From: drh <> Date: Thu, 16 Feb 2023 14:29:04 +0000 (+0000) Subject: Do not compute result columns of subqueries that are never used. Make those columns... X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=8b6f313f252b7b01fc7f57c1eb2c55cfc5b38613;p=thirdparty%2Fsqlite.git Do not compute result columns of subqueries that are never used. Make those columns NULL instead. This optimization potentially resolves the enhancement request described by [baa5bb76c35a124c|ticket baa5bb76c35a124c]. FossilOrigin-Name: 0163b697dd560b6ad78ae20b3ae495a051680b0faf1633827119db381869351f --- 8b6f313f252b7b01fc7f57c1eb2c55cfc5b38613 diff --cc manifest index fbe7326545,38e7b2731d..2badceaa7a --- a/manifest +++ b/manifest @@@ -1,5 -1,5 +1,5 @@@ - C Improve\sthe\sability\sof\sthe\squery\splanner\sto\srecognize\scovering\sindexes\seven\non\stables\swith\smore\sthan\s63\scolumns\sand\swhere\sthe\sindex\sis\sover\scolumns\nbeyond\sthe\s63rd\scolumn. - D 2022-10-24T13:50:04.830 -C Fix\sthe\ssubquery\sresult\scolumn\sNULL-ifier\sso\sthat\sit\scorrectly\shandles\nsubquery\scolumns\spast\sthe\s63rd\scolumn. -D 2023-02-15T19:53:08.659 ++C Do\snot\scompute\sresult\scolumns\sof\ssubqueries\sthat\sare\snever\sused.\sMake\sthose\scolumns\sNULL\sinstead.\sThis\soptimization\spotentially\sresolves\sthe\senhancement\srequest\sdescribed\sby\s[baa5bb76c35a124c|ticket\sbaa5bb76c35a124c]. ++D 2023-02-16T14:29:04.334 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1 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5612e9aecf934d6df7bba6ce861fdf5ba5456010 +F src/test8.c 3f7d0cc4e12e06832ba3db4455cb16867ccadafa602eb6ff5fcf097bffce56ed F src/test9.c 12e5ba554d2d1cbe0158f6ab3f7ffcd7a86ee4e5 F src/test_async.c 195ab49da082053fdb0f949c114b806a49ca770a F src/test_autoext.c 915d245e736652a219a907909bb6710f0d587871 @@@ -1820,9 -2045,8 +1820,8 @@@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a9 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0 - P 3da1032878bdc93f69b02926fb7243b31fe6b1a0ee93af68df52b203b0603dad - Q +f058773e41495ddbae698f9e9a4f62b7003112ea8614dfad69471340058735e4 - R f77ec747567c3bc99f563b3d82675b4b -P 5dec3cc0225296a043d17f73126d477d90a604f82b3180628176d8f950adbce8 -R d380059ff4fc01bc81597a53152668a1 ++P 3d1992de4733d4e155f2d6d5268323410d1104ab56db50f08a2bb26bf87d926b 77b220a7240425fa83e142ceef78505208e6e38d797070e146b9f7d255f753c7 ++R b3790c5c75be15bad2ca8d7c8cee6787 U drh - Z 75744969cee191ad91201d95cd6f1fac -Z d76a4bd1d7943a5eace66bda083496dd ++Z ce0e41ce709151b90d95961cc059402d # Remove this line to create a well-formed Fossil manifest. diff --cc manifest.uuid index 2dffe91d0b,149e343a10..a008c7610a --- a/manifest.uuid +++ b/manifest.uuid @@@ -1,1 -1,1 +1,1 @@@ - 3d1992de4733d4e155f2d6d5268323410d1104ab56db50f08a2bb26bf87d926b -77b220a7240425fa83e142ceef78505208e6e38d797070e146b9f7d255f753c7 ++0163b697dd560b6ad78ae20b3ae495a051680b0faf1633827119db381869351f diff --cc src/select.c index 0c8ecd1c9e,dc187dfa6a..8ea78d3d20 --- a/src/select.c +++ b/src/select.c @@@ -4375,6 -5235,57 +4375,57 @@@ static int pushDownWhereTerms } #endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */ + /* + ** Check to see if a subquery contains result-set columns that are + ** never used. If it does, change the value of those result-set columns + ** to NULL so that they do not cause unnecessary work to compute. + ** + ** Return the number of column that were changed to NULL. + */ -static int disableUnusedSubqueryResultColumns(SrcItem *pItem){ ++static int disableUnusedSubqueryResultColumns(struct SrcList_item *pItem){ + int nCol; + Select *pSub; /* The subquery to be simplified */ + Select *pX; /* For looping over compound elements of pSub */ + Table *pTab; /* The table that describes the subquery */ + int j; /* Column number */ + int nChng = 0; /* Number of columns converted to NULL */ + + assert( pItem!=0 ); + assert( pItem->pTab!=0 ); + pTab = pItem->pTab; + if( pTab->tabFlags & TF_Ephemeral ) return 0; + assert( pItem->pSelect!=0 ); + pSub = pItem->pSelect; + assert( pSub->pEList->nExpr==pTab->nCol ); + for(pX=pSub; pX; pX=pX->pPrior){ + if( pX->pPrior && pX->op!=TK_ALL ){ + /* This optimization does not work for compound subqueries that + ** use UNION, INTERSECT, or EXCEPT. Only UNION ALL is allowed. */ + return 0; + } + if( pX->pWin ){ + /* This optimization does not work for subqueries that use window + ** functions. */ + return 0; + } + } + nCol = pTab->nCol; + for(j=0; jcolUsed)!=0 ) continue; + for(pX=pSub; pX; pX=pX->pPrior) { + Expr *pY = pX->pEList->a[j].pExpr; + if( pY->op==TK_NULL ) continue; + pY->op = TK_NULL; - pX->selFlags |= SF_PushDown; ++ /* pX->selFlags |= SF_PushDown; */ + nChng++; + } + } + return nChng; + } + + /* ** The pFunc is the only aggregate function in the query. Check to see ** if the query is a candidate for the min/max optimization. @@@ -5870,10 -7379,25 +5921,24 @@@ int sqlite3Select sqlite3TreeViewSelect(0, p, 0); } #endif - assert( pItem->pSelect && (pItem->pSelect->selFlags & SF_PushDown)!=0 ); }else{ - TREETRACE(0x4000,pParse,p,("Push-down not possible\n")); + SELECTTRACE(0x100,pParse,p,("Push-down not possible\n")); } + /* Convert unused result columns of the subquery into simple NULL + ** expressions, to avoid unneeded searching and computation. + */ + if( disableUnusedSubqueryResultColumns(pItem) ){ + #if TREETRACE_ENABLED + if( sqlite3TreeTrace & 0x4000 ){ + TREETRACE(0x4000,pParse,p, + ("Change unused result columns to NULL for subquery %d:\n", + pSub->selId)); + sqlite3TreeViewSelect(0, p, 0); + } + #endif + } + zSavedAuthContext = pParse->zAuthContext; pParse->zAuthContext = pItem->zName;