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Enhance the comment on whereLoopAddBtree(). No changes to code.

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FossilOrigin-Name: b22dd165da227a52d88b17a91e80a1701dce61ad
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drh
2014-07-22 12:05:32 +00:00
parent 53ad7e48ab
commit 83a305f20e
3 changed files with 15 additions and 7 deletions
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8
src/where.c
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@@ -4577,6 +4577,14 @@ static int whereUsablePartialIndex(int iTab, WhereClause *pWC, Expr *pWhere){
** Normally, nSeek is 1. nSeek values greater than 1 come about if the
** WHERE clause includes "x IN (....)" terms used in place of "x=?". Or when
** implicit "x IN (SELECT x FROM tbl)" terms are added for skip-scans.
**
** The estimated values (nRow, nVisit, nSeek) often contain a large amount
** of uncertainty. For this reason, scoring is designed to pick plans that
** "do the least harm" if the estimates are inaccurate. For example, a
** log(nRow) factor is omitted from a non-covering index scan in order to
** bias the scoring in favor of using an index, since the worst-case
** performance of using an index is far better than the worst-case performance
** of a full table scan.
*/
static int whereLoopAddBtree(
WhereLoopBuilder *pBuilder, /* WHERE clause information */