Recursive SQL Mapping#
recursiveSql mapping allows executing recursive SQL transformation which contains Spark SQL code.
mappings: factorial: kind: recursiveSql sql: " SELECT 0 AS n, 1 AS fact UNION ALL SELECT n+1 AS n, (n+1)*fact AS fact FROM __this__ WHERE n < 6 "
Within the first step,
__this__ is assigned an empty table. Then the SQL query is executed for the first time,
which will provide the next value of the forthcoming iterations. In each iteration, the result of the previous
iteration is assigned to
__this__ and the query is executed again. Then the result is compared to the result of
the previous iteration. If the results are the same, a fix point is reached and the
execution stops. Otherwise, the iteration will continue.
kind(mandatory) (type: string):
broadcast(optional) (type: boolean) (default: false): Hint for broadcasting the result of this mapping for map-side joins.
cache(optional) (type: string) (default: NONE): Cache mode for the results of this mapping. Supported values are
NONE- Disables caching of teh results of this mapping
DISK_ONLY- Caches the results on disk
MEMORY_ONLY- Caches the results in memory. If not enough memory is available, records will be uncached.
MEMORY_ONLY_SER- Caches the results in memory in a serialized format. If not enough memory is available, records will be uncached.
MEMORY_AND_DISK- Caches the results first in memory and then spills to disk.
MEMORY_AND_DISK_SER- Caches the results first in memory in a serialized format and then spills to disk.
sql(optional) (type: string) (default: empty): The SQL statement to execute
file(optional) (type: string) (default: empty): The name of a file containing the SQL to execute.
uri(optional) (type: string) (default: empty): A URL pointing to a resource containing the SQL to execute.
maxIterations(optional) (type: int) (default: 99): The maximum of iterations. The mapping will fail if the number of actual iterations required to find the fix point exceeds this number.
main- the only output of the mapping
recursiveSql mapping allows executing recursive SQL statements, which refer to themselves. The result of each
step is made available as a temporary table
__this__. Currently, the query has to be a
UNION where the first part
may not contain a reference to
__this__. The first part of the
UNION will be used to determine the schema of the
Flowman also supports
iterativeSql mappings, which provide similar functionality.