DELETE Statement (Impala 2.8 or higher only)
Deletes an arbitrary number of rows from a Kudu table. This statement only works for Impala tables that use the Kudu storage engine.
DELETE [FROM] [database_name.]table_name [ WHERE where_conditions ] DELETE table_ref FROM [joined_table_refs] [ WHERE where_conditions ]
The first form evaluates rows from one table against an optional
WHERE clause, and deletes all the rows that
WHERE conditions, or all rows if
WHERE is omitted.
The second form evaluates one or more join clauses, and deletes
all matching rows from one of the tables. The join clauses can
include non-Kudu tables, but the table from which the rows
are deleted must be a Kudu table. The
keyword is required in this case, to separate the name of
the table whose rows are being deleted from the table names
of the join clauses.
The conditions in the
WHERE clause are the same ones allowed
SELECT statement. See SELECT Statement
The conditions in the
WHERE clause can refer to
any combination of primary key columns or other columns. Referring to
primary key columns in the
WHERE clause is more efficient
than referring to non-primary key columns.
WHERE clause is omitted, all rows are removed from the table.
Because Kudu currently does not enforce strong consistency during concurrent DML operations, be aware that the results after this statement finishes might be different than you intuitively expect:
If some rows cannot be deleted because their some primary key columns are not found, due to their being deleted by a concurrent
DELETEoperation, the statement succeeds but returns a warning.
DELETEstatement might also overlap with
UPSERTstatements running concurrently on the same table. After the statement finishes, there might be more or fewer rows than expected in the table because it is undefined whether the
DELETEapplies to rows that are inserted or updated while the
DELETEis in progress.
The number of affected rows is reported in an impala-shell message and in the query profile.
Statement type: DML
COMPUTE STATSstatement to make sure all statistics are up-to-date. Consider updating statistics for a table after any
LOAD DATA, or
CREATE TABLE AS SELECTstatement in Impala, or after loading data through Hive and doing a
REFRESH table_namein Impala. This technique is especially important for tables that are very large, used in join queries, or both.
The following examples show how to delete rows from a specified
table, either all rows or rows that match a
-- Deletes all rows. The FROM keyword is optional. DELETE FROM kudu_table; DELETE kudu_table; -- Deletes 0, 1, or more rows. -- (If c1 is a single-column primary key, the statement could only -- delete 0 or 1 rows.) DELETE FROM kudu_table WHERE c1 = 100; -- Deletes all rows that match all the WHERE conditions. DELETE FROM kudu_table WHERE (c1 > c2 OR c3 IN ('hello','world')) AND c4 IS NOT NULL; DELETE FROM t1 WHERE (c1 IN (1,2,3) AND c2 > c3) OR c4 IS NOT NULL; DELETE FROM time_series WHERE year = 2016 AND month IN (11,12) AND day > 15; -- WHERE condition with a subquery. DELETE FROM t1 WHERE c5 IN (SELECT DISTINCT other_col FROM other_table); -- Does not delete any rows, because the WHERE condition is always false. DELETE FROM kudu_table WHERE 1 = 0;
The following examples show how to delete rows that are part of the result set from a join:
-- Remove _all_ rows from t1 that have a matching X value in t2. DELETE t1 FROM t1 JOIN t2 ON t1.x = t2.x; -- Remove _some_ rows from t1 that have a matching X value in t2. DELETE t1 FROM t1 JOIN t2 ON t1.x = t2.x WHERE t1.y = FALSE and t2.z > 100; -- Delete from a Kudu table based on a join with a non-Kudu table. DELETE t1 FROM kudu_table t1 JOIN non_kudu_table t2 ON t1.x = t2.x; -- The tables can be joined in any order as long as the Kudu table -- is specified as the deletion target. DELETE t2 FROM non_kudu_table t1 JOIN kudu_table t2 ON t1.x = t2.x;