diff --git a/manifest b/manifest
index 6f4efd9bdc..55819af278 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Experimental\soptimization\sto\srewrite\sa\sSELECT\swith\san\sEXISTS(...)\sexpression\sin\sthe\sWHERE\sclause\sas\sa\sjoin.
-D 2024-06-07T21:00:42.970
+C Add\sextra\stests\sfor\sthe\schanges\son\sthis\sbranch.
+D 2024-06-08T18:13:12.691
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -755,7 +755,7 @@ F src/printf.c 8b250972305e14b365561be5117ed0fd364e4fd58968776df1ce64c6280b90f9
 F src/random.c 606b00941a1d7dd09c381d3279a058d771f406c5213c9932bbd93d5587be4b9c
 F src/resolve.c 9c7786f032dea81487e7d94cb17849936f0e9b8891bfc91a6ac24ab193762804
 F src/rowset.c 8432130e6c344b3401a8874c3cb49fefe6873fec593294de077afea2dce5ec97
-F src/select.c 669cfc0392c8a0bd43e5a199cba5f796aead3423e2c529d09148adfa57ae1152
+F src/select.c 06146768a11bfe8928fea0aabf8addedd4d146a8c4be70558f5c8ecdcc2ce338
 F src/shell.c.in 77d12a0dab8724819e64a14d5fbaad91a934be2b22ad329708fba9ba78993f04
 F src/sqlite.h.in cbd3e4177791a61c056fd81e37a5b21bb6c8cb2ea8cac558c625974673f50acf
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
@@ -1114,7 +1114,8 @@ F test/exclusive.test 7ff63be7503990921838d5c9f77f6e33e68e48ed1a9d48cd28745bf650
 F test/exclusive2.test 984090e8e9d1b331d2e8111daf6e5d61dda0bef7
 F test/exec.test e949714dc127eaa5ecc7d723efec1ec27118fdd7
 F test/exists.test 79a75323c78f02bbe9c251ea502a092f9ef63dac
-F test/existsexpr.test a86e8300a2e0cd26109ba5b0d552dbc598b9ad4b79dfd26cac255839c9d5cf6a
+F test/existsexpr.test b101143b177d623c35166589d3e6772021dfe4f625ac318c91726a998939cd19
+F test/existsfault.test ff41c11f3052c1bbd4f8dd557802310026253d67d7c4e3a180c16d2f0862973e
 F test/expr.test 5c06696478212e5a04e04b043f993373f6f8e5ce5a80f5548a84703b123b6caa
 F test/expr2.test c27327ae9c017a7ff6280123f67aff496f912da74d78c888926d68b46ec75fd8
 F test/exprfault.test da33606d799718e2f8e34efd0e5858884a1ad87f608774c552a7f5517cc27181
@@ -2196,11 +2197,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P c4a9dda2809c6e0e3d928e11e5553ead82cd9df551bcd35b11a7d869ef80ab8e
-R 7e4221204288c4c4593aaccf38fb6e40
-T *branch * exists-to-join
-T *sym-exists-to-join *
-T -sym-trunk *
+P 972a33db0b0e924b78d5309d222d8ea298bd59c72da14ea2d14e8e2caaad1e0a
+R 20ea5e8daae9a69a6e09a05cc19a6a37
 U dan
-Z 8ebacdbf5bd3ee682966a7aab4962dc0
+Z cbb8e2989ade033c119abad0907d9ec3
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index 7a08d86957..ce5b16061c 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-972a33db0b0e924b78d5309d222d8ea298bd59c72da14ea2d14e8e2caaad1e0a
\ No newline at end of file
+a6365c778f2a6d6fa78e8520553373898f382ce73bf6496533e26291648ef5d1
\ No newline at end of file
diff --git a/src/select.c b/src/select.c
index 332fba3b85..f21559e8da 100644
--- a/src/select.c
+++ b/src/select.c
@@ -7382,12 +7382,13 @@ static u64 findConstIdxTerms(
 **      WHERE S.sid = R.sid AND R.day = '2022-10-25';
 */
 static void existsToJoin(Parse *pParse, Select *p, Expr *pWhere){
-  if( pWhere && p->pSrc->nSrc>0 ){
+  if( pWhere && p->pSrc->nSrc>0 && pParse->db->mallocFailed==0 ){
     if( pWhere->op==TK_AND ){
+      Expr *pRight = pWhere->pRight;
       existsToJoin(pParse, p, pWhere->pLeft);
-      existsToJoin(pParse, p, pWhere->pRight);
+      existsToJoin(pParse, p, pRight);
     }
-    else if( pWhere->op==TK_EXISTS && (pWhere->flags & EP_xIsSelect) ){
+    else if( pWhere->op==TK_EXISTS ){
       Select *pSub = pWhere->x.pSelect;
       if( pSub->pSrc->nSrc==1 
        && (pSub->selFlags & (SF_Aggregate|SF_Correlated))==SF_Correlated
@@ -7401,28 +7402,26 @@ static void existsToJoin(Parse *pParse, Select *p, Expr *pWhere){
           bTransform = 1;
         }
         for(pIdx=pTab->pIndex; pIdx && bTransform==0; pIdx=pIdx->pNext){
-          if( pIdx->onError && pIdx->nKeyCol<64 ){
+          if( pIdx->onError && pIdx->nKeyCol<=63 ){
             u64 c = findConstIdxTerms(pParse, iCsr, pIdx, pSub->pWhere);
-            if( c==(1 << pIdx->nKeyCol)-1 ){
+            if( c==((u64)1 << pIdx->nKeyCol)-1 ){
               bTransform = 1;
             }
           }
         }
         if( bTransform ){
-          p->pSrc = sqlite3SrcListAppendList(pParse, p->pSrc, pSub->pSrc);
-          pSub->pSrc = 0;
-          if( p->pWhere ){
-            p->pWhere = sqlite3PExpr(pParse, TK_AND, p->pWhere, pSub->pWhere);
-          }else{
-            p->pWhere = pSub->pWhere;
-          }
-          pSub->pWhere = 0;
-
-          sqlite3SelectDelete(pParse->db, pSub);
           memset(pWhere, 0, sizeof(*pWhere));
           pWhere->op = TK_INTEGER;
           pWhere->u.iValue = 1;
           ExprSetProperty(pWhere, EP_IntValue);
+
+          assert( p->pWhere!=0 );
+          p->pSrc = sqlite3SrcListAppendList(pParse, p->pSrc, pSub->pSrc);
+          p->pWhere = sqlite3PExpr(pParse, TK_AND, p->pWhere, pSub->pWhere);
+
+          pSub->pWhere = 0;
+          pSub->pSrc = 0;
+          sqlite3SelectDelete(pParse->db, pSub);
         }
       }
     }
diff --git a/test/existsexpr.test b/test/existsexpr.test
index 4bd55db52d..344f8cff6e 100644
--- a/test/existsexpr.test
+++ b/test/existsexpr.test
@@ -17,9 +17,8 @@ set testprefix existsexpr
 
 
 do_execsql_test 1.0 {
-  CREATE TABLE x1(a, b);
+  CREATE TABLE x1(a, b, PRIMARY KEY(a)) WITHOUT ROWID;
   INSERT INTO x1 VALUES(1, 2), (3, 4), (5, 6);
-  CREATE UNIQUE INDEX x1a ON x1(a);
   CREATE INDEX x1b ON x1(b);
 
   CREATE TABLE x2(x, y);
@@ -111,6 +110,261 @@ do_execsql_test 2.5.1 {
   SELECT count(*) FROM t1 WHERE EXISTS (SELECT 1 FROM t2 WHERE t2.rowid=a);
 } {~/SUBQUERY/}
 
+#-------------------------------------------------------------------------
+proc do_subquery_test {tn bSub sql res} {
+  set r1(0) ~/SUBQUERY/
+  set r1(1) /SUBQUERY/
+  do_execsql_test $tn.1 "explain query plan $sql" $r1($bSub)
+  do_execsql_test $tn.2 $sql $res
+}
+
+do_execsql_test 3.0 {
+  CREATE TABLE y1(a, b, c);
+  CREATE TABLE y2(x, y, z);
+  CREATE UNIQUE INDEX y2zy ON y2(z, y);
+
+  INSERT INTO y1 VALUES(1, 1, 1);
+  INSERT INTO y1 VALUES(2, 2, 2);
+  INSERT INTO y1 VALUES(3, 3, 3);
+  INSERT INTO y1 VALUES(4, 4, 4);
+
+  INSERT INTO y2 VALUES(1, 1, 1);
+  INSERT INTO y2 VALUES(3, 3, 3);
+}
+
+do_subquery_test 3.1 0 {
+  SELECT * FROM y1 WHERE EXISTS ( 
+      SELECT 1 FROM y2 WHERE z=a AND y=b AND x=z
+  )
+} {
+  1 1 1          3 3 3
+}    
+
+do_subquery_test 3.2 0 {
+  SELECT * FROM y1 WHERE EXISTS ( 
+      SELECT 1 FROM y2 WHERE z=max(a,b) AND y=min(b,a) AND x=z
+  )
+} {
+  1 1 1          3 3 3
+}    
+
+do_subquery_test 3.3 0 {
+  SELECT * FROM y1 WHERE EXISTS ( 
+      SELECT 1 FROM y2 WHERE z=max(a,b) AND y=min(b,a) AND c!=3
+  )
+} {
+  1 1 1
+}    
+
+do_subquery_test 3.4 1 {
+  SELECT * FROM y1 WHERE EXISTS ( 
+      SELECT 1 FROM y2 WHERE z=max(a,b) AND b=3
+  )
+} {
+  3 3 3
+}    
+
+do_subquery_test 3.5 0 {
+  SELECT * FROM y1 WHERE EXISTS ( 
+      SELECT 1 FROM y2 WHERE z=a-1 AND y=a-1
+  )
+} {
+  2 2 2
+  4 4 4
+}    
+
+do_subquery_test 3.6 1 {
+  SELECT * FROM y1 WHERE EXISTS ( 
+      SELECT 1 FROM y2 WHERE z=a-1 AND y+1=a
+  )
+} {
+  2 2 2
+  4 4 4
+}    
+
+do_subquery_test 3.7 1 {
+  SELECT * FROM y1 WHERE EXISTS ( 
+      SELECT count(*) FROM y2 WHERE z=a-1 AND y=a-1
+  )
+} {
+  1 1 1
+  2 2 2
+  3 3 3
+  4 4 4
+}    
+
+do_subquery_test 3.8 1 {
+  SELECT * FROM y1 WHERE EXISTS ( SELECT a+1 FROM y2 )
+} {
+  1 1 1
+  2 2 2
+  3 3 3
+  4 4 4
+}    
+
+do_subquery_test 3.9 1 {
+  SELECT * FROM y1 WHERE EXISTS ( 
+      SELECT 1 FROM y2 one, y2 two WHERE one.z=a-1 AND one.y=a-1
+  )
+} {
+  2 2 2
+  4 4 4
+}    
+
+#-------------------------------------------------------------------------
+reset_db
+do_execsql_test 4.0 {
+  CREATE TABLE tx1(a TEXT COLLATE nocase, b TEXT);
+  CREATE UNIQUE INDEX tx1ab ON tx1(a, b);
+
+  INSERT INTO tx1 VALUES('a', 'a');
+  INSERT INTO tx1 VALUES('B', 'b');
+  INSERT INTO tx1 VALUES('c', 'c');
+  INSERT INTO tx1 VALUES('D', 'd');
+  INSERT INTO tx1 VALUES('e', 'e');
+
+  CREATE TABLE tx2(x, y);
+  INSERT INTO tx2 VALUES('A', 'a');
+  INSERT INTO tx2 VALUES('b', 'b');
+  INSERT INTO tx2 VALUES('C', 'c');
+  INSERT INTO tx2 VALUES('D', 'd');
+}
+
+do_subquery_test 4.1 0 {
+  SELECT * FROM tx2 WHERE EXISTS (
+    SELECT 1 FROM tx1 WHERE a=x AND b=y
+  )
+} {
+  A a
+  b b
+  C c
+  D d
+}
+
+do_subquery_test 4.2 1 {
+  SELECT * FROM tx2 WHERE EXISTS (
+    SELECT 1 FROM tx1 WHERE a=x AND b=y COLLATE nocase
+  )
+} {
+  A a
+  b b
+  C c
+  D d
+}
+
+do_execsql_test 4.3 {
+  DROP INDEX tx1ab;
+  CREATE UNIQUE INDEX tx1ab ON tx1(a COLLATE binary, b);
+}
+
+do_subquery_test 4.4 1 {
+  SELECT * FROM tx2 WHERE EXISTS (
+    SELECT 1 FROM tx1 WHERE a=x AND b=y
+  )
+} {
+  A a
+  b b
+  C c
+  D d
+}
+
+do_subquery_test 4.4 0 {
+  SELECT * FROM tx2 WHERE EXISTS (
+    SELECT 1 FROM tx1 WHERE a=x COLLATE binary AND b=y
+  )
+} {
+  D d
+}
+
+do_subquery_test 4.4 1 {
+  SELECT EXISTS ( SELECT x FROM tx1 ) FROM tx2
+} {
+  1 1 1 1
+}
+
+do_subquery_test 4.4 1 {
+  SELECT (SELECT EXISTS ( SELECT x FROM tx1 ) WHERE 1) FROM tx2
+} {
+  1 1 1 1
+}
+
+#-------------------------------------------------------------------------
+proc cols {s f} {
+  set lCols [list]
+  for {set i $s} {$i<=$f} {incr i} {
+    lappend lCols [format "c%02d" $i]
+  }
+  join $lCols ", "
+}
+proc vals {n val} {
+  set lVal [list]
+  for {set i 0} {$i<$n} {incr i} {
+    lappend lVal $val
+  }
+  join $lVal ", "
+}
+proc exprs {s f} {
+  set lExpr [list]
+  for {set i $s} {$i<=$f} {incr i} {
+    lappend lExpr [format "c%02d = o" $i]
+  }
+  join $lExpr " AND "
+}
+
+
+do_execsql_test 5.0 "
+  CREATE TABLE a1( [cols 0 99] );
+"
+do_execsql_test 5.1 "
+  -- 63 column index
+  CREATE UNIQUE INDEX a1idx1 ON a1( [cols 0 62] );
+"
+do_execsql_test 5.2 "
+  -- 64 column index
+  CREATE UNIQUE INDEX a1idx2 ON a1( [cols 10 73] );
+"
+do_execsql_test 5.2 "
+  -- 65 column index
+  CREATE UNIQUE INDEX a1idx3 ON a1( [cols 20 84] );
+"
+
+do_test 5.3 {
+  foreach v {1 2 3 4 5 6} {
+    execsql "INSERT INTO a1 VALUES( [vals 100 $v] )"
+  }
+} {}
+
+do_execsql_test 5.4 {
+  CREATE TABLE a2(o);
+  INSERT INTO a2 VALUES(2), (5); 
+}
+
+do_subquery_test 5.5 0 "
+  SELECT o FROM a2 WHERE EXISTS (
+    SELECT 1 FROM a1 WHERE [exprs 0 62]
+  )
+" {
+  2 5
+}
+
+do_subquery_test 5.6 1 "
+  SELECT o FROM a2 WHERE EXISTS (
+    SELECT 1 FROM a1 WHERE [exprs 10 73]
+  )
+" {
+  2 5
+}
+
+do_subquery_test 5.7 1 "
+  SELECT o FROM a2 WHERE EXISTS (
+    SELECT 1 FROM a1 WHERE [exprs 20 84]
+  )
+" {
+  2 5
+}
+
+
+
 finish_test
 
 
diff --git a/test/existsfault.test b/test/existsfault.test
new file mode 100644
index 0000000000..4b335d84cd
--- /dev/null
+++ b/test/existsfault.test
@@ -0,0 +1,49 @@
+# 2024 May 25
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+source $testdir/lock_common.tcl
+source $testdir/malloc_common.tcl
+set testprefix existsfault
+
+db close
+sqlite3_shutdown
+sqlite3_config_lookaside 0 0
+sqlite3_initialize
+autoinstall_test_functions
+sqlite3 db test.db
+
+do_execsql_test 1.0 {
+  CREATE TABLE x1(a, b);
+  INSERT INTO x1 VALUES(1, 2), (3, 4), (5, 6);
+  CREATE UNIQUE INDEX x1a ON x1(a);
+  CREATE INDEX x1b ON x1(b);
+
+  CREATE TABLE x2(x, y);
+  INSERT INTO x2 VALUES(1, 2), (3, 4), (5, 6);
+}
+
+do_faultsim_test 1 -faults oom* -prep {
+  sqlite3 db test.db
+  execsql { SELECT * FROM sqlite_schema }
+} -body {
+  execsql {
+    SELECT count(*) FROM x2 WHERE EXISTS (SELECT 1 FROM x1 WHERE a=x) AND y!=11
+  }
+} -test {
+  faultsim_test_result {0 3}
+}
+
+finish_test
+
+