MySQL 8.0 Release Notes
MySQL 8.0 Source Code Documentation
These restrictions apply to the features described inChapter 25,Stored Objects.
Some of the restrictions noted here apply to all stored routines; that is, both to stored procedures and stored functions. There are also somerestrictions specific to stored functionsbut not to stored procedures.
The restrictions for stored functions also apply to triggers. There are also somerestrictions specific to triggers.
The restrictions for stored procedures also apply to theDOclause of Event Scheduler event definitions. There are also somerestrictions specific to events.
Stored routines cannot contain arbitrary SQL statements. The following statements are not permitted:
锁语句
LOCK TABLESandUNLOCK TABLES.SQL prepared statements (
PREPARE,EXECUTE,DEALLOCATE PREPARE) can be used in stored procedures, but not stored functions or triggers. Thus, stored functions and triggers cannot use dynamic SQL (where you construct statements as strings and then execute them).Generally, statements not permitted in SQL prepared statements are also not permitted in stored programs. For a list of statements supported as prepared statements, seeSection 13.5, “Prepared Statements”. Exceptions are
SIGNAL,RESIGNAL, andGET DIAGNOSTICS, which are not permissible as prepared statements but are permitted in stored programs.Because local variables are in scope only during stored program execution, references to them are not permitted in prepared statements created within a stored program. Prepared statement scope is the current session, not the stored program, so the statement could be executed after the program ends, at which point the variables would no longer be in scope. For example,
SELECT ... INTOcannot be used as a prepared statement. This restriction also applies to stored procedure and function parameters. SeeSection 13.5.1, “PREPARE Statement”.local_varWithin all stored programs (stored procedures and functions, triggers, and events), the parser treats
BEGIN [WORK]as the beginning of aBEGIN ... ENDblock. To begin a transaction in this context, useSTART TRANSACTIONinstead.
The following additional statements or operations are not permitted within stored functions. They are permitted within stored procedures, except stored procedures that are invoked from within a stored function or trigger. For example, if you useFLUSHin a stored procedure, that stored procedure cannot be called from a stored function or trigger.
Statements that perform explicit or implicit commit or rollback. Support for these statements is not required by the SQL standard, which states that each DBMS vendor may decide whether to permit them.
Statements that return a result set. This includes
SELECTstatements that do not have anINTOclause and other statements such asvar_listSHOW,EXPLAIN, andCHECK TABLE. A function can process a result set either withSELECT ... INTOor by using a cursor andvar_listFETCHstatements. SeeSection 13.2.10.1, “SELECT ... INTO Statement”, andSection 13.6.6, “Cursors”.FLUSHstatements.Stored functions cannot be used recursively.
存储函数or trigger cannot modify a table that is already being used (for reading or writing) by the statement that invoked the function or trigger.
If you refer to a temporary table multiple times in a stored function under different aliases, a
Can't reopen table: 'error occurs, even if the references occur in different statements within the function.tbl_name'HANDLER ... READstatements that invoke stored functions can cause replication errors and are disallowed.
For triggers, the following additional restrictions apply:
Triggers are not activated by foreign key actions.
使用基于行的复制时,触发器replica are not activated by statements originating on the source. The triggers on the replica are activated when using statement-based replication. For more information, seeSection 17.5.1.36, “Replication and Triggers”.
The
RETURNstatement is not permitted in triggers, which cannot return a value. To exit a trigger immediately, use theLEAVEstatement.Triggers are not permitted on tables in the
mysqldatabase. Nor are they permitted onINFORMATION_SCHEMAorperformance_schematables. Those tables are actually views and triggers are not permitted on views.The trigger cache does not detect when metadata of the underlying objects has changed. If a trigger uses a table and the table has changed since the trigger was loaded into the cache, the trigger operates using the outdated metadata.
The same identifier might be used for a routine parameter, a local variable, and a table column. Also, the same local variable name can be used in nested blocks. For example:
CREATE PROCEDURE p (i INT) BEGIN DECLARE i INT DEFAULT 0; SELECT i FROM t; BEGIN DECLARE i INT DEFAULT 1; SELECT i FROM t; END; END;In such cases, the identifier is ambiguous and the following precedence rules apply:
A local variable takes precedence over a routine parameter or table column.
A routine parameter takes precedence over a table column.
A local variable in an inner block takes precedence over a local variable in an outer block.
The behavior that variables take precedence over table columns is nonstandard.
Use of stored routines can cause replication problems. This issue is discussed further inSection 25.7, “Stored Program Binary Logging”.
The--replicate-wild-do-table=选择适用于选项卡les, views, and triggers. It does not apply to stored procedures and functions, or events. To filter statements operating on the latter objects, use one or more of thedb_name.tbl_name--replicate-*-dboptions.
The MySQL stored routine syntax is based on the SQL:2003 standard. The following items from that standard are not currently supported:
UNDOhandlersFORloops
To prevent problems of interaction between sessions, when a client issues a statement, the server uses a snapshot of routines and triggers available for execution of the statement. That is, the server calculates a list of procedures, functions, and triggers that may be used during execution of the statement, loads them, and then proceeds to execute the statement. While the statement executes, it does not see changes to routines performed by other sessions.
For maximum concurrency, stored functions should minimize their side-effects; in particular, updating a table within a stored function can reduce concurrent operations on that table. A stored function acquires table locks before executing, to avoid inconsistency in the binary log due to mismatch of the order in which statements execute and when they appear in the log. When statement-based binary logging is used, statements that invoke a function are recorded rather than the statements executed within the function. Consequently, stored functions that update the same underlying tables do not execute in parallel. In contrast, stored procedures do not acquire table-level locks. All statements executed within stored procedures are written to the binary log, even for statement-based binary logging. SeeSection 25.7, “Stored Program Binary Logging”.
The following limitations are specific to the Event Scheduler:
Event names are handled in case-insensitive fashion. For example, you cannot have two events in the same database with the names
anEventandAnEvent.An event may not be created, altered, or dropped from within a stored program, if the event name is specified by means of a variable. An event also may not create, alter, or drop stored routines or triggers.
DDL statements on events are prohibited while a
LOCK TABLESstatement is in effect.Event timings using the intervals
YEAR,QUARTER,月, andYEAR_MONTHare resolved in months; those using any other interval are resolved in seconds. There is no way to cause events scheduled to occur at the same second to execute in a given order. In addition—due to rounding, the nature of threaded applications, and the fact that a nonzero length of time is required to create events and to signal their execution—events may be delayed by as much as 1 or 2 seconds. However, the time shown in theINFORMATION_SCHEMA.EVENTStable'sLAST_EXECUTEDcolumn is always accurate to within one second of the actual event execution time. (See also Bug #16522.)Each execution of the statements contained in the body of an event takes place in a new connection; thus, these statements have no effect in a given user session on the server's statement counts such as
Com_selectandCom_insertthat are displayed bySHOW STATUS. However, such countsareupdated in the global scope. (Bug #16422)Events do not support times later than the end of the Unix Epoch; this is approximately the beginning of the year 2038. Such dates are specifically not permitted by the Event Scheduler. (Bug #16396)
References to stored functions, loadable functions, and tables in the
ON SCHEDULEclauses ofCREATE EVENTand改变事件statements are not supported. These sorts of references are not permitted. (See Bug #22830 for more information.)
While stored procedures, stored functions, triggers, and scheduled events are all supported by tables using theNDBstorage engine, you must keep in mind that these donotpropagate automatically between MySQL Servers acting as Cluster SQL nodes. This is because stored routine and trigger definitions are stored in tables in themysqlsystem database usingInnoDBtables, which are not copied between Cluster nodes.
Any stored routine or trigger that interacts with MySQL Cluster tables must be re-created by running the appropriateCREATE PROCEDURE,CREATE FUNCTION, orCREATE TRIGGERstatements on each MySQL Server that participates in the cluster where you wish to use the stored routine or trigger. Similarly, any changes to existing stored routines or triggers must be carried out explicitly on all Cluster SQL nodes, using the appropriateALTERorDROPstatements on each MySQL Server accessing the cluster.
Warning
Donotattempt to work around the issue just described by converting anymysqldatabase tables to use theNDBstorage engine.Altering the system tables in themysqldatabase is not supportedand is very likely to produce undesirable results.