diff options
Diffstat (limited to 'ext/misc/explain.c')
| -rw-r--r-- | ext/misc/explain.c | 34 |
1 files changed, 23 insertions, 11 deletions
diff --git a/ext/misc/explain.c b/ext/misc/explain.c index dc0c9d766..7a2fc4776 100644 --- a/ext/misc/explain.c +++ b/ext/misc/explain.c @@ -18,6 +18,10 @@ ** .load ./explain ** SELECT p2 FROM explain('SELECT * FROM sqlite_master') ** WHERE opcode='OpenRead'; +** +** This module was originally written to help simplify SQLite testing, +** by providing an easier means of verifying certain patterns in the +** generated bytecode. */ #if !defined(SQLITEINT_H) #include "sqlite3ext.h" @@ -232,23 +236,31 @@ static int explainBestIndex( sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo ){ - int i; + int i; /* Loop counter */ + int idx = -1; /* Index of a usable == constraint against SQL */ + int unusable = 0; /* True if there are unusable constraints on SQL */ - pIdxInfo->estimatedCost = (double)1000000; pIdxInfo->estimatedRows = 500; for(i=0; i<pIdxInfo->nConstraint; i++){ struct sqlite3_index_constraint *p = &pIdxInfo->aConstraint[i]; - if( p->usable - && p->iColumn==EXPLN_COLUMN_SQL - && p->op==SQLITE_INDEX_CONSTRAINT_EQ - ){ - pIdxInfo->estimatedCost = 10.0; - pIdxInfo->idxNum = 1; - pIdxInfo->aConstraintUsage[i].argvIndex = 1; - pIdxInfo->aConstraintUsage[i].omit = 1; - break; + if( p->iColumn!=EXPLN_COLUMN_SQL ) continue; + if( !p->usable ){ + unusable = 1; + }else if( p->op==SQLITE_INDEX_CONSTRAINT_EQ ){ + idx = i; } } + if( idx>=0 ){ + /* There exists a usable == constraint against the SQL column */ + pIdxInfo->estimatedCost = 10.0; + pIdxInfo->idxNum = 1; + pIdxInfo->aConstraintUsage[idx].argvIndex = 1; + pIdxInfo->aConstraintUsage[idx].omit = 1; + }else if( unusable ){ + /* There are unusable constraints against the SQL column. Do not allow + ** this plan to continue forward. */ + return SQLITE_CONSTRAINT; + } return SQLITE_OK; } |