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Comment:  In the query planner, do not consider index X to be a proper subset of index Y if X is a covering index but Y is not. 

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User & Date:  drh 20171015 22:16:25 
20171016
 
11:50  Improved comments, including a typo fix, on the whereLoopCheaperProperSubset() function. (checkin: 700a3c69 user: drh tags: trunk)  
20171015
 
22:16  In the query planner, do not consider index X to be a proper subset of index Y if X is a covering index but Y is not. (checkin: ee31c043 user: drh tags: trunk)  
20171014
 
19:54  Updates to the Makefiles for MSVC. (checkin: ac8786f3 user: mistachkin tags: trunk)  
Changes to src/where.c.
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} } /* ** Return TRUE if all of the following are true: ** ** (1) X has the same or lower cost that Y ** (2) X is a proper subset of Y ** (3) X skips at least as many columns as Y ** ** By "proper subset" we mean that X uses fewer WHERE clause terms ** than Y and that every WHERE clause term used by X is also used ** by Y. ** ** If X is a proper subset of Y then Y is a better choice and ought ** to have a lower cost. This routine returns TRUE when that cost ** relationship is inverted and needs to be adjusted. The third rule ** was added because if X uses skipscan less than Y it still might ** deserve a lower cost even if it is a proper subset of Y. */ static int whereLoopCheaperProperSubset( const WhereLoop *pX, /* First WhereLoop to compare */ const WhereLoop *pY /* Compare against this WhereLoop */ ){ ................................................................................ } for(i=pX>nLTerm1; i>=0; i){ if( pX>aLTerm[i]==0 ) continue; for(j=pY>nLTerm1; j>=0; j){ if( pY>aLTerm[j]==pX>aLTerm[i] ) break; } if( j<0 ) return 0; /* X not a subset of Y since term X[i] not used by Y */ } return 1; /* All conditions meet */ } /* ** Try to adjust the cost of WhereLoop pTemplate upwards or downwards so ** that: 

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} } /* ** Return TRUE if all of the following are true: ** ** (1) X has the same or lower cost that Y ** (2) X users fewer WHERE clause terms than Y ** (3) Every WHERE clause term used by X is also used by Y ** (4) X skips at least as many columns as Y ** (5) If X is a covering index, than Y is too ** ** Conditions (2) and (3) mean that X is a "proper subset" of Y. ** If X is a proper subset of Y then Y is a better choice and ought ** to have a lower cost. This routine returns TRUE when that cost ** relationship is inverted and needs to be adjusted. Constraint (4) ** was added because if X uses skipscan less than Y it still might ** deserve a lower cost even if it is a proper subset of Y. */ static int whereLoopCheaperProperSubset( const WhereLoop *pX, /* First WhereLoop to compare */ const WhereLoop *pY /* Compare against this WhereLoop */ ){ ................................................................................ } for(i=pX>nLTerm1; i>=0; i){ if( pX>aLTerm[i]==0 ) continue; for(j=pY>nLTerm1; j>=0; j){ if( pY>aLTerm[j]==pX>aLTerm[i] ) break; } if( j<0 ) return 0; /* X not a subset of Y since term X[i] not used by Y */ } if( (pX>wsFlags&WHERE_IDX_ONLY)!=0 && (pY>wsFlags&WHERE_IDX_ONLY)==0 ){ return 0; /* Constraint (5) */ } return 1; /* All conditions meet */ } /* ** Try to adjust the cost of WhereLoop pTemplate upwards or downwards so ** that: 
Changes to test/analyze9.test.
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INSERT INTO t4 SELECT a, b, c, d, e, f FROM data;
ANALYZE;
} {}
do_eqp_test 23.1 {
SELECT * FROM t4 WHERE
(e=1 AND b='xyz' AND c='zyx' AND a<'AEA') AND f<300
} {
0 0 0 {SEARCH TABLE t4 USING INDEX i41 (e=? AND c=? AND b=? AND a<?)}
}
do_eqp_test 23.2 {
SELECT * FROM t4 WHERE
(e=1 AND b='xyz' AND c='zyx' AND a<'JJJ') AND f<300
} {
0 0 0 {SEARCH TABLE t4 USING INDEX i42 (f<?)}
}

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INSERT INTO t4 SELECT a, b, c, d, e, f FROM data; ANALYZE; } {} do_eqp_test 23.1 { SELECT * FROM t4 WHERE (e=1 AND b='xyz' AND c='zyx' AND a<'AEA') AND f<300  Formerly used index i41. But i41 is not a covering index whereas  the PRIMARY KEY is a covering index, and so as of 20171015, the  PRIMARY KEY is preferred. } { 0 0 0 {SEARCH TABLE t4 USING PRIMARY KEY (c=? AND b=? AND a<?)} } do_eqp_test 23.2 { SELECT * FROM t4 WHERE (e=1 AND b='xyz' AND c='zyx' AND a<'JJJ') AND f<300 } { 0 0 0 {SEARCH TABLE t4 USING INDEX i42 (f<?)} } 