If a RETURNING clause contains a subquery that references the table that is

being updated in the statement that includes the RETURNING clause, then mark
the subquery as correlated sot hat it is recomputed for each result and not
just computed once and reused.  See
[forum:/forumpost/2c83569ce8945d39|forum post 2c83569ce8945d39].

Author: D. Richard Hipp

src/trigger.c

@@ -951,6 +951,72 @@ static ExprList *sqlite3ExpandReturning(
   return pNew;
 }
 
+/* If the Expr node is a subquery or an EXISTS operator or an IN operator that
+** uses a subquery, and if the subquery is SF_Correlated, then mark the
+** expression as EP_VarSelect.
+*/
+static int sqlite3ReturningSubqueryVarSelect(Walker *NotUsed, Expr *pExpr){
+  UNUSED_PARAMETER(NotUsed);
+  if( ExprUseXSelect(pExpr)
+   && (pExpr->x.pSelect->selFlags & SF_Correlated)!=0
+  ){
+    testcase( ExprHasProperty(pExpr, EP_VarSelect) );
+    ExprSetProperty(pExpr, EP_VarSelect);
+  }
+  return WRC_Continue;
+}
+
+
+/*
+** If the SELECT references the table pWalker->u.pTab, then do two things:
+**
+**    (1) Mark the SELECT as as SF_Correlated.
+**    (2) Set pWalker->eCode to non-zero so that the caller will know
+**        that (1) has happened.
+*/
+static int sqlite3ReturningSubqueryCorrelated(Walker *pWalker, Select *pSelect){
+  int i;
+  SrcList *pSrc;
+  assert( pSelect!=0 );
+  pSrc = pSelect->pSrc;
+  assert( pSrc!=0 );
+  for(i=0; i<pSrc->nSrc; i++){
+    if( pSrc->a[i].pTab==pWalker->u.pTab ){
+      testcase( pSelect->selFlags & SF_Correlated );
+      pSelect->selFlags |= SF_Correlated;
+      pWalker->eCode = 1;
+      break;
+    }
+  }
+  return WRC_Continue;
+}
+
+/*
+** Scan the expression list that is the argument to RETURNING looking
+** for subqueries that depend on the table which is being modified in the
+** statement that is hosting the RETURNING clause (pTab).  Mark all such
+** subqueries as SF_Correlated.  If the subqueries are part of an
+** expression, mark the expression as EP_VarSelect.
+**
+** https://sqlite.org/forum/forumpost/2c83569ce8945d39
+*/
+static void sqlite3ProcessReturningSubqueries(
+  ExprList *pEList,
+  Table *pTab
+){
+  Walker w;
+  memset(&w, 0, sizeof(w));
+  w.xExprCallback = sqlite3ExprWalkNoop;
+  w.xSelectCallback = sqlite3ReturningSubqueryCorrelated;
+  w.u.pTab = pTab;
+  sqlite3WalkExprList(&w, pEList);
+  if( w.eCode ){
+    w.xExprCallback = sqlite3ReturningSubqueryVarSelect;
+    w.xSelectCallback = sqlite3SelectWalkNoop;
+    sqlite3WalkExprList(&w, pEList);
+  }
+}
+
 /*
 ** Generate code for the RETURNING trigger.  Unlike other triggers
 ** that invoke a subprogram in the bytecode, the code for RETURNING
@@ -1014,6 +1080,7 @@ static void codeReturningTrigger(
       int i;
       int nCol = pNew->nExpr;
       int reg = pParse->nMem+1;
+      sqlite3ProcessReturningSubqueries(pNew, pTab);
       pParse->nMem += nCol+2;
       pReturning->iRetReg = reg;
       for(i=0; i<nCol; i++){

test/returning1.test

@@ -460,4 +460,64 @@ do_catchsql_test 19.1 {
   END;
 } {0 {}}
 
+# 2024-04-24
+# https://sqlite.org/forum/forumpost/2c83569ce8945d39
+#
+# If the RETURNING clause includes subqueries that reference the
+# table being modified, make sure that the subqueries are identified
+# as correlated so that the results are recomputed after each step
+# instead of being computed once and reused.
+#
+reset_db
+db null N
+do_execsql_test 20.1 {
+  CREATE TABLE t1(a INTEGER PRIMARY KEY, b INT);
+  INSERT INTO t1 VALUES(1,10),(2,20),(3,30),(4,40),(6,60),(8,80);
+  BEGIN;
+  DELETE FROM t1 WHERE a<>3
+    RETURNING a,
+              (SELECT min(a) FROM t1),
+              (SELECT max(a) FROM t1),
+              (SELECT round(avg(a),2) FROM t1);
+  ROLLBACK;
+} {
+  1 2 8 4.6
+  2 3 8 5.25
+  4 3 8 5.67
+  6 3 8 5.5
+  8 3 3 3.0
+}
+do_execsql_test 20.2 {
+  BEGIN;
+  DELETE FROM t1
+    RETURNING a,
+              (SELECT min(a) FROM t1),
+              (SELECT max(a) FROM t1),
+              (SELECT round(avg(a),2) FROM t1);
+  ROLLBACK;
+} {
+  1 2 8 4.6
+  2 3 8 5.25
+  3 4 8 6.0
+  4 6 8 7.0
+  6 8 8 8.0
+  8 N N N
+}
+do_execsql_test 20.3 {
+  BEGIN;
+  DELETE FROM t1
+    RETURNING a,
+              (SELECT min(t2.a)+t1.a*100 FROM t1 AS t2),
+              (SELECT max(t2.a)+t1.a*100 FROM t1 AS t2),
+              (SELECT round(avg(t2.a),2)+t1.a*100 FROM t1 AS t2);
+  ROLLBACK;
+} {
+  1 102 108 104.6
+  2 203 208 205.25
+  3 304 308 306.0
+  4 406 408 407.0
+  6 608 608 608.0
+  8 N N N
+}
+
 finish_test