SQLite

    sqlite3BeginWriteOperation(pParse, 1, iDb);

#ifndef SQLITE_OMIT_VIRTUALTABLE
    if( IsVirtual(pTab) ){
      sqlite3VdbeAddOp0(v, OP_VBegin);
    }
#endif
    sqlite3FkDropTable(pParse, pName, pTab);

    /* Drop all triggers associated with the table being dropped. Code
    ** is generated to remove entries from sqlite_master and/or
    ** sqlite_temp_master if required.
    */
    pTrigger = sqlite3TriggerList(pParse, pTab);
    while( pTrigger ){

    sqlite3ExprDelete(dbMem, pStep->pWhere);
    sqlite3ExprListDelete(dbMem, pStep->pExprList);
    sqlite3SelectDelete(dbMem, pStep->pSelect);
    sqlite3ExprDelete(dbMem, p->pWhen);
    sqlite3DbFree(dbMem, p);
  }
}

/*
** This function is called to generate code that runs when table pTab is
** being dropped from the database. The SrcList passed as the second argument
** to this function contains a single entry guaranteed to resolve to
** table pTab.
**
** Normally, no code is required. However, if either
**
**   (a) The table is the parent table of a FK constraint, or
**   (b) The table is the child table of a deferred FK constraint and it is
**       determined at runtime that there are outstanding deferred FK 
**       constraint violations in the database,
**
** then the equivalent of "DELETE FROM <tbl>" is executed before dropping
** the table from the database. Triggers are disabled while running this
** DELETE, but foreign key actions are not.
*/
void sqlite3FkDropTable(Parse *pParse, SrcList *pName, Table *pTab){
  sqlite3 *db = pParse->db;
  if( (db->flags&SQLITE_ForeignKeys) && !IsVirtual(pTab) && !pTab->pSelect ){
    int iSkip = 0;
    Vdbe *v = sqlite3GetVdbe(pParse);

    assert( v );                  /* VDBE has already been allocated */
    if( sqlite3FkReferences(pTab)==0 ){
      /* Search for a deferred foreign key constraint for which this table
      ** is the child table. If one cannot be found, return without 
      ** generating any VDBE code. If one can be found, then jump over
      ** the entire DELETE if there are no outstanding deferred constraints
      ** when this statement is run.  */
      FKey *p;
      for(p=pTab->pFKey; p; p=p->pNextFrom){
        if( p->isDeferred ) break;
      }
      if( !p ) return;
      iSkip = sqlite3VdbeMakeLabel(v);
      sqlite3VdbeAddOp2(v, OP_FkIfZero, 1, iSkip);
    }

    pParse->disableTriggers = 1;
    sqlite3DeleteFrom(pParse, sqlite3SrcListDup(db, pName, 0), 0);
    pParse->disableTriggers = 0;

    /* If the DELETE has generated immediate foreign key constraint 
    ** violations, halt the VDBE and return an error at this point, before
    ** any modifications to the schema are made. This is because statement
    ** transactions are not able to rollback schema changes.  */
    sqlite3VdbeAddOp2(v, OP_FkIfZero, 0, sqlite3VdbeCurrentAddr(v)+2);
    sqlite3HaltConstraint(
        pParse, OE_Abort, "foreign key constraint failed", P4_STATIC
    );

    if( iSkip ){
      sqlite3VdbeResolveLabel(v, iSkip);
    }
  }
}

/*
** This function is called when inserting, deleting or updating a row of
** table pTab to generate VDBE code to perform foreign key constraint 
** processing for the operation.
**
** For a DELETE operation, parameter regOld is passed the index of the

  /* Information used while coding trigger programs. */
  Parse *pToplevel;    /* Parse structure for main program (or NULL) */
  Table *pTriggerTab;  /* Table triggers are being coded for */
  u32 oldmask;         /* Mask of old.* columns referenced */
  u8 eTriggerOp;       /* TK_UPDATE, TK_INSERT or TK_DELETE */
  u8 eOrconf;          /* Default ON CONFLICT policy for trigger steps */
  u8 disableTriggers;  /* True to disable triggers */

  /* Above is constant between recursions.  Below is reset before and after
  ** each recursion */

  int nVar;            /* Number of '?' variables seen in the SQL so far */
  int nVarExpr;        /* Number of used slots in apVarExpr[] */
  int nVarExprAlloc;   /* Number of allocated slots in apVarExpr[] */

** key functionality is available. If OMIT_TRIGGER is defined but
** OMIT_FOREIGN_KEY is not, only some of the functions are no-oped. In
** this case foreign keys are parsed, but no other functionality is 
** provided (enforcement of FK constraints requires the triggers sub-system).
*/
#if !defined(SQLITE_OMIT_FOREIGN_KEY) && !defined(SQLITE_OMIT_TRIGGER)
  void sqlite3FkCheck(Parse*, Table*, ExprList*, int, int);
  void sqlite3FkDropTable(Parse*, SrcList *, Table*);
  void sqlite3FkActions(Parse*, Table*, ExprList*, int);
  int sqlite3FkRequired(Parse*, Table*, ExprList*);
  u32 sqlite3FkOldmask(Parse*, Table*, ExprList*);
  FKey *sqlite3FkReferences(Table *);
#else
  #define sqlite3FkActions(a,b,c,d)
  #define sqlite3FkCheck(a,b,c,d,e)
  #define sqlite3FkDropTable(a,b,c)
  #define sqlite3FkOldmask(a,b,c)  0
  #define sqlite3FkRequired(a,b,c) 0
#endif
#ifndef SQLITE_OMIT_FOREIGN_KEY
  void sqlite3FkDelete(Table*);
#else
  #define sqlite3FkDelete(a)
#endif

** To state it another way:  This routine returns a list of all triggers
** that fire off of pTab.  The list will include any TEMP triggers on
** pTab as well as the triggers lised in pTab->pTrigger.
*/
Trigger *sqlite3TriggerList(Parse *pParse, Table *pTab){
  Schema * const pTmpSchema = pParse->db->aDb[1].pSchema;
  Trigger *pList = 0;                  /* List of triggers to return */

  if( pParse->disableTriggers ){
    return 0;
  }

  if( pTmpSchema!=pTab->pSchema ){
    HashElem *p;
    for(p=sqliteHashFirst(&pTmpSchema->trigHash); p; p=sqliteHashNext(p)){
      Trigger *pTrig = (Trigger *)sqliteHashData(p);
      if( pTrig->pTabSchema==pTab->pSchema
       && 0==sqlite3StrICmp(pTrig->table, pTab->zName) 

# fkey2-genfkey.*: Tests that were used with the shell tool .genfkey
#            command. Recycled to test the built-in implementation.
#


proc drop_all_tables {{db db}} {
  set tbls [execsql {SELECT name FROM sqlite_master WHERE type = 'table'}]
  execsql { PRAGMA foreign_keys = OFF }
  foreach t [execsql {
    SELECT name FROM sqlite_master 
    WHERE type = 'table' AND name NOT like 'sqlite_%'
  }] {
    execsql "DROP TABLE $t"
  }
  execsql { PRAGMA foreign_keys = ON }
}

execsql { PRAGMA foreign_keys = on }

if 0 {
execsql {
  CREATE TABLE t1(a PRIMARY KEY, b REFERENCES t1);

} {1 {foreign key constraint failed}}

do_test fkey3-1.3 {
  catchsql {
    DROP TABLE t1;
  }
} {1 {foreign key constraint failed}}

do_test fkey3-1.4 {
  execsql {
    DROP TABLE t2;
  }
} {}

do_test fkey3-1.5 {
  execsql {
    DROP TABLE t1;
  }
} {}

do_test fkey3-2.1 {
  execsql {
    PRAGMA foreign_keys=ON;
    CREATE TABLE t1(x INTEGER PRIMARY KEY);
    INSERT INTO t1 VALUES(100);
    INSERT INTO t1 VALUES(101);
    CREATE TABLE t2(y INTEGER PRIMARY KEY REFERENCES t1 (x) ON UPDATE SET NULL);
  }
  execsql {
    INSERT INTO t2 VALUES(100);
    INSERT INTO t2 VALUES(101);
    SELECT 1, x FROM t1;
    SELECT 2, y FROM t2;
  }
} {1 100 1 101 2 100 2 101}

finish_test