Add DELETE ... RETURNING clause support - #725
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Implement the RETURNING clause for single-table DELETE statements, allowing the statement to return a result set of the deleted rows. Syntax: DELETE FROM t WHERE ... RETURNING select_expr [, ...] Supported features: - Any SQL expression computable from row fields (columns, functions, arithmetic, subqueries) - Aliases via AS keyword - Wildcard expansion (*, table.*) - Table-qualified column references - Correlated scalar subqueries in RETURNING - IN/EXISTS subqueries in RETURNING - User-defined functions in RETURNING - Works with WHERE, ORDER BY, LIMIT, PARTITION clauses - Works with updatable views - Works with prepared statements - Works with stored procedures (CALL with multi-result protocol) - Works with BEFORE/AFTER DELETE triggers - Respects EXPLAIN (no side effects) - Compatible with ONLY_FULL_GROUP_BY sql_mode Restrictions: - Not allowed in multi-table DELETE (syntax error at parser level) - Aggregate functions not allowed (ER_INVALID_GROUP_FUNC_USE) - RETURNING can no longer be used unquoted as an identifier; it must be backtick-quoted. See the sql_yacc.yy comment for the rationale. Implementation: - Parser (sql_yacc.yy): Add opt_delete_returning rule to single-table delete_stmt. Remove RETURNING_SYM from ident_keywords_unambiguous to avoid a reduce/reduce conflict with the select_alias grammar. - Parse tree (parse_tree_nodes.h/.cc): Add opt_returning_list member to PT_delete. Set parsing_place=CTX_SELECT_LIST during contextualization so subqueries get proper outer_context for outer reference resolution. - Command (sql_delete.h): Add m_returning flag to Sql_cmd_delete. - Preparation (sql_delete.cc): In prepare_inner(), expand wildcards via setup_wild(), resolve RETURNING items via setup_fields(SELECT_ACL), validate no aggregates, set up Query_result_send. Skip multi-table conversion (hypergraph and subquery paths) when RETURNING is present. Pass empty field list to setup_order() to avoid crash from unresolved RETURNING items in base_ref_items. - Execution (sql_delete.cc): In delete_from_single_table(), skip delete_all_rows() optimization, send result set metadata before loop, evaluate and send RETURNING row data before each delete, send EOF instead of my_ok(). Handle empty result sets on all early-exit paths including execute_inner() is_empty_query() path. - Stored procedures (sp.cc): Flag DELETE ... RETURNING with sp_head::MULTI_RESULTS so CALL sets SERVER_MORE_RESULTS_EXISTS, enabling the client multi-result protocol. - Access (sql_lex.h): Make setup_wild() public for use by Sql_cmd_delete. Tests: mysql-test/t/delete_returning.test (26 test cases covering basic expressions, errors, subqueries, ORDER BY+LIMIT, views, prepared statements, stored procedures, triggers, EXPLAIN, partitions, sql_mode, and privilege checks) Also update mysql-test/suite/json/t/json_value.test to backtick-quote the RETURNING identifier, which is required by the keyword change above. This contribution is under the OCA signed by Amazon and covering submissions to the MySQL project.
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This contribution is under the OCA signed by Amazon and covering submissions to the MySQL project.
What does this change do?
Adds support for a RETURNING clause on single-table DELETE statements, so a DELETE can return a result set built from the rows it deleted instead of just an affected-row count. The clause goes after ORDER BY/LIMIT and accepts the same expression list as a SELECT output list, including *, qualified wildcards, aliases, and subqueries:
DELETE FROM products
WHERE obsolete = 1
ORDER BY created_at
LIMIT 100
RETURNING id, name, created_at;
The rows are sent to the client as an ordinary result set, protocol-identical to a SELECT.
Why is it needed?
Returning data from modified rows is a well-established SQL pattern: PostgreSQL has supported it since 8.2, MariaDB since 10.0 for DELETE, and it appears in the SQL:2016 standard draft. It removes the need to run a SELECT before the DELETE to capture the doomed rows, which matters in three ways:
*) Audit logging and archival can capture computed or generated column values of deleted rows in one statement rather than a SELECT + DELETE round trip.
*) Queue-table and work-claiming patterns become a single atomic statement, which is the common way to hand rows to a downstream pipeline.
*) It removes a class of application-level race conditions. The SELECT-then-DELETE pattern needs explicit locking or serializable isolation to be correct under concurrency; DELETE ... RETURNING doesn't, because the read and the delete are the same operation.
How was it tested?
Added/updated MTR tests under
mysql-test/t/delete_returning.testscripts/ci/mtr.shpasses locallyRan the relevant full suite (name it): main,innodb
Contributor checklist
I have signed the OCA with the email on these commits
Code is formatted (
scripts/ci/format.sh)Commits are focused with descriptive messages
AI assistance
I did not use AI assistance for this contribution
I used AI assistance for this contribution
If AI assistance was used, describe the tool(s) and extent of use:
Anthropic Opus was used as coding assistant, in test generation and review.
Whole submitted code and tests were manually reviewed and manually tested.
Areas touched
Parser, DELETE query executor.
Side-effects
The change removes RETURNING_SYM from ident_keywords_unambiguous, so unquoted RETURNING can no longer be used as an identifier and must be backtick-quoted. The reasoning is in the sql_yacc.yy comment.