Refactor the SrcItem object so that information about subqueries is stored

in a separately allocated Subquery object.  This reduces the memory requirements
for SrcItem and makes the code run faster.  It also provides an expansion path
for subquery processing that does not burden simple queries.  The current
checking mostly works, but there are still issues that need to be tracked
down and fixed.

FossilOrigin-Name: 8ff5dda8448d7e1a533d7f27db2573ce68fa9956b9d9847ced45e83c1f06bab0

1 files changed, 84 insertions, 12 deletions

diff --git a/src/build.c b/src/build.c
index ff798087a..b585c1971 100644
--- a/src/build.c
+++ b/src/build.c
@@ -4914,14 +4914,41 @@ void sqlite3SrcListAssignCursors(Parse *pParse, SrcList *pList){
     for(i=0, pItem=pList->a; i<pList->nSrc; i++, pItem++){
       if( pItem->iCursor>=0 ) continue;
       pItem->iCursor = pParse->nTab++;
-      if( pItem->sq.pSelect ){
-        sqlite3SrcListAssignCursors(pParse, pItem->sq.pSelect->pSrc);
+      if( pItem->fg.isSubquery ){
+        assert( pItem->u4.pSubq!=0 );
+        assert( pItem->u4.pSubq->pSelect!=0 );
+        assert( pItem->u4.pSubq->pSelect->pSrc!=0 );
+        sqlite3SrcListAssignCursors(pParse, pItem->u4.pSubq->pSelect->pSrc);
       }
     }
   }
 }
 
 /*
+** Delete a Subquery object and its substructure.
+*/
+void sqlite3SubqueryDelete(sqlite3 *db, Subquery *pSubq){
+  assert( pSubq!=0 && pSubq->pSelect!=0 );
+  sqlite3SelectDelete(db, pSubq->pSelect);
+  sqlite3DbFree(db, pSubq);
+}
+
+/*
+** Remove a Subquery from a SrcItem.  Return the associated Select object.
+** The returned Select becomes the responsibility of the caller.
+*/
+Select *sqlite3SubqueryDetach(sqlite3 *db, SrcItem *pItem){
+  Select *pSel;
+  assert( pItem!=0 );
+  assert( pItem->fg.isSubquery );
+  pSel = pItem->u4.pSubq->pSelect;
+  sqlite3DbFree(db, pItem->u4.pSubq);
+  pItem->u4.pSubq = 0;
+  pItem->fg.isSubquery = 0;
+  return pSel;
+}
+
+/*
 ** Delete an entire SrcList including all its substructure.
 */
 void sqlite3SrcListDelete(sqlite3 *db, SrcList *pList){
@@ -4932,22 +4959,19 @@ void sqlite3SrcListDelete(sqlite3 *db, SrcList *pList){
   for(pItem=pList->a, i=0; i<pList->nSrc; i++, pItem++){
  
     /* Check invariants on SrcItem */
-    assert( pItem->sq.pSelect==0
-         || (pItem->sq.pSelect->selFlags & SF_MultiValue)==0
-         || (pItem->fg.hadSchema==0
-              && (pItem->fg.fixedSchema || pItem->u4.zDatabase==0)) );
+    assert( !pItem->fg.hadSchema || !pItem->fg.isSubquery );
     assert( pItem->fg.hadSchema==0 || pItem->fg.fixedSchema==1 );
 
-
     if( pItem->zName ) sqlite3DbNNFreeNN(db, pItem->zName);
     if( pItem->zAlias ) sqlite3DbNNFreeNN(db, pItem->zAlias);
-    if( pItem->fg.fixedSchema==0 && pItem->u4.zDatabase!=0 ){
+    if( pItem->fg.isSubquery ){
+      sqlite3SubqueryDelete(db, pItem->u4.pSubq);
+    }else if( pItem->fg.fixedSchema==0 && pItem->u4.zDatabase!=0 ){
       sqlite3DbNNFreeNN(db, pItem->u4.zDatabase);
     }
     if( pItem->fg.isIndexedBy ) sqlite3DbFree(db, pItem->u1.zIndexedBy);
     if( pItem->fg.isTabFunc ) sqlite3ExprListDelete(db, pItem->u1.pFuncArg);
     sqlite3DeleteTable(db, pItem->pSTab);
-    if( pItem->sq.pSelect ) sqlite3SelectDelete(db, pItem->sq.pSelect);
     if( pItem->fg.isUsing ){
       sqlite3IdListDelete(db, pItem->u3.pUsing);
     }else if( pItem->u3.pOn ){
@@ -4958,6 +4982,52 @@ void sqlite3SrcListDelete(sqlite3 *db, SrcList *pList){
 }
 
 /*
+** Attach a Subquery object to pItem->uv.pSubq.  Set the
+** pSelect value but leave all the other values initialized
+** to zero.
+**
+** A copy of the Select object is made if dupSelect is true, and the
+** SrcItem takes responsibility for deleting the copy.  If dupSelect is
+** false, ownership of the Select passes to the SrcItem.  Either way,
+** the SrcItem will take responsibility for deleting the Select.
+**
+** When dupSelect is zero, that means the Select might get deleted right
+** away if there is an OOM error.  Beware.
+**
+** Return non-zero on success.  Return zero on an OOM error.
+*/
+int sqlite3SrcItemAttachSubquery(
+  Parse *pParse,     /* Parsing context */
+  SrcItem *pItem,    /* Item to which the subquery is to be attached */
+  Select *pSelect,   /* The subquery SELECT.  Must be non-NULL */
+  int dupSelect      /* If true, attach a copy of pSelect, not pSelect itself.*/
+){
+  Subquery *p;
+  if( pSelect==0 ) return SQLITE_OK;
+  assert( pItem->fg.isSubquery==0 );
+  if( pItem->fg.fixedSchema==0 && pItem->u4.zDatabase!=0 ){
+    sqlite3DbFree(pParse->db, pItem->u4.zDatabase);
+    pItem->u4.zDatabase = 0;
+  }
+  pItem->fg.fixedSchema = 0;
+  if( dupSelect ){
+    pSelect = sqlite3SelectDup(pParse->db, pSelect, 0);
+    if( pSelect==0 ) return 0;
+  }
+  p = pItem->u4.pSubq = sqlite3DbMallocRawNN(pParse->db, sizeof(Subquery));
+  if( p==0 ){
+    sqlite3SelectDelete(pParse->db, pSelect);
+    return 0;
+  }
+  pItem->fg.isSubquery = 1;
+  p->pSelect = pSelect;
+  assert( offsetof(Subquery, pSelect)==0 );
+  memset(((char*)p)+sizeof(p->pSelect), 0, sizeof(*p)-sizeof(p->pSelect));
+  return 1;
+}
+
+
+/*
 ** This routine is called by the parser to add a new term to the
 ** end of a growing FROM clause.  The "p" parameter is the part of
 ** the FROM clause that has already been constructed.  "p" is NULL
@@ -5006,10 +5076,12 @@ SrcList *sqlite3SrcListAppendFromTerm(
   if( pAlias->n ){
     pItem->zAlias = sqlite3NameFromToken(db, pAlias);
   }
+  assert( pSubquery==0 || pDatabase==0 );
   if( pSubquery ){
-    pItem->sq.pSelect = pSubquery;
-    if( pSubquery->selFlags & SF_NestedFrom ){
-      pItem->fg.isNestedFrom = 1;
+    if( sqlite3SrcItemAttachSubquery(pParse, pItem, pSubquery, 0) ){
+      if( pSubquery->selFlags & SF_NestedFrom ){
+        pItem->fg.isNestedFrom = 1;
+      }
     }
   }
   assert( pOnUsing==0 || pOnUsing->pOn==0 || pOnUsing->pUsing==0 );