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If terms of the WHERE clause require that the right table in a LEFT JOIN

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not be a null row, then simplify the LEFT JOIN into an ordinary JOIN.

FossilOrigin-Name: 5b7abecc7ab8ccbbb8cb5e0f672e67625c2555ad03442efbf34cb395f5bb71a8
This commit is contained in:
drh
2018-03-20 21:16:15 +00:00
parent f6e6f02308
commit 2589787c5a
7 changed files with 109 additions and 14 deletions
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23
manifest
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@ -1,5 +1,5 @@
C Fix\sincorrect\stestcase\slabels\son\stwo\scases\sin\sjoin5.test.\s\sNo\schanges\sto\scode.
D 2018-03-20T19:02:03.726
C If\sterms\sof\sthe\sWHERE\sclause\srequire\sthat\sthe\sright\stable\sin\sa\sLEFT\sJOIN\nnot\sbe\sa\snull\srow,\sthen\ssimplify\sthe\sLEFT\sJOIN\sinto\san\sordinary\sJOIN.
D 2018-03-20T21:16:15.180
F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
F Makefile.in 7016fc56c6b9bfe5daac4f34be8be38d8c0b5fab79ccbfb764d3b23bf1c6fff3
@ -441,7 +441,7 @@ F src/date.c ebe1dc7c8a347117bb02570f1a931c62dd78f4a2b1b516f4837d45b7d6426957
F src/dbpage.c 8db4c97f630e7d83f884ea75caf1ffd0988c160e9d530194d93721c80821e0f6
F src/dbstat.c 7a4ba8518b6369ef3600c49cf9c918ad979acba610b2aebef1b656d649b96720
F src/delete.c 20c8788451dc737a967c87ea53ad43544d617f5b57d32ccce8bd52a0daf9e89b
F src/expr.c 904f85e5f5fa232488cbb662fcf3306ae203728751468670fb9840a9b1886abc
F src/expr.c 21ba8e1f8b9bc035053941d4f8df3ca5376be5e63ff62f945c2bc4f9b8890362
F src/fault.c 460f3e55994363812d9d60844b2a6de88826e007
F src/fkey.c d617daf66b5515e2b42c1405b2b4984c30ca50fb705ab164271a9bf66c69e331
F src/func.c 94f42cba2cc1c34aeaa441022ba0170ec3fec4bba54db4e0ded085c6dc0fdc51
@ -489,12 +489,12 @@ F src/printf.c d3b7844ddeb11fbbdd38dd84d09c9c1ac171d21fb038473c3aa97981201cc660
F src/random.c 80f5d666f23feb3e6665a6ce04c7197212a88384
F src/resolve.c 66c73fcb7719b8ff0e841b58338f13604ff3e2b50a723f9b8f383595735262f6
F src/rowset.c 7b7e7e479212e65b723bf40128c7b36dc5afdfac
F src/select.c 69ed6ca9d1bf4adb41472b0740b7b90868438dedcdd5ab2fd608070eca30d073
F src/select.c 965e1791b10d9384bc9d42bc8109ba5863dfa094e3584b3f0643970aa507ccfc
F src/shell.c.in 911b9e3bce40413c78fdba28efa28363e98183819bd4b300780bf57bacfc4b84
F src/sqlite.h.in 19762b57baa1ade67531f254de94374428fb9c82452ef305017847945f9c2911
F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
F src/sqlite3ext.h 83a3c4ce93d650bedfd1aa558cb85a516bd6d094445ee989740827d0d944368d
F src/sqliteInt.h 7e9deb145c110289f50fcf72a8742d030834885676482391fe83c3cee75f97d4
F src/sqliteInt.h 541896393a2ac07de571bcb0ce05b9422b94a6fb3900b005fa095d70b4d9545a
F src/sqliteLimit.h 1513bfb7b20378aa0041e7022d04acb73525de35b80b252f1b83fedb4de6a76b
F src/status.c 46e7aec11f79dad50965a5ca5fa9de009f7d6bde08be2156f1538a0a296d4d0e
F src/table.c b46ad567748f24a326d9de40e5b9659f96ffff34
@ -771,7 +771,7 @@ F test/e_fts3.test 8cf40550bb088a6aa187c818c00fabe26ef82900a4cd5c66b427ccafe28be
F test/e_insert.test f02f7f17852b2163732c6611d193f84fc67bc641fb4882c77a464076e5eba80e
F test/e_reindex.test 2bebf7b393e519198b7c654407221cf171a439b8
F test/e_resolve.test a61751c368b109db73df0f20fc75fb47e166b1d8
F test/e_select.test 16651bb681e83a1a2875ff4a595ed2b4b4dee375
F test/e_select.test 6fd45fd4a59ec82b6dda7468699dcc0ec1a72538577750b4f90357a62c1d2723
F test/e_select2.test aceb80ab927d46fba5ce7586ebabf23e2bb0604f
F test/e_totalchanges.test b12ee5809d3e63aeb83238dd501a7bca7fd72c10
F test/e_update.test f46c2554d915c9197548681e8d8c33a267e84528
@ -1004,7 +1004,7 @@ F test/ioerr5.test 2edfa4fb0f896f733071303b42224df8bedd9da4
F test/ioerr6.test a395a6ab144b26a9e3e21059a1ab6a7149cca65b
F test/istrue.test 2d89873d72248b7a0ef7b5457120100cce75a19181bcf4b30e90a3f96a5c5558
F test/join.test 442c462eea85cf065d70a663c626b780a95af6e11585d909bb63b87598afe678
F test/join2.test f1b5ba94ba70a791df2d99e61adcebf62edacad1eca57881c97eb3e2ca718595
F test/join2.test 2339e3a8089178607a718c7fa1f6c3826579132396f5304a0f8e9dbefa60c84f
F test/join3.test 6f0c774ff1ba0489e6c88a3e77b9d3528fb4fda0
F test/join4.test 1a352e4e267114444c29266ce79e941af5885916
F test/join5.test c6bd62effc37a152bea735f9ef241b19bb967bd4593dc99b20e2fc55ae707e38
@ -1712,7 +1712,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
P 5ad668d4339397fe66fe085e0527e37a1930917da88d462a8d89a465faa15e28
R de2d87ae55e8927dcebc8ba7daa8abff
P 4661ac81c9589b06a07df8b7931fbd0a7f9a4e9ba1448192b70701dc85a29bd2
R 1fe493b73142e6f35ada0785e4320aab
T *branch * join-strength-reduction
T *sym-join-strength-reduction *
T -sym-trunk *
U drh
Z 13d930ad372c9908126067c6c04be90c
Z 28874e198dec3af552f1abf3ec72242e

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manifest.uuid
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@ -1 +1 @@
4661ac81c9589b06a07df8b7931fbd0a7f9a4e9ba1448192b70701dc85a29bd2
5b7abecc7ab8ccbbb8cb5e0f672e67625c2555ad03442efbf34cb395f5bb71a8

52
src/expr.c
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@ -5001,6 +5001,58 @@ int sqlite3ExprImpliesExpr(Parse *pParse, Expr *pE1, Expr *pE2, int iTab){
return 0;
}
/*
** This is the Expr node callback for sqlite3ExprImpliesNotNullRow().
** If the expression node requires that the table at pWalker->iCur
** have a non-NULL column, then set pWalker->eCode to 1 and abort.
*/
static int impliesNotNullRow(Walker *pWalker, Expr *pExpr){
if( ExprHasProperty(pExpr, EP_FromJoin) ) return WRC_Prune;
switch( pExpr->op ){
case TK_ISNULL:
case TK_IS:
case TK_OR:
case TK_FUNCTION:
case TK_AGG_FUNCTION:
return WRC_Prune;
case TK_COLUMN:
case TK_AGG_COLUMN:
if( pWalker->u.iCur==pExpr->iTable ){
pWalker->eCode = 1;
return WRC_Abort;
}
return WRC_Prune;
default:
return WRC_Continue;
}
}
/*
** Return true (non-zero) if expression p can only be true if at least
** one column of table iTab is non-null. In other words, return true
** if expression p will always be NULL or false if every column of iTab
** is NULL.
**
** Terms of p that are marked with EP_FromJoin (and hence that come from
** the ON or USING clauses of LEFT JOINS) are excluded from the analysis.
**
** This routine is used to check if a LEFT JOIN can be converted into
** an ordinary JOIN. The p argument is the WHERE clause. If the WHERE
** clause requires that some column of the right table of the LEFT JOIN
** be non-NULL, then the LEFT JOIN can be safely converted into an
** ordinary join.
*/
int sqlite3ExprImpliesNonNullRow(Expr *p, int iTab){
Walker w;
w.xExprCallback = impliesNotNullRow;
w.xSelectCallback = 0;
w.xSelectCallback2 = 0;
w.eCode = 0;
w.u.iCur = iTab;
sqlite3WalkExpr(&w, p);
return w.eCode;
}
/*
** An instance of the following structure is used by the tree walker
** to determine if an expression can be evaluated by reference to the

40
src/select.c
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@ -382,6 +382,28 @@ static void setJoinExpr(Expr *p, int iTable){
}
}
/* Undo the work of setJoinExpr(). In the expression tree p, convert every
** term that is marked with EP_FromJoin and iRightJoinTable==iTable into
** an ordinary term that omits the EP_FromJoin mark.
**
** This happens when a LEFT JOIN is simplified into an ordinary JOIN.
*/
static void unsetJoinExpr(Expr *p, int iTable){
while( p ){
if( ExprHasProperty(p, EP_FromJoin) && p->iRightJoinTable==iTable ){
ExprClearProperty(p, EP_FromJoin);
}
if( p->op==TK_FUNCTION && p->x.pList ){
int i;
for(i=0; i<p->x.pList->nExpr; i++){
unsetJoinExpr(p->x.pList->a[i].pExpr, iTable);
}
}
unsetJoinExpr(p->pLeft, iTable);
p = p->pRight;
}
}
/*
** This routine processes the join information for a SELECT statement.
** ON and USING clauses are converted into extra terms of the WHERE clause.
@ -5175,13 +5197,29 @@ int sqlite3Select(
generateColumnNames(pParse, p);
}
/* Try to flatten subqueries in the FROM clause up into the main query
/* Try to various optimizations (flattening subqueries, and strength
** reduction of join operators) in the FROM clause up into the main query
*/
#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
for(i=0; !p->pPrior && i<pTabList->nSrc; i++){
struct SrcList_item *pItem = &pTabList->a[i];
Select *pSub = pItem->pSelect;
Table *pTab = pItem->pTab;
/* Convert LEFT JOIN into JOIN if there are terms of the right table
** of the LEFT JOIN used in the WHERE clause.
*/
if( (pItem->fg.jointype & JT_LEFT)!=0
&& sqlite3ExprImpliesNonNullRow(p->pWhere, pItem->iCursor)
&& OptimizationEnabled(db, SQLITE_SimplifyJoin)
){
SELECTTRACE(0x100,pParse,p,
("LEFT-JOIN simplifies to JOIN on term %d\n",i));
pItem->fg.jointype &= ~JT_LEFT;
unsetJoinExpr(p->pWhere, pItem->iCursor);
}
/* No futher action if this term of the FROM clause is no a subquery */
if( pSub==0 ) continue;
/* Catch mismatch in the declared columns of a view and the number of

2
src/sqliteInt.h
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@ -1533,6 +1533,7 @@ struct sqlite3 {
#define SQLITE_Stat34 0x0800 /* Use STAT3 or STAT4 data */
/* TH3 expects the Stat34 ^^^^^^ value to be 0x0800. Don't change it */
#define SQLITE_PushDown 0x1000 /* The push-down optimization */
#define SQLITE_SimplifyJoin 0x2000 /* Convert LEFT JOIN to JOIN */
#define SQLITE_AllOpts 0xffff /* All optimizations */
/*
@ -3823,6 +3824,7 @@ int sqlite3ExprCompare(Parse*,Expr*, Expr*, int);
int sqlite3ExprCompareSkip(Expr*, Expr*, int);
int sqlite3ExprListCompare(ExprList*, ExprList*, int);
int sqlite3ExprImpliesExpr(Parse*,Expr*, Expr*, int);
int sqlite3ExprImpliesNonNullRow(Expr*,int);
void sqlite3ExprAnalyzeAggregates(NameContext*, Expr*);
void sqlite3ExprAnalyzeAggList(NameContext*,ExprList*);
int sqlite3ExprCoveredByIndex(Expr*, int iCur, Index *pIdx);

2
test/e_select.test
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@ -748,7 +748,7 @@ do_execsql_test e_select-3.2.1a {
SELECT k FROM x1 LEFT JOIN x2 USING(k)
} {1 2 3 4 5 6}
do_execsql_test e_select-3.2.1b {
SELECT k FROM x1 LEFT JOIN x2 USING(k) WHERE x2.k
SELECT k FROM x1 LEFT JOIN x2 USING(k) WHERE x2.k ORDER BY +k
} {1 3 5}
do_execsql_test e_select-3.2.2 {
SELECT k FROM x1 LEFT JOIN x2 USING(k) WHERE x2.k IS NULL

2
test/join2.test
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@ -86,7 +86,7 @@ do_execsql_test 2.0 {
}
do_catchsql_test 2.1 {
SELECT * FROM aa LEFT JOIN cc ON (a=b) JOIN bb ON (b=c);
SELECT * FROM aa LEFT JOIN cc ON (a=b) JOIN bb ON (b=coalesce(c,1));
} {1 {ON clause references tables to its right}}
do_catchsql_test 2.2 {
SELECT * FROM aa JOIN cc ON (a=b) JOIN bb ON (b=c);