes_table.byte_col.cast(BYTE(4)).expression)
>>>
# Pass the Function object as input to DataFrame.assign().
>>> df = bytes_table.assign(hashbucket_byte_col_=hashbucket_func_)
>>> print(df)
byte_col varbyte_col blob_col hashbucket_byte_col_
id_col
0 b'63' b'627A7863' b'3330363136323633' 405504
2 b'61' b'616263643132' b'6162636431323233' 397312
1 b'62' b'62717765' b'3331363136323633' 401408
>>>
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