1 /*

     2 ** 2001 September 15

     3 **

     4 ** The author disclaims copyright to this source code.  In place of

     5 ** a legal notice, here is a blessing:

     6 **

     7 **    May you do good and not evil.

     8 **    May you find forgiveness for yourself and forgive others.

     9 **    May you share freely, never taking more than you give.

    10 **

    11 *************************************************************************

    12 ** This file contains C code routines that are called by the parser

    13 ** in order to generate code for DELETE FROM statements.

    14 **

    15 ** $Id: delete.cpp 1282 2008-11-13 09:31:33Z LarsPson $

    16 */

    17 #include "sqliteInt.h"

    18 

    19 /*

    20 ** Look up every table that is named in pSrc.  If any table is not found,

    21 ** add an error message to pParse->zErrMsg and return NULL.  If all tables

    22 ** are found, return a pointer to the last table.

    23 */

    24 Table *sqlite3SrcListLookup(Parse *pParse, SrcList *pSrc){

    25   Table *pTab = 0;

    26   int i;

    27   SrcList::SrcList_item *pItem;

    28   for(i=0, pItem=pSrc->a; i<pSrc->nSrc; i++, pItem++){

    29     pTab = sqlite3LocateTable(pParse, pItem->zName, pItem->zDatabase);

    30     sqlite3DeleteTable(pItem->pTab);

    31     pItem->pTab = pTab;

    32     if( pTab ){

    33       pTab->nRef++;

    34     }

    35   }

    36   return pTab;

    37 }

    38 

    39 /*

    40 ** Check to make sure the given table is writable.  If it is not

    41 ** writable, generate an error message and return 1.  If it is

    42 ** writable return 0;

    43 */

    44 int sqlite3IsReadOnly(Parse *pParse, Table *pTab, int viewOk){

    45   if( (pTab->readOnly && (pParse->db->flags & SQLITE_WriteSchema)==0

    46         && pParse->nested==0) 

    47 #ifndef SQLITE_OMIT_VIRTUALTABLE

    48       || (pTab->pMod && pTab->pMod->pModule->xUpdate==0)

    49 #endif

    50   ){

    51     sqlite3ErrorMsg(pParse, "table %s may not be modified", pTab->zName);

    52     return 1;

    53   }

    54 #ifndef SQLITE_OMIT_VIEW

    55   if( !viewOk && pTab->pSelect ){

    56     sqlite3ErrorMsg(pParse,"cannot modify %s because it is a view",pTab->zName);

    57     return 1;

    58   }

    59 #endif

    60   return 0;

    61 }

    62 

    63 /*

    64 ** Generate code that will open a table for reading.

    65 */

    66 void sqlite3OpenTable(

    67   Parse *p,       /* Generate code into this VDBE */

    68   int iCur,       /* The cursor number of the table */

    69   int iDb,        /* The database index in sqlite3.aDb[] */

    70   Table *pTab,    /* The table to be opened */

    71   int opcode      /* OP_OpenRead or OP_OpenWrite */

    72 ){

    73   Vdbe *v;

    74   if( IsVirtual(pTab) ) return;

    75   v = sqlite3GetVdbe(p);

    76   assert( opcode==OP_OpenWrite || opcode==OP_OpenRead );

    77   sqlite3TableLock(p, iDb, pTab->tnum, (opcode==OP_OpenWrite), pTab->zName);

    78   sqlite3VdbeAddOp(v, OP_Integer, iDb, 0);

    79   VdbeComment((v, "# %s", pTab->zName));

    80   sqlite3VdbeAddOp(v, opcode, iCur, pTab->tnum);

    81   sqlite3VdbeAddOp(v, OP_SetNumColumns, iCur, pTab->nCol);

    82 }

    83 

    84 

    85 /*

    86 ** Generate code for a DELETE FROM statement.

    87 **

    88 **     DELETE FROM table_wxyz WHERE a<5 AND b NOT NULL;

    89 **                 \________/       \________________/

    90 **                  pTabList              pWhere

    91 */

    92 void sqlite3DeleteFrom(

    93   Parse *pParse,         /* The parser context */

    94   SrcList *pTabList,     /* The table from which we should delete things */

    95   Expr *pWhere           /* The WHERE clause.  May be null */

    96 ){

    97   Vdbe *v;               /* The virtual database engine */

    98   Table *pTab;           /* The table from which records will be deleted */

    99   const char *zDb;       /* Name of database holding pTab */

   100   int end, addr = 0;     /* A couple addresses of generated code */

   101   int i;                 /* Loop counter */

   102   WhereInfo *pWInfo;     /* Information about the WHERE clause */

   103   Index *pIdx;           /* For looping over indices of the table */

   104   int iCur;              /* VDBE Cursor number for pTab */

   105   sqlite3 *db;           /* Main database structure */

   106   AuthContext sContext;  /* Authorization context */

   107   int oldIdx = -1;       /* Cursor for the OLD table of AFTER triggers */

   108   NameContext sNC;       /* Name context to resolve expressions in */

   109   int iDb;               /* Database number */

   110   int memCnt = 0;        /* Memory cell used for change counting */

   111 

   112 #ifndef SQLITE_OMIT_TRIGGER

   113   int isView;                  /* True if attempting to delete from a view */

   114   int triggers_exist = 0;      /* True if any triggers exist */

   115 #endif

   116 

   117   sContext.pParse = 0;

   118   db = pParse->db;

   119   if( pParse->nErr || db->mallocFailed ){

   120     goto delete_from_cleanup;

   121   }

   122   assert( pTabList->nSrc==1 );

   123 

   124   /* Locate the table which we want to delete.  This table has to be

   125   ** put in an SrcList structure because some of the subroutines we

   126   ** will be calling are designed to work with multiple tables and expect

   127   ** an SrcList* parameter instead of just a Table* parameter.

   128   */

   129   pTab = sqlite3SrcListLookup(pParse, pTabList);

   130   if( pTab==0 )  goto delete_from_cleanup;

   131 

   132   /* Figure out if we have any triggers and if the table being

   133   ** deleted from is a view

   134   */

   135 #ifndef SQLITE_OMIT_TRIGGER

   136   triggers_exist = sqlite3TriggersExist(pParse, pTab, TK_DELETE, 0);

   137   isView = pTab->pSelect!=0;

   138 #else

   139 # define triggers_exist 0

   140 # define isView 0

   141 #endif

   142 #ifdef SQLITE_OMIT_VIEW

   143 # undef isView

   144 # define isView 0

   145 #endif

   146 

   147   if( sqlite3IsReadOnly(pParse, pTab, triggers_exist) ){

   148     goto delete_from_cleanup;

   149   }

   150   iDb = sqlite3SchemaToIndex(db, pTab->pSchema);

   151   assert( iDb<db->nDb );

   152   zDb = db->aDb[iDb].zName;

   153   if( sqlite3AuthCheck(pParse, SQLITE_DELETE, pTab->zName, 0, zDb) ){

   154     goto delete_from_cleanup;

   155   }

   156 

   157   /* If pTab is really a view, make sure it has been initialized.

   158   */

   159   if( sqlite3ViewGetColumnNames(pParse, pTab) ){

   160     goto delete_from_cleanup;

   161   }

   162 

   163   /* Allocate a cursor used to store the old.* data for a trigger.

   164   */

   165   if( triggers_exist ){ 

   166     oldIdx = pParse->nTab++;

   167   }

   168 

   169   /* Resolve the column names in the WHERE clause.

   170   */

   171   assert( pTabList->nSrc==1 );

   172   iCur = pTabList->a[0].iCursor = pParse->nTab++;

   173   memset(&sNC, 0, sizeof(sNC));

   174   sNC.pParse = pParse;

   175   sNC.pSrcList = pTabList;

   176   if( sqlite3ExprResolveNames(&sNC, pWhere) ){

   177     goto delete_from_cleanup;

   178   }

   179 

   180   /* Start the view context

   181   */

   182   if( isView ){

   183     sqlite3AuthContextPush(pParse, &sContext, pTab->zName);

   184   }

   185 

   186   /* Begin generating code.

   187   */

   188   v = sqlite3GetVdbe(pParse);

   189   if( v==0 ){

   190     goto delete_from_cleanup;

   191   }

   192   if( pParse->nested==0 ) sqlite3VdbeCountChanges(v);

   193   sqlite3BeginWriteOperation(pParse, triggers_exist, iDb);

   194 

   195   /* If we are trying to delete from a view, realize that view into

   196   ** a ephemeral table.

   197   */

   198   if( isView ){

   199     Select *pView = sqlite3SelectDup(db, pTab->pSelect);

   200     sqlite3Select(pParse, pView, SRT_EphemTab, iCur, 0, 0, 0, 0);

   201     sqlite3SelectDelete(pView);

   202   }

   203 

   204   /* Initialize the counter of the number of rows deleted, if

   205   ** we are counting rows.

   206   */

   207   if( db->flags & SQLITE_CountRows ){

   208     memCnt = pParse->nMem++;

   209     sqlite3VdbeAddOp(v, OP_MemInt, 0, memCnt);

   210   }

   211 

   212   /* Special case: A DELETE without a WHERE clause deletes everything.

   213   ** It is easier just to erase the whole table.  Note, however, that

   214   ** this means that the row change count will be incorrect.

   215   */

   216   if( pWhere==0 && !triggers_exist && !IsVirtual(pTab) ){

   217     if( db->flags & SQLITE_CountRows ){

   218       /* If counting rows deleted, just count the total number of

   219       ** entries in the table. */

   220       int addr2;

   221       if( !isView ){

   222         sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenRead);

   223       }

   224       sqlite3VdbeAddOp(v, OP_Rewind, iCur, sqlite3VdbeCurrentAddr(v)+2);

   225       addr2 = sqlite3VdbeAddOp(v, OP_MemIncr, 1, memCnt);

   226       sqlite3VdbeAddOp(v, OP_Next, iCur, addr2);

   227       sqlite3VdbeAddOp(v, OP_Close, iCur, 0);

   228     }

   229     if( !isView ){

   230       sqlite3VdbeAddOp(v, OP_Clear, pTab->tnum, iDb);

   231       if( !pParse->nested ){

   232         sqlite3VdbeChangeP3(v, -1, pTab->zName, P3_STATIC);

   233       }

   234       for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){

   235         assert( pIdx->pSchema==pTab->pSchema );

   236         sqlite3VdbeAddOp(v, OP_Clear, pIdx->tnum, iDb);

   237       }

   238     }

   239   } 

   240   /* The usual case: There is a WHERE clause so we have to scan through

   241   ** the table and pick which records to delete.

   242   */

   243   else{

   244     /* Begin the database scan

   245     */

   246     pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0);

   247     if( pWInfo==0 ) goto delete_from_cleanup;

   248 

   249     /* Remember the rowid of every item to be deleted.

   250     */

   251     sqlite3VdbeAddOp(v, IsVirtual(pTab) ? OP_VRowid : OP_Rowid, iCur, 0);

   252     sqlite3VdbeAddOp(v, OP_FifoWrite, 0, 0);

   253     if( db->flags & SQLITE_CountRows ){

   254       sqlite3VdbeAddOp(v, OP_MemIncr, 1, memCnt);

   255     }

   256 

   257     /* End the database scan loop.

   258     */

   259     sqlite3WhereEnd(pWInfo);

   260 

   261     /* Open the pseudo-table used to store OLD if there are triggers.

   262     */

   263     if( triggers_exist ){

   264       sqlite3VdbeAddOp(v, OP_OpenPseudo, oldIdx, 0);

   265       sqlite3VdbeAddOp(v, OP_SetNumColumns, oldIdx, pTab->nCol);

   266     }

   267 

   268     /* Delete every item whose key was written to the list during the

   269     ** database scan.  We have to delete items after the scan is complete

   270     ** because deleting an item can change the scan order.

   271     */

   272     end = sqlite3VdbeMakeLabel(v);

   273 

   274     /* This is the beginning of the delete loop when there are

   275     ** row triggers.

   276     */

   277     if( triggers_exist ){

   278       int mem1 = pParse->nMem++;

   279       addr = sqlite3VdbeAddOp(v, OP_FifoRead, 0, end);

   280       sqlite3VdbeAddOp(v, OP_StackDepth, -1, 0);

   281       sqlite3VdbeAddOp(v, OP_MemStore, mem1, 0);

   282       if( !isView ){

   283         sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenRead);

   284       }

   285       sqlite3VdbeAddOp(v, OP_NotExists, iCur, addr);

   286       sqlite3VdbeAddOp(v, OP_Rowid, iCur, 0);

   287       sqlite3VdbeAddOp(v, OP_RowData, iCur, 0);

   288       sqlite3VdbeAddOp(v, OP_Insert, oldIdx, 0);

   289       if( !isView ){

   290         sqlite3VdbeAddOp(v, OP_Close, iCur, 0);

   291       }

   292 

   293       (void)sqlite3CodeRowTrigger(pParse, TK_DELETE, 0, TRIGGER_BEFORE, pTab,

   294           -1, oldIdx, (pParse->trigStack)?pParse->trigStack->orconf:OE_Default,

   295           addr);

   296       if( !isView ){

   297         sqlite3VdbeAddOp(v, OP_MemLoad, mem1, 0);

   298       }

   299     }

   300 

   301     if( !isView ){

   302       /* Open cursors for the table we are deleting from and all its

   303       ** indices.  If there are row triggers, this happens inside the

   304       ** OP_FifoRead loop because the cursor have to all be closed

   305       ** before the trigger fires.  If there are no row triggers, the

   306       ** cursors are opened only once on the outside the loop.

   307       */

   308       sqlite3OpenTableAndIndices(pParse, pTab, iCur, OP_OpenWrite);

   309 

   310       /* This is the beginning of the delete loop when there are no

   311       ** row triggers */

   312       if( !triggers_exist ){ 

   313         addr = sqlite3VdbeAddOp(v, OP_FifoRead, 0, end);

   314         sqlite3VdbeAddOp(v, OP_StackDepth, -1, 0);

   315       }

   316 

   317       /* Delete the row */

   318 #ifndef SQLITE_OMIT_VIRTUALTABLE

   319       if( IsVirtual(pTab) ){

   320         pParse->pVirtualLock = pTab;

   321         sqlite3VdbeOp3(v, OP_VUpdate, 0, 1, (const char*)pTab->pVtab, P3_VTAB);

   322       }else

   323 #endif

   324       {

   325         sqlite3GenerateRowDelete(db, v, pTab, iCur, pParse->nested==0);

   326       }

   327     }

   328 

   329     /* If there are row triggers, close all cursors then invoke

   330     ** the AFTER triggers

   331     */

   332     if( triggers_exist ){

   333       if( !isView ){

   334         for(i=1, pIdx=pTab->pIndex; pIdx; i++, pIdx=pIdx->pNext){

   335           sqlite3VdbeAddOp(v, OP_Close, iCur + i, pIdx->tnum);

   336         }

   337         sqlite3VdbeAddOp(v, OP_Close, iCur, 0);

   338       }

   339       (void)sqlite3CodeRowTrigger(pParse, TK_DELETE, 0, TRIGGER_AFTER, pTab, -1,

   340           oldIdx, (pParse->trigStack)?pParse->trigStack->orconf:OE_Default,

   341           addr);

   342     }

   343 

   344     /* End of the delete loop */

   345     sqlite3VdbeAddOp(v, OP_Goto, 0, addr);

   346     sqlite3VdbeResolveLabel(v, end);

   347 

   348     /* Close the cursors after the loop if there are no row triggers */

   349     if( !triggers_exist && !IsVirtual(pTab) ){

   350       for(i=1, pIdx=pTab->pIndex; pIdx; i++, pIdx=pIdx->pNext){

   351         sqlite3VdbeAddOp(v, OP_Close, iCur + i, pIdx->tnum);

   352       }

   353       sqlite3VdbeAddOp(v, OP_Close, iCur, 0);

   354     }

   355   }

   356 

   357   /*

   358   ** Return the number of rows that were deleted. If this routine is 

   359   ** generating code because of a call to sqlite3NestedParse(), do not

   360   ** invoke the callback function.

   361   */

   362   if( db->flags & SQLITE_CountRows && pParse->nested==0 && !pParse->trigStack ){

   363     sqlite3VdbeAddOp(v, OP_MemLoad, memCnt, 0);

   364     sqlite3VdbeAddOp(v, OP_Callback, 1, 0);

   365     sqlite3VdbeSetNumCols(v, 1);

   366     sqlite3VdbeSetColName(v, 0, COLNAME_NAME, "rows deleted", P3_STATIC);

   367   }

   368 

   369 delete_from_cleanup:

   370   sqlite3AuthContextPop(&sContext);

   371   sqlite3SrcListDelete(pTabList);

   372   sqlite3ExprDelete(pWhere);

   373   return;

   374 }

   375 

   376 /*

   377 ** This routine generates VDBE code that causes a single row of a

   378 ** single table to be deleted.

   379 **

   380 ** The VDBE must be in a particular state when this routine is called.

   381 ** These are the requirements:

   382 **

   383 **   1.  A read/write cursor pointing to pTab, the table containing the row

   384 **       to be deleted, must be opened as cursor number "base".

   385 **

   386 **   2.  Read/write cursors for all indices of pTab must be open as

   387 **       cursor number base+i for the i-th index.

   388 **

   389 **   3.  The record number of the row to be deleted must be on the top

   390 **       of the stack.

   391 **

   392 ** This routine pops the top of the stack to remove the record number

   393 ** and then generates code to remove both the table record and all index

   394 ** entries that point to that record.

   395 */

   396 void sqlite3GenerateRowDelete(

   397   sqlite3 *db,       /* The database containing the index */

   398   Vdbe *v,           /* Generate code into this VDBE */

   399   Table *pTab,       /* Table containing the row to be deleted */

   400   int iCur,          /* Cursor number for the table */

   401   int count          /* Increment the row change counter */

   402 ){

   403   int addr;

   404   addr = sqlite3VdbeAddOp(v, OP_NotExists, iCur, 0);

   405   sqlite3GenerateRowIndexDelete(v, pTab, iCur, 0);

   406   sqlite3VdbeAddOp(v, OP_Delete, iCur, (count?OPFLAG_NCHANGE:0));

   407   if( count ){

   408     sqlite3VdbeChangeP3(v, -1, pTab->zName, P3_STATIC);

   409   }

   410   sqlite3VdbeJumpHere(v, addr);

   411 }

   412 

   413 /*

   414 ** This routine generates VDBE code that causes the deletion of all

   415 ** index entries associated with a single row of a single table.

   416 **

   417 ** The VDBE must be in a particular state when this routine is called.

   418 ** These are the requirements:

   419 **

   420 **   1.  A read/write cursor pointing to pTab, the table containing the row

   421 **       to be deleted, must be opened as cursor number "iCur".

   422 **

   423 **   2.  Read/write cursors for all indices of pTab must be open as

   424 **       cursor number iCur+i for the i-th index.

   425 **

   426 **   3.  The "iCur" cursor must be pointing to the row that is to be

   427 **       deleted.

   428 */

   429 void sqlite3GenerateRowIndexDelete(

   430   Vdbe *v,           /* Generate code into this VDBE */

   431   Table *pTab,       /* Table containing the row to be deleted */

   432   int iCur,          /* Cursor number for the table */

   433   char *aIdxUsed     /* Only delete if aIdxUsed!=0 && aIdxUsed[i]!=0 */

   434 ){

   435   int i;

   436   Index *pIdx;

   437 

   438   for(i=1, pIdx=pTab->pIndex; pIdx; i++, pIdx=pIdx->pNext){

   439     if( aIdxUsed!=0 && aIdxUsed[i-1]==0 ) continue;

   440     sqlite3GenerateIndexKey(v, pIdx, iCur);

   441     sqlite3VdbeAddOp(v, OP_IdxDelete, iCur+i, 0);

   442   }

   443 }

   444 

   445 /*

   446 ** Generate code that will assemble an index key and put it on the top

   447 ** of the tack.  The key with be for index pIdx which is an index on pTab.

   448 ** iCur is the index of a cursor open on the pTab table and pointing to

   449 ** the entry that needs indexing.

   450 */

   451 void sqlite3GenerateIndexKey(

   452   Vdbe *v,           /* Generate code into this VDBE */

   453   Index *pIdx,       /* The index for which to generate a key */

   454   int iCur           /* Cursor number for the pIdx->pTable table */

   455 ){

   456   int j;

   457   Table *pTab = pIdx->pTable;

   458 

   459   sqlite3VdbeAddOp(v, OP_Rowid, iCur, 0);

   460   for(j=0; j<pIdx->nColumn; j++){

   461     int idx = pIdx->aiColumn[j];

   462     if( idx==pTab->iPKey ){

   463       sqlite3VdbeAddOp(v, OP_Dup, j, 0);

   464     }else{

   465       sqlite3VdbeAddOp(v, OP_Column, iCur, idx);

   466       sqlite3ColumnDefault(v, pTab, idx);

   467     }

   468   }

   469   sqlite3VdbeAddOp(v, OP_MakeIdxRec, pIdx->nColumn, 0);

   470   sqlite3IndexAffinityStr(v, pIdx);

   471 }