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除非我存储值,否则序列不会递增

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4

在常规SQL中,每次调用 .NEXTVAL 时,我的序列都会递增:

SELECT PDF_DATOS_TITULO_ID_SEQ.CURRVAL FROM DUAL; -- 54
SELECT PDF_DATOS_TITULO_ID_SEQ.NEXTVAL FROM DUAL; -- 55
SELECT PDF_DATOS_TITULO_ID_SEQ.NEXTVAL FROM DUAL; -- 56
SELECT PDF_DATOS_TITULO_ID_SEQ.NEXTVAL FROM DUAL; -- 57
SELECT PDF_DATOS_TITULO_ID_SEQ.CURRVAL FROM DUAL; -- 57 (54+3, correct)

但是,在PL / SQL块内的动态SQL中,它不会增加:

SELECT PDF_DATOS_TITULO_ID_SEQ.CURRVAL FROM DUAL; -- 57
BEGIN
    EXECUTE IMMEDIATE 'SELECT PDF_DATOS_TITULO_ID_SEQ.NEXTVAL FROM DUAL';
    EXECUTE IMMEDIATE 'SELECT PDF_DATOS_TITULO_ID_SEQ.NEXTVAL FROM DUAL';
    EXECUTE IMMEDIATE 'SELECT PDF_DATOS_TITULO_ID_SEQ.NEXTVAL FROM DUAL';
END;
/
SELECT PDF_DATOS_TITULO_ID_SEQ.CURRVAL FROM DUAL; -- 57

...除非我将值存储到变量中:

SELECT PDF_DATOS_TITULO_ID_SEQ.CURRVAL FROM DUAL; -- 57 (!)
DECLARE
    FOO INTEGER;
BEGIN
    EXECUTE IMMEDIATE 'SELECT PDF_DATOS_TITULO_ID_SEQ.NEXTVAL FROM DUAL' INTO FOO;
    EXECUTE IMMEDIATE 'SELECT PDF_DATOS_TITULO_ID_SEQ.NEXTVAL FROM DUAL' INTO FOO;
    EXECUTE IMMEDIATE 'SELECT PDF_DATOS_TITULO_ID_SEQ.NEXTVAL FROM DUAL' INTO FOO;
END;
/
SELECT PDF_DATOS_TITULO_ID_SEQ.CURRVAL FROM DUAL; -- 60 (57+3, correct)

解释是什么?它是 EXECUTE IMMEDIATE 的记录行为吗?

在您提出要求之前,SQL需要是动态的,因为序列名称是可变的 .

1 回答

  • 9

    当你省略或批量返回子句时,Oracle只会解析sql但不会从中发出任何提取 . 在文档中没有明确说明会发生这种情况,但是文档确实指定当你有1行返回时你应该使用INTO,如果你有可能有多行返回,那么你应该使用INTO .

    例如 . :

    SQL> create sequence testseq;
    
    Sequence created.
    
    SQL> alter session set events '10046 trace name context forever';
    
    Session altered.
    
    SQL> exec execute immediate 'select testseq.nextval from dual';
    
    PL/SQL procedure successfully completed.
    
    SQL> alter session set events '10046 trace name context off';
    
    Session altered.
    
    SQL> exit
    

    我们在跟踪中看到Oracle没有对FETCH阶段感到困扰:

    =====================
    PARSING IN CURSOR #140341213531640 len=32 dep=1 uid=83 oct=3 lid=83 tim=1363260261727946 hv=956010684 ad='7ac66b58' sqlid='56jwk2hwgr45w'
    select testseq.nextval from dual
    END OF STMT
    PARSE #140341213531640:c=4001,e=50473,p=0,cr=2,cu=0,mis=1,r=0,dep=1,og=1,plh=112670795,tim=1363260261727944
    EXEC #140341213531640:c=0,e=219,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=1,plh=112670795,tim=1363260261728249
    STAT #140341213531640 id=1 cnt=0 pid=0 pos=1 obj=79530 op='SEQUENCE  TESTSEQ (cr=0 pr=0 pw=0 time=181 us)'
    STAT #140341213531640 id=2 cnt=0 pid=1 pos=1 obj=0 op='FAST DUAL  (cr=0 pr=0 pw=0 time=1 us cost=2 size=0 card=1)'
    CLOSE #140341213531640:c=4001,e=24391,dep=1,type=3,tim=1363260261752736
    EXEC #140341212444728:c=8002,e=75407,p=0,cr=2,cu=0,mis=0,r=1,dep=0,og=1,plh=0,tim=1363260261752783
    
    *** 2013-03-14 11:24:29.866
    CLOSE #140341212444728:c=0,e=37,dep=0,type=0,tim=1363260269866098
    =====================
    

    VS:

    SQL> alter session set events '10046 trace name context forever';
    
    Session altered.
    
    SQL> var a number
    SQL> exec execute immediate 'select testseq.nextval from dual' into :a;
    
    PL/SQL procedure successfully completed.
    
    SQL> alter session set events '10046 trace name context off';
    
    Session altered.
    

    现在:

    PARSING IN CURSOR #139830768042232 len=32 dep=1 uid=83 oct=3 lid=83 tim=1363260428931803 hv=956010684 ad='7ac66b58' sqlid='56jwk2hwgr45w'
    select testseq.nextval from dual
    END OF STMT
    PARSE #139830768042232:c=0,e=38,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=1,plh=112670795,tim=1363260428931802
    EXEC #139830768042232:c=0,e=86,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=1,plh=112670795,tim=1363260428931917
    FETCH #139830768042232:c=0,e=22,p=0,cr=0,cu=0,mis=0,r=1,dep=1,og=1,plh=112670795,tim=1363260428931980
    STAT #139830768042232 id=1 cnt=1 pid=0 pos=1 obj=79530 op='SEQUENCE  TESTSEQ (cr=0 pr=0 pw=0 time=39 us)'
    STAT #139830768042232 id=2 cnt=1 pid=1 pos=1 obj=0 op='FAST DUAL  (cr=0 pr=0 pw=0 time=2 us cost=2 size=0 card=1)'
    CLOSE #139830768042232:c=0,e=0,dep=1,type=3,tim=1363260428931980
    EXEC #139830768045912:c=0,e=294,p=0,cr=0,cu=0,mis=0,r=1,dep=0,og=1,plh=0,tim=1363260428931980
    
    *** 2013-03-14 11:27:13.138
    CLOSE #139830768045912:c=0,e=45,dep=0,type=0,tim=1363260433138490
    =====================
    

    可以看到FETCH . 我认为理想情况下,Oracle应该在用户发出没有定义INTO / BULK INTO的select的情况下抛出错误 .

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