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Updated on 2025-09-04 GMT+08:00

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Supported and Unsupported Scenarios

Scenarios Supported by Parallel Query

**Table 1** Scenarios supported by parallel query
Supported Scenario	Description
Scans	Full table scans, index scans, index range scans, index reverse scans, index point queries, and index pushdown
Queries	Single-table queries, multi-table joins, views, subqueries, and some CTE queries, non-partitioned table queries, single-partition queries of partitioned tables, and UNION/UNION ALL queries
Joins	BNL JOIN, BKA JOIN, HASH JOIN, NESTED LOOP JOIN, SEMI JOIN, ANTI JOIN, and OUTER JOIN
Subqueries	Conditional subqueries, scalar subqueries, some correlated subqueries, non-correlated subqueries, and derived tables
Data types	Integer, Character, Floating Point, and time
Expression calculation	Arithmetic expressions (+, -, *, %, /, \|, and &) and conditional expressions (<, <=, >, >=, <>, BETWEEN/AND, and IN)
Logical operations	OR, AND, and NOT
General functions	Character, Integer, and Time functions
Aggregate functions	COUNT, SUM, AVG, MIN, and MAX CAUTION: If you want a SQL statement containing the COUNT aggregate function to use parallel query, instead of InnoDB parallel query, set innodb_parallel_select_count to OFF.
Sorting, grouping, pagination, and filtering	ORDER BY, GROUP BY/DISTINCT, LIMIT/OFFSET, WHERE/HAVING, and column projection
EXPLAIN statements	EXPLAIN FORMAT=TREE, EXPLAIN ANALYZE (supported in 2.0.60.241200 and later), and EXPLAIN FORMAT=JSON introduced in MySQL 8.0 and traditional EXPLAIN statements

Scenarios Unsupported by Parallel Query

**Table 2** Scenarios unsupported by parallel query
Unsupported Scenario	Description
Statements	Non-query statements PREPARE statements System tables, temporary tables, and non-InnoDB tables Subqueries that cannot be converted to semi-joins Statements that do not meet the ONLY_FULL_GROUP_BY rules HASH JOIN operations, during which data overflows to disks Lock queries, such as SERIALIZABLE isolation level, FOR UPDATE or SHARE LOCK Recursive queries WITH ROLLUP Statements with keyword HIGH_PRIORITY No line of data returned in the execution result (The execution plan shows: Zero limit, Impossible WHERE, Impossible HAVING, No matching min/max row, Select tables optimized away, Impossible HAVING noticed after reading const tables, or no matching row in const table.) Columns with type ZEROFILL. Its column values can be optimized to constants. Stored procedures
Triggers	Triggers
Indexes	Spatial indexes Full-text indexes Index Merge
Functions	Window functions
	Spatial functions (such as SP_WITHIN_FUNC)
	User-defined functions
	REF functions (VIEW_REF, OUTER_REF, and AGGREGATE_REF)
	User-related functions (such as user, current_user, session_user, and system_user)
	Spatial relationship functions (such as MBRContains, MBRCoveredBy, MBRCovers, MBRDisjoint, MBREquals, MBRIntersects, MBROverlaps, MBRTouches, and MBRWithin)
	Functions starting with ST_
	Spatial functions (GIS): GeomCollection, GeometryCollection, LineString, MultiLineString, MultiPoint, MultiPolygon, Polygon, ST_Distance, and Point
	Encryption and hash functions: SHA, SHA1, SHA2, and MD5
	Lock and synchronization functions: get_lock, is_free_lock, is_used_lock, release_lock, release_all_locks, and sleep
	Other functions: extractvalue PS_CURRENT_THREAD_ID() and PS_THREAD_ID(CONNECTION_ID()) WAIT_FOR_EXECUTED_GTID_SET and WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS UNCOMPRESS(COMPRESS()) STATEMENT_DIGEST_TEXT BINARY and CONVERT Generated columns, BLOB, TEXT, JSON, and GEOMETRY GROUP_CONCAT JSON_ARRAYAGG/JSON_OBJECTAGG STD/STDDEV/STDDEV_POP VARIANCE/VAR_POP/VAR_SAMP BIT_AND, BIT_OR, and BIT_XOR set_user_var RAND functions with parameters json_* (such as json_length and json_type) st_distance xml_str weight_string row_count

Incompatibility Between Parallel Queries and Serial Queries

Number of errors or alarms
If an error or alarm message is displayed during serial queries, the error or alarm message will be displayed in each worker thread during the parallel queries. As a result, the total number of error or alarm messages increases.
Precision
During parallel queries, if there is a function type in a SELECT statement, additional stored procedures will be generated in the intermediate results. As a result, compared with serial queries, the precision of the floating point part in parallel queries may be different, and the final results may be slightly different.
Truncation
During the parallel queries, if there is a function type in a SELECT statement, additional stored procedures will be generated in the intermediate results. In this process, the calculation result of the function needs to be cached, and data truncation may occur (generally due to data type conversion, for example, covering a floating-point value to a character string). As a result, the final result is different from the serial queries.
Sequence of result sets
Because tasks are executed by multiple worker threads during parallel queries, the sequence of the returned result set may not be consistent with that of serial queries. In the case of a query with LIMIT, this problem is more likely to occur. If fields of GROUP BY are invisible characters, the sequence of the returned result set is also different.
UNION ALL result sets
UNION ALL ignores sort operators. The sequence of the returned result set in parallel execution may be different from that in non-parallel execution. In the case of a query with LIMIT, the result sets are different.