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MySQL Of function There are various restrictions on creation , The limitations of frequently used statements are as follows :

1、CONTAINS_DYNAMIC_SQL

CREATE function f1() returns int 
BEGIN
  set @cmd = 'select * from t1';
  PREPARE stmt1 FROM @cmd;
  EXECUTE IMMEDIATE @cmd;
  return 1;
END;

SQL Error [1336] [0A000]: Dynamic SQL is not allowed in stored function or trigger

If in function Include when creating PREPARE,EXECUTE, DEALLOCATE, Then these will be judged to include DYNAMIC SQL, These grammars will be rejected . Because the purpose of using stored procedures is to prevent the use of strictly typed data SQL Inject . In this case sql The statement is fixed , It's gone prepare The meaning of using , So there is no need to create such a scenario ..

2、MULTI_RESULTS

CREATE function f1() returns int 
BEGIN
  select * from tb_tmp;
  return 1;
END;

SQL Error [1415] [0A000]: Not allowed to return a result set from a function

here select Statement will return multiple lines of results , and function Only one fixed result can be returned , Therefore, this situation is not allowed .

3、HAS_COMMIT_OR_ROLLBACK

CREATE function f1() returns int 
BEGIN
  commit;
  return 1;
END;

SQL Error [1422] [HY000]: Explicit or implicit commit is not allowed in stored function or trigger.

Because in procedure Of set x=fi() In the scene of , One set The statement contains begin work and commit work, If f1 Yes commit It will affect the management behind the transaction .

4、 Other situations

In addition to the above, there are other 2 Species will also be rejected ： Namely HAS_SQLCOM_RESET、HAS_SQLCOM_FLUSH. Avoid when using .

5、 Additional explanation

stay procedure One of them contains begin and commit In addition to the above mentioned set, also IF, CASE, DECLARE, RETURN, These commands will be set when they are created open_tables=true, And then execute open_and_lock_tables, When the sub command is executed, proceed to rollback perhaps commit operation .

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GreatSQL It is maintained by Wanli database MySQL Branch , Focus on Improvement MGR Reliability and performance , Support InnoDB Parallel query feature , It is suitable for financial grade applications MySQL Branch version .

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