impala/docs/topics/impala_delete.xml

<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="delete" rev="kudu">

  <title>DELETE Statement (<keyword keyref="impala28"/> or higher only)</title>
  <titlealts audience="PDF"><navtitle>DELETE</navtitle></titlealts>
  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="SQL"/>
      <data name="Category" value="Kudu"/>
      <data name="Category" value="Iceberg"/>
      <data name="Category" value="ETL"/>
      <data name="Category" value="Ingest"/>
      <data name="Category" value="DML"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Data Analysts"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      <indexterm audience="hidden">DELETE statement</indexterm>
      Deletes an arbitrary number of rows from a table.
      This statement only works for Kudu (from <keyword keyref="impala28"/>) and Iceberg tables (from <keyword keyref="impala43"/>).
    </p>

    <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock>
DELETE [FROM] [<varname>database_name</varname>.]<varname>table_name</varname> [ WHERE <varname>where_conditions</varname> ]

DELETE <varname>table_ref</varname> FROM [<varname>joined_table_refs</varname>] [ WHERE <varname>where_conditions</varname> ]
</codeblock>

    <p>
      The first form evaluates rows from one table against an optional
      <codeph>WHERE</codeph> clause, and deletes all the rows that
      match the <codeph>WHERE</codeph> conditions, or all rows if
      <codeph>WHERE</codeph> is omitted.
    </p>

    <p>
      The second form evaluates one or more join clauses, and deletes
      all matching rows from one of the tables. The join clauses can
      include tables of any kind, but the table from which the rows
      are deleted must be a Kudu or Iceberg table. The <codeph>FROM</codeph>
      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.
    </p>

    <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>

    <p>
      The conditions in the <codeph>WHERE</codeph> clause are the same ones allowed
      for the <codeph>SELECT</codeph> statement. See <xref href="impala_select.xml#select"/>
      for details.
    </p>

    <p>
      The conditions in the <codeph>WHERE</codeph> clause can refer to
      any combination of primary key columns or other columns. Referring to
      primary key columns in the <codeph>WHERE</codeph> clause is more efficient
      than referring to non-primary key columns (in case of Kudu tables).
    </p>

    <p>
      If the <codeph>WHERE</codeph> clause is omitted, all rows are removed from the table.
    </p>

    <p>
      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:
    </p>
    <ul>
      <li>
        <p>
          If some rows cannot be deleted because their
          some primary key columns are not found, due to their being deleted
          by a concurrent <codeph>DELETE</codeph> operation,
          the statement succeeds but returns a warning.
        </p>
      </li>
      <li>
        <p>
          A <codeph>DELETE</codeph> statement might also overlap with
          <codeph>INSERT</codeph>, <codeph>UPDATE</codeph>,
          or <codeph>UPSERT</codeph> statements 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 <codeph>DELETE</codeph> applies to rows that are
          inserted or updated while the <codeph>DELETE</codeph> is in progress.
        </p>
      </li>
    </ul>

    <p>
      Iceberg also allows concurrent DELETE operations, in which case the concurrent DELETEs might
      remove the same rows. This won't corrupt the table as Iceberg allows such behavior.
    </p>

    <p>
      The number of affected rows is reported in an <cmdname>impala-shell</cmdname> message
      and in the query profile.
    </p>

    <p conref="../shared/impala_common.xml#common/dml_blurb_kudu"/>

    <note conref="../shared/impala_common.xml#common/compute_stats_next"/>

    <p conref="../shared/impala_common.xml#common/example_blurb"/>

    <p>
      The following examples show how to delete rows from a specified
      table, either all rows or rows that match a <codeph>WHERE</codeph>
      clause:
    </p>

<codeblock>
-- Deletes all rows. The FROM keyword is optional.
DELETE FROM table;
DELETE 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 table WHERE c1 = 100;

-- Deletes all rows that match all the WHERE conditions.
DELETE FROM 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 table WHERE 1 = 0;
</codeblock>

    <p>
      The following examples show how to delete rows that are part
      of the result set from a join:
    </p>

<codeblock>
-- 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 table based on a join with another table.
DELETE t1 FROM table t1 JOIN other_table t2 ON t1.x = t2.x;

-- The tables can be joined in any order as long as the Kudu or Iceberg table
-- is specified as the deletion target.
DELETE t2 FROM non_kudu_non_ice_table t1 JOIN kudu_or_ice_table t2 ON t1.x = t2.x;
</codeblock>

    <p conref="../shared/impala_common.xml#common/related_info"/>

    <p>
      <xref href="impala_iceberg.xml#impala_iceberg"/>,
      <xref href="impala_kudu.xml#impala_kudu"/>, <xref href="impala_insert.xml#insert"/>,
      <xref href="impala_update.xml#update"/>, <xref href="impala_upsert.xml#upsert"/>
    </p>

  </conbody>

</concept>