Lars Volker 1ada9dac88 IMPALA-4166: Add SORT BY sql clause ...

This change adds support for adding SORT BY (...) clauses to CREATE
TABLE and ALTER TABLE statements. Examples are:

CREATE TABLE t (i INT, j INT, k INT) PARTITIONED BY (l INT) SORT BY (i, j);
CREATE TABLE t SORT BY (int_col,id) LIKE u;
CREATE TABLE t LIKE PARQUET '/foo' SORT BY (id,zip);

ALTER TABLE t SORT BY (int_col,id);
ALTER TABLE t SORT BY ();

Sort columns can only be specified for Hdfs tables and effectiveness may
vary based on storage type; for example TEXT tables will not see
improved compression. The SORT BY clause must not contain clustering
columns. The columns in the SORT BY clause are stored in the
'sort.columns' table property and will result in an additional SORT node
being added to the plan before the final table sink. Specifying sort
columns also enables clustering during inserts, so the SORT node will
contain all partitioning columns first, followed by the sort columns. We
do this because sort columns add a SORT node to the plan and adding the
clustering columns to the SORT node is cheap.

Sort columns supersede the sortby() hint, which we will remove in a
subsequent change (IMPALA-5144). Until then, it is possible to specify
sort columns using both ways at the same time and the column lists
will be concatenated.

Change-Id: I08834f38a941786ab45a4381c2732d929a934f75
Reviewed-on: http://gerrit.cloudera.org:8080/6495
Reviewed-by: Lars Volker <lv@cloudera.com>
Tested-by: Impala Public Jenkins

2017-05-12 15:43:30 +00:00

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