Adding the "noskipscan" token to an sqlite_stat1.stat field prevents

an index for being used with the skip-scan algorithm.

FossilOrigin-Name: 4461bf045d8eecf98478035efcdba3f41c709bc5

src/analyze.c

@@ -1466,6 +1466,8 @@ static void decodeIntArray(
       pIndex->bUnordered = 1;
     }else if( sqlite3_strglob("sz=[0-9]*", z)==0 ){
       pIndex->szIdxRow = sqlite3LogEst(sqlite3Atoi(z+3));
+    }else if( sqlite3_strglob("noskipscan*", z)==0 ){
+      pIndex->noSkipScan = 1;
     }
 #ifdef SQLITE_ENABLE_COSTMULT
     else if( sqlite3_strglob("costmult=[0-9]*",z)==0 ){

src/sqliteInt.h

@@ -1795,6 +1795,7 @@ struct Index {
   unsigned uniqNotNull:1;  /* True if UNIQUE and NOT NULL for all columns */
   unsigned isResized:1;    /* True if resizeIndexObject() has been called */
   unsigned isCovering:1;   /* True if this is a covering index */
+  unsigned noSkipScan:1;   /* Do not try to use skip-scan if true */
 #ifdef SQLITE_ENABLE_STAT3_OR_STAT4
   int nSample;             /* Number of elements in aSample[] */
   int nSampleCol;          /* Size of IndexSample.anEq[] and so on */

src/where.c

@@ -4588,6 +4588,7 @@ static int whereLoopAddBtreeIndex(
   assert( 42==sqlite3LogEst(18) );
   if( saved_nEq==saved_nSkip
    && saved_nEq+1<pProbe->nKeyCol
+   && pProbe->noSkipScan==0
    && pProbe->aiRowLogEst[saved_nEq+1]>=42  /* TUNING: Minimum for skip-scan */
    && (rc = whereLoopResize(db, pNew, pNew->nLTerm+1))==SQLITE_OK
   ){