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Queries have different plan with UNION

User505978 - OracleJun 5 2013 — edited Jun 6 2013
I have 2 query like this:

select * from emp where emp_no=2;

select * from emp where emp_no=3;

when i look at their execution plan seperately, it works fine and no problem but,

when i do this;

select * from emp where emp_no=2
union
select * from emp where emp_no=3;

i see different plan for both.

Is there a way to make use their own plan independently in union statement?

Comments

sb92075
What SET SPACE command?
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

15:21:39 SQL> help set space
SP2-0172: No HELP matching this topic was found.
15:21:43 SQL> help set

 SET
 ---

 Sets a system variable to alter the SQL*Plus environment settings
 for your current session. For example, to:
     -   set the display width for data
     -   customize HTML formatting
     -   enable or disable printing of column headings
     -   set the number of lines per page

 SET system_variable value

 where system_variable and value represent one of the following clauses:

   APPI[NFO]{OFF|ON|text}                   NEWP[AGE] {1|n|NONE}
   ARRAY[SIZE] {15|n}                       NULL text
   AUTO[COMMIT] {OFF|ON|IMM[EDIATE]|n}      NUMF[ORMAT] format
   AUTOP[RINT] {OFF|ON}                     NUM[WIDTH] {10|n}
   AUTORECOVERY {OFF|ON}                    PAGES[IZE] {14|n}
   AUTOT[RACE] {OFF|ON|TRACE[ONLY]}         PAU[SE] {OFF|ON|text}
     [EXP[LAIN]] [STAT[ISTICS]]             RECSEP {WR[APPED]|EA[CH]|OFF}
   BLO[CKTERMINATOR] {.|c|ON|OFF}           RECSEPCHAR {_|c}
   CMDS[EP] {;|c|OFF|ON}                    SERVEROUT[PUT] {ON|OFF}
   COLSEP {_|text}                            [SIZE {n | UNLIMITED}]
   CON[CAT] {.|c|ON|OFF}                      [FOR[MAT]  {WRA[PPED] |
   COPYC[OMMIT] {0|n}                          WOR[D_WRAPPED] |
   COPYTYPECHECK {ON|OFF}                      TRU[NCATED]}]
   DEF[INE] {&|c|ON|OFF}                    SHIFT[INOUT] {VIS[IBLE] |
   DESCRIBE [DEPTH {1|n|ALL}]                 INV[ISIBLE]}
     [LINENUM {OFF|ON}] [INDENT {OFF|ON}]   SHOW[MODE] {OFF|ON}
   ECHO {OFF|ON}                            SQLBL[ANKLINES] {OFF|ON}
   EDITF[ILE] file_name[.ext]               SQLC[ASE] {MIX[ED] |
   EMB[EDDED] {OFF|ON}                        LO[WER] | UP[PER]}
   ERRORL[OGGING] {ON|OFF}                  SQLCO[NTINUE] {> | text}
     [TABLE [schema.]tablename]             SQLN[UMBER] {ON|OFF}
     [TRUNCATE] [IDENTIFIER identifier]     SQLPLUSCOMPAT[IBILITY] {x.y[.z]}
   ESC[APE] {\|c|OFF|ON}                    SQLPRE[FIX] {#|c}
   ESCCHAR {@|?|%|$|OFF}                    SQLP[ROMPT] {SQL>|text}
   EXITC[OMMIT] {ON|OFF}                    SQLT[ERMINATOR] {;|c|ON|OFF}
   FEED[BACK] {6|n|ON|OFF}                  SUF[FIX] {SQL|text}
   FLAGGER {OFF|ENTRY|INTERMED[IATE]|FULL}  TAB {ON|OFF}
   FLU[SH] {ON|OFF}                         TERM[OUT] {ON|OFF}
   HEA[DING] {ON|OFF}                       TI[ME] {OFF|ON}
   HEADS[EP] {||c|ON|OFF}                   TIMI[NG] {OFF|ON}
   INSTANCE [instance_path|LOCAL]           TRIM[OUT] {ON|OFF}
   LIN[ESIZE] {80|n}                        TRIMS[POOL] {OFF|ON}
   LOBOF[FSET] {1|n}                        UND[ERLINE] {-|c|ON|OFF}
   LOGSOURCE [pathname]                     VER[IFY] {ON|OFF}
   LONG {80|n}                              WRA[P] {ON|OFF}
   LONGC[HUNKSIZE] {80|n}                   XQUERY {BASEURI text|
   MARK[UP] HTML [OFF|ON]                     ORDERING{UNORDERED|
     [HEAD text] [BODY text] [TABLE text]              ORDERED|DEFAULT}|
     [ENTMAP {ON|OFF}]                        NODE{BYVALUE|BYREFERENCE|
     [SPOOL {OFF|ON}]                              DEFAULT}|
     [PRE[FORMAT] {OFF|ON}]                   CONTEXT text}


15:21:48 SQL>
unknown-7404
>
What SET SPACE command?
>
Maybe he meant this obsolete one? 
SQL> select * from v$version;
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for Linux: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production
SQL>
SQL> set space 10
SQL>
SQL> set space 11
SP2-0267: space option 11 out of range (0 through 10)
SQL>
SQL*Plus User's Guide 11.1 - http://docs.oracle.com/cd/B28359_01/server.111/b31189.pdf
>
SET SPACE {1|n} (obsolete)
Sets the number of spaces between columns in output. The maximum value of n is 10.
The SET SPACE 0 and SET COLSEP " commands have the same effect. This command
is obsoleted by SET COLSEP, but you can still use it for backward compatibility. You
may prefer to use COLSEP because the SHOW command recognizes COLSEP and
does not recognize SPACE.
{quote}
unknown-7404
Use 'colsep' with a space 
SQL> set colsep ""
SQL> select 'A', 'B', 'C' FROM DUAL;
ABC
SQL> set colsep " "
SQL> select 'A', 'B', 'C' FROM DUAL;
A B C
SQL>
627703
the extra space goes away after I used alais.

SELECT 'A' as A, 'B' as B, 'C' as C
FROM TBL_XXX where rownum <3;

Thanks a lot for all your help!
Liz
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Locked on Jul 4 2013
Added on Jun 5 2013
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