Avoid redundant table b-tree cursor seeks in UPDATE statements that use the

two-pass strategy.

FossilOrigin-Name: dc555b1039c6930f6d15355c698ff917a85e8056

src/sqliteInt.h

@@ -2592,7 +2592,7 @@ struct SrcList {
 #define WHERE_SORTBYGROUP      0x0200 /* Support sqlite3WhereIsSorted() */
 #define WHERE_SEEK_TABLE       0x0400 /* Do not defer seeks on main table */
 #define WHERE_ORDERBY_LIMIT    0x0800 /* ORDERBY+LIMIT on the inner loop */
-                        /*     0x1000    not currently used */
+#define WHERE_SEEK_UNIQ_TABLE  0x1000 /* Do not defer seeks if unique */
                         /*     0x2000    not currently used */
 #define WHERE_USE_LIMIT        0x4000 /* Use the LIMIT in cost estimates */
                         /*     0x8000    not currently used */

src/update.c

@@ -392,7 +392,7 @@ void sqlite3Update(
   ** be deleted as a result of REPLACE conflict handling. Any of these
   ** things might disturb a cursor being used to scan through the table
   ** or index, causing a single-pass approach to malfunction.  */
-  flags = WHERE_ONEPASS_DESIRED | WHERE_SEEK_TABLE;
+  flags = WHERE_ONEPASS_DESIRED|WHERE_SEEK_UNIQ_TABLE;
   if( !pParse->nested && !pTrigger && !hasFK && !chngKey && !bReplace ){
     flags |= WHERE_ONEPASS_MULTIROW;
   }

src/wherecode.c

@@ -1591,7 +1591,10 @@ Bitmask sqlite3WhereCodeOneLoopStart(
     if( omitTable ){
       /* pIdx is a covering index.  No need to access the main table. */
     }else if( HasRowid(pIdx->pTable) ){
-      if( (pWInfo->wctrlFlags & WHERE_SEEK_TABLE)!=0 ){
+      if( (pWInfo->wctrlFlags & WHERE_SEEK_TABLE) || (
+          (pWInfo->wctrlFlags & WHERE_SEEK_UNIQ_TABLE) 
+       && (pWInfo->eOnePass==ONEPASS_SINGLE)
+      )){
         iRowidReg = ++pParse->nMem;
         sqlite3VdbeAddOp2(v, OP_IdxRowid, iIdxCur, iRowidReg);
         sqlite3ExprCacheStore(pParse, iCur, -1, iRowidReg);