SELECT ... LIMIT (trial implementation)
От | jwieck@debis.com (Jan Wieck) |
---|---|
Тема | SELECT ... LIMIT (trial implementation) |
Дата | |
Msg-id | m0zUBum-000EBQC@orion.SAPserv.Hamburg.dsh.de обсуждение исходный текст |
Ответы |
Re: [HACKERS] SELECT ... LIMIT (trial implementation)
Re: [HACKERS] SELECT ... LIMIT (trial implementation) Re: [HACKERS] SELECT ... LIMIT (trial implementation) Re: [HACKERS] SELECT ... LIMIT (trial implementation) |
Список | pgsql-hackers |
Here we go, this is up to now only for discussion, do not apply to CVS! Those involved into the LIMIT discussion please comment. Here is what I had in mind for the SELECT ... LIMIT. It adds SELECT ... [LIMIT count [, offset]] to the parser and arranges that these values are passed down to the executor. It is a clean implementation of LIMIT (regression tested) and the open items on it are to enable parameters and handle it in SQL functions and SPI stuff (currently ignored in both). Optimizing the executor would require the other sort node stuff discussion first to come to a conclusion. For now it skips final result rows - but that's already one step forward since it reduces the rows sent to the frontend to exactly that what LIMIT requested. I've seen the queryLimit by SET variable stuff and that really can break rewrite rules, triggers or functions. This is because the query limit will be inherited by any query (inserts, updates, deletes too) done by them. Have a rule for constraint deletes of referencing tuples CREATE RULE del_table1 AS ON DELETE TO table1 DO DELETE FROM table2 WHERE ref = OLD.key; If the user now sets the query limit to 1 via SET and deletes a row from table1, only the first found record in table2 will be constraint deleted, not all of them. This is a feature where users can get around rules that ensure data integrity. Jan -- #======================================================================# # It's easier to get forgiveness for being wrong than for being right. # # Let's break this rule - forgive me. # #======================================== jwieck@debis.com (Jan Wieck) # begin 644 opt_limit.diff.gz M'XL(`$]=)S8"`^4\:W?B1K*?R:_H82=98&1;$F^<>`^+F1DV&!S`N<DGCBP: M6SM"(I*PQSOQ?[]5_9!:(`$S<1Y[+V<&I.[JZJ[NZGIUM1?.<DE.[("$@7WJ M!\[=V:UE?Z#>XLSV5RO+6X3RX=1&F#W57U4JE6/0%-XAG;$3$:Q#`Z]6JG MVB)&N]WZZN3DY$`?J;9FI][HU&J\;27]88.IMC6H9J^(&E_K!)Y.OB+D;XYG MNYL%)<5-Y+CAV<K^&)W>%S-JUGX066YV7?@4VI9]3['VC5(;1H'CW?$V\.^L MPKI5/U!**H7"-4/>_TCM3>0'[ZFUOJ(K/W@B8;19+C.I,G1#,_1&0I>AFU#0 MDI05'"\J%`I+:D6;@)YCR0\;&CQ=TM"&/G^1SZR&]];SO8A^C(C-?\^!E@*4 MA8#'=5:VO_&B<TY)(9N4`M`26IX3/1&8#?M#F#URHZH91DL9N5'7C&HM'OGS MGD[>L$YZ`9!%B85##2/B^3#;R\!?D>B>DCOG@7J$#9<\6.Z&\D8YN,[P9T57 M(8U*WT@R-:)K)'3^0_UE29:5RVQ"Y.MI]+2FA<)W9#9G<Y2N9.-B$-^1P6A6 M&P\N,P!<ZD&]Z`?6JU;.`&(D`%CI$E9R51;+L`/FA-[&=0'N;7<X[6<`W#X! 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