From 788536b16580154cb4f021275a3d8e8376dbd2b2 Mon Sep 17 00:00:00 2001
From: drh <drh@noemail.net>
Date: Wed, 23 Sep 2009 03:01:58 +0000
Subject: [PATCH] Do not run ON UPDATE actions of a foreign key constraint
 unless at least one column value really does change.

FossilOrigin-Name: 71ac8e28e55ff0250ebe2fe239159ce2458d9165
---
 manifest      | 18 +++++++++---------
 manifest.uuid |  2 +-
 src/fkey.c    | 30 ++++++++++++++++++++++++++++--
 3 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/manifest b/manifest
index 212cfdf42e..6d7e25235b 100644
--- a/manifest
+++ b/manifest
@@ -1,8 +1,8 @@
 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA1
 
-C Generalize\sthe\sIS\sand\sIS\sNOT\soperators\sso\sthat\stheir\sright-hand\sside\scan\sbe\nan\sarbitrary\sexpression\sand\snot\ssimple\sthe\sconstant\sNULL.\s\sThey\swork\slike\n=\sand\s<>\sexcept\sthat\sNULL\svalues\scompare\sequal\sto\sone\sanother\san\sunequal\sto\neverything\selse.
-D 2009-09-23T02:29:37
+C Do\snot\srun\sON\sUPDATE\sactions\sof\sa\sforeign\skey\sconstraint\sunless\sat\sleast\sone\ncolumn\svalue\sreally\sdoes\schange.
+D 2009-09-23T03:01:59
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in 4ca3f1dd6efa2075bcb27f4dc43eef749877740d
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -119,7 +119,7 @@ F src/date.c 657ff12ca0f1195b531561afacbb38b772d16638
 F src/delete.c 15499f5d10047d38e68ce991b3f88cbddb6e0931
 F src/expr.c 8a663240f374a5326ee157df3d27751f58b7676a
 F src/fault.c dc88c821842157460750d2d61a8a8b4197d047ff
-F src/fkey.c fa1ad144926a8536e23cbbf64c0e51b8f2fdd4bf
+F src/fkey.c de296942345984960792f12ea4236a6bef2f800b
 F src/func.c e536218d193b8d326aab91120bc4c6f28aa2b606
 F src/global.c 271952d199a8cc59d4ce840b3bbbfd2f30c8ba32
 F src/hash.c ebcaa921ffd9d86f7ea5ae16a0a29d1c871130a7
@@ -756,14 +756,14 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
-P 3fc938c961fd7810594224b91a2d6e1ac9e48084
-R d99ab25244fa05bd56d10d71bb3bee44
+P 98853f6104076c50ea92175e17a3254bfbbd4619
+R 827ec94cc2eb4c57959ec45f4b3d8098
 U drh
-Z 4608482892179163853473e1fbf42a31
+Z ec752338f3000365feb24aa823e5d734
 -----BEGIN PGP SIGNATURE-----
 Version: GnuPG v1.4.6 (GNU/Linux)
 
-iD8DBQFKuYgUoxKgR168RlERApeHAJ48L4oeCXw8ZV6ov3G5+bjNMfQIewCfX/Rc
-qXj8iamFDJ6JXwF0VP/iAOI=
-=lSDQ
+iD8DBQFKuY+roxKgR168RlERAq1TAKCDsc87lQ7RxW/6hlefk/rm32wxUACdGuQz
+1VFw5lE97EA4c5Tiy8ftXks=
+=0G/k
 -----END PGP SIGNATURE-----
diff --git a/manifest.uuid b/manifest.uuid
index 82c45ac0f3..3c61b0a6f3 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-98853f6104076c50ea92175e17a3254bfbbd4619
\ No newline at end of file
+71ac8e28e55ff0250ebe2fe239159ce2458d9165
\ No newline at end of file
diff --git a/src/fkey.c b/src/fkey.c
index 32aef9bbe0..1e64310ead 100644
--- a/src/fkey.c
+++ b/src/fkey.c
@@ -395,6 +395,7 @@ static void fkTriggerDelete(sqlite3 *dbMem, Trigger *p){
     TriggerStep *pStep = p->step_list;
     sqlite3ExprDelete(dbMem, pStep->pWhere);
     sqlite3ExprListDelete(dbMem, pStep->pExprList);
+    sqlite3ExprDelete(dbMem, p->pWhen);
     sqlite3DbFree(dbMem, p);
   }
 }
@@ -649,6 +650,7 @@ static Trigger *fkActionTrigger(
     Expr *pWhere = 0;             /* WHERE clause of trigger step */
     ExprList *pList = 0;          /* Changes list if ON UPDATE CASCADE */
     int i;                        /* Iterator variable */
+    Expr *pWhen = 0;              /* WHEN clause for the trigger */
 
     if( locateFkeyIndex(pParse, pTab, pFKey, &pIdx, &aiCol) ) return 0;
     assert( aiCol || pFKey->nCol==1 );
@@ -678,6 +680,25 @@ static Trigger *fkActionTrigger(
       , 0);
       pWhere = sqlite3ExprAnd(db, pWhere, pEq);
 
+      /* For ON UPDATE, construct the next term of the WHEN clause.
+      ** The final WHEN clause will be like this:
+      **
+      **    WHEN NOT(old.col1 IS new.col1 AND ... AND old.colN IS new.colN)
+      */
+      if( pChanges ){
+        pEq = sqlite3PExpr(pParse, TK_IS,
+            sqlite3PExpr(pParse, TK_DOT, 
+              sqlite3PExpr(pParse, TK_ID, 0, 0, &tOld),
+              sqlite3PExpr(pParse, TK_ID, 0, 0, &tToCol),
+              0),
+            sqlite3PExpr(pParse, TK_DOT, 
+              sqlite3PExpr(pParse, TK_ID, 0, 0, &tNew),
+              sqlite3PExpr(pParse, TK_ID, 0, 0, &tToCol),
+              0),
+            0);
+        pWhen = sqlite3ExprAnd(db, pWhen, pEq);
+      }
+  
       if( action!=OE_Cascade || pChanges ){
         Expr *pNew;
         if( action==OE_Cascade ){
@@ -724,13 +745,18 @@ static Trigger *fkActionTrigger(
   
       pStep->pWhere = sqlite3ExprDup(db, pWhere, EXPRDUP_REDUCE);
       pStep->pExprList = sqlite3ExprListDup(db, pList, EXPRDUP_REDUCE);
+      if( pWhen ){
+        pWhen = sqlite3PExpr(pParse, TK_NOT, pWhen, 0, 0);
+        pTrigger->pWhen = sqlite3ExprDup(db, pWhen, EXPRDUP_REDUCE);
+      }
     }
 
     /* Re-enable the lookaside buffer, if it was disabled earlier. */
     db->lookaside.bEnabled = enableLookaside;
 
-    sqlite3ExprDelete(pParse->db, pWhere);
-    sqlite3ExprListDelete(pParse->db, pList);
+    sqlite3ExprDelete(db, pWhere);
+    sqlite3ExprDelete(db, pWhen);
+    sqlite3ExprListDelete(db, pList);
     if( db->mallocFailed==1 ){
       fkTriggerDelete(db, pTrigger);
       return 0;