Improved comments on the constraint checking logic.

FossilOrigin-Name: 141a38a7a636e3e4255b59c27df4a1b3d6f26e97

manifest

@@ -1,5 +1,5 @@
-C Merge\srecent\sfixes\sfrom\strunk.
+C Improved\scomments\son\sthe\sconstraint\schecking\slogic.
-D 2013-10-28T22:39:53.007
+D 2013-10-29T16:14:35.997
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 0522b53cdc1fcfc18f3a98e0246add129136c654
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -182,7 +182,7 @@ F src/global.c 5caf4deab621abb45b4c607aad1bd21c20aac759
 F src/hash.c ac3470bbf1ca4ae4e306a8ecb0fdf1731810ffe4
 F src/hash.h 8890a25af81fb85a9ad7790d32eedab4b994da22
 F src/hwtime.h d32741c8f4df852c7d959236615444e2b1063b08
-F src/insert.c 14ae816acbebd927bc070bf684de638f78cfccba
+F src/insert.c 42e8dc617c4db4683b4b2aac4d40dabf0333bef2
 F src/journal.c b4124532212b6952f42eb2c12fa3c25701d8ba8d
 F src/legacy.c 0df0b1550b9cc1f58229644735e317ac89131f12
 F src/lempar.c cdf0a000315332fc9b50b62f3b5e22e080a0952b
@@ -1127,7 +1127,7 @@ F tool/vdbe-compress.tcl f12c884766bd14277f4fcedcae07078011717381
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh d1a6de74685f360ab718efda6265994b99bbea01
 F tool/win/sqlite.vsix 030f3eeaf2cb811a3692ab9c14d021a75ce41fff
-P 086ec2a177b24ad90d5d705a99d93aa0c1545217 3a9e3ed94bf617f00c48009b1a6d348a8f23a3cf
+P 9f8191d1d833acaaf612fdff8cc6bd544c042986
-R 8a68d5fd17d8dcd9d86fb48741f61369
+R 1ffaeb4130b0ebfe6aa0338f8dfd6db1
 U drh
-Z c438434c68bedb89ea1b9008c1cfe6f8
+Z 4dc4c03fad5693ab5ce15641b23c251b

manifest.uuid

@@ -1 +1 @@
-9f8191d1d833acaaf612fdff8cc6bd544c042986
+141a38a7a636e3e4255b59c27df4a1b3d6f26e97

src/insert.c

@@ -1182,8 +1182,8 @@ static int sqlite3PrimaryKeyRegisters(Parse *pParse, Index *pPk, int regFirst){
 ** false for INSERTs. If isUpdate is false then a non-zero pkChng 
 ** indicates that the rowid was explicitly specified as part of the
 ** INSERT statement. If pkChng is false, it means that  the rowid is
-** computed automatically in an insert or that the rowid value is not 
+** computed automatically in an insert and is therefore guaranteed to
-** modified by an update. The pkChng parameter is always false for inserts
+** be unique. The pkChng parameter is always false for inserts
 ** into a WITHOUT ROWID table.
 **
 ** The code generated by this routine should store new index entries into
@@ -1275,6 +1275,7 @@ void sqlite3GenerateConstraintChecks(
   /* For WITHOUT ROWID tables, we'll need to know the Index and the cursor
   ** number for the PRIMARY KEY index */
   if( !HasRowid(pTab) ){
+    assert( pkChng==0 || isUpdate!=0 );
     pkCur = baseCur+1;
     pPk = pTab->pIndex;
     while( ALWAYS(pPk) && pPk->autoIndex!=2 ){
@@ -1304,6 +1305,7 @@ void sqlite3GenerateConstraintChecks(
     switch( onError ){
       case OE_Abort:
         sqlite3MayAbort(pParse);
+        /* Fall through */
       case OE_Rollback:
       case OE_Fail: {
         char *zMsg;
@@ -1356,7 +1358,7 @@ void sqlite3GenerateConstraintChecks(
   }
 #endif /* !defined(SQLITE_OMIT_CHECK) */
 
-  /* If we have an INTEGER PRIMARY KEY, make sure the primary key
+  /* If there is an INTEGER PRIMARY KEY, make sure the primary key
   ** of the new record does not previously exist.  Except, if this
   ** is an UPDATE and the primary key is not changing, that is OK.
   **
@@ -1446,7 +1448,7 @@ void sqlite3GenerateConstraintChecks(
     int idxCur = baseCur+iCur+1;
     int addrUniqueOk = sqlite3VdbeMakeLabel(v);
 
-    if( aRegIdx[iCur]==0 ) continue;  /* Skip unused indices */
+    if( aRegIdx[iCur]==0 ) continue;  /* Skip indices that do not change */
 
     if( pIdx->pPartIdxWhere ){
       sqlite3VdbeAddOp2(v, OP_Null, 0, aRegIdx[iCur]);
@@ -1491,13 +1493,21 @@ void sqlite3GenerateConstraintChecks(
     regR = sqlite3GetTempReg(pParse);
     sqlite3VdbeAddOp4Int(v, OP_NoConflict, idxCur, addrUniqueOk,
                          regIdx, pIdx->nKeyCol);
+#if 0
+    if( !isUpdate ){
+      /* A pre-existing row is always a conflict on an insert */
+    }else
+#endif
     if( HasRowid(pTab) ){
-      /* Conflict only if the rowid of the existing entry with the matching
+      /* Conflict only if the rowid of the existing index entry
-      ** key is different from old-rowid */
+      ** is different from old-rowid */
       sqlite3VdbeAddOp2(v, OP_IdxRowid, idxCur, regR);
       sqlite3VdbeAddOp3(v, OP_Eq, regR, addrUniqueOk, regOldPk);
     }else if( pIdx->autoIndex==2 ){
-      /* If there is a matching entry on the PRIMARY KEY index ... */
+      /* For PRIMARY KEY index on a WITHOUT ROWID table, conflict only
+      ** if the PRIMARY KEY has changed.  If the PRIMARY KEY is unchanged,
+      ** then the matching entry is just the original row that is being
+      ** modified. */
       int addrPkConflict = sqlite3VdbeCurrentAddr(v)+pPk->nKeyCol;
       for(i=0; i<pPk->nKeyCol-1; i++){
         sqlite3VdbeAddOp3(v, OP_Ne,
@@ -1506,6 +1516,9 @@ void sqlite3GenerateConstraintChecks(
       sqlite3VdbeAddOp3(v, OP_Eq,
                         regOldPk+pPk->aiColumn[i], addrUniqueOk, regIdx+i);
     }else{
+      /* For a UNIQUE index on a WITHOUT ROWID table, conflict only if the
+      ** PRIMARY KEY value of the match is different from the old PRIMARY KEY
+      ** value from before the update. */
       int addrConflict = sqlite3VdbeCurrentAddr(v)+pPk->nKeyCol*2;
       assert( pIdx->nKeyCol + pPk->nKeyCol == pIdx->nColumn );
       for(i=0; i<pPk->nKeyCol-1; i++){