Performance optimization: Avoid calling convertCompoundSelecctToSubquery()

on queries that do not use the UNION, EXCEPT, or INTERSECT operators.

FossilOrigin-Name: c589b2fed7beabc2337d701094c22635914d9c23

src/parse.y

@@ -417,6 +417,7 @@ select(A) ::= select(X) multiselect_op(Y) oneselect(Z).  {
   if( Z ){
     Z->op = (u8)Y;
     Z->pPrior = X;
+    if( Y!=TK_ALL ) pParse->hasCompound = 1;
   }else{
     sqlite3SelectDelete(pParse->db, X);
   }

src/select.c

@@ -3639,10 +3639,12 @@ static int exprWalkNoop(Walker *NotUsed, Expr *NotUsed2){
 static void sqlite3SelectExpand(Parse *pParse, Select *pSelect){
   Walker w;
   memset(&w, 0, sizeof(w));
-  w.xSelectCallback = convertCompoundSelectToSubquery;
   w.xExprCallback = exprWalkNoop;
   w.pParse = pParse;
-  sqlite3WalkSelect(&w, pSelect);
+  if( pParse->hasCompound ){
+    w.xSelectCallback = convertCompoundSelectToSubquery;
+    sqlite3WalkSelect(&w, pSelect);
+  }
   w.xSelectCallback = selectExpander;
   sqlite3WalkSelect(&w, pSelect);
 }

src/sqliteInt.h

@@ -2078,6 +2078,7 @@ struct Select {
 #define SF_Values          0x0080  /* Synthesized from VALUES clause */
 #define SF_Materialize     0x0100  /* Force materialization of views */
 #define SF_NestedFrom      0x0200  /* Part of a parenthesized FROM clause */
+#define SF_MaybeConvert    0x0400  /* Need convertCompoundSelectToSubquery() */
 
 
 /*
@@ -2199,6 +2200,7 @@ struct Parse {
   u8 iColCache;        /* Next entry in aColCache[] to replace */
   u8 isMultiWrite;     /* True if statement may modify/insert multiple rows */
   u8 mayAbort;         /* True if statement may throw an ABORT exception */
+  u8 hasCompound;      /* Need to invoke convertCompoundSelectToSubquery() */
   int aTempReg[8];     /* Holding area for temporary registers */
   int nRangeReg;       /* Size of the temporary register block */
   int iRangeReg;       /* First register in temporary register block */