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, 29 insertions, 11 deletions

diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 54e4f2db7..c282023de 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -1335,6 +1335,7 @@ typedef struct Savepoint Savepoint;
 typedef struct Select Select;
 typedef struct SQLiteThread SQLiteThread;
 typedef struct SelectDest SelectDest;
+typedef struct Subquery Subquery;
 typedef struct SrcItem SrcItem;
 typedef struct SrcList SrcList;
 typedef struct sqlite3_str StrAccum; /* Internal alias for sqlite3_str */
@@ -3276,6 +3277,16 @@ struct IdList {
 #define EU4_EXPR   2   /* Uses IdList.a.u4.pExpr -- NOT CURRENTLY USED */
 
 /*
+** Details of the implementation of a subquery.
+*/
+struct Subquery {
+  Select *pSelect;  /* A SELECT statement used in place of a table name */
+  int addrFillSub;  /* Address of subroutine to initialize a subquery */
+  int regReturn;    /* Register holding return address of addrFillSub */
+  int regResult;    /* Registers holding results of a co-routine */
+};
+
+/*
 ** The SrcItem object represents a single term in the FROM clause of a query.
 ** The SrcList object is mostly an array of SrcItems.
 **
@@ -3287,10 +3298,15 @@ struct IdList {
 ** In the colUsed field, the high-order bit (bit 63) is set if the table
 ** contains more than 63 columns and the 64-th or later column is used.
 **
+** Intenstive use of "union" helps keep the size of the object small.  This
+** has been shown to boost performance due to less time spend initializing
+** fields to zero when a new instance of this object is allocated.  The unions
+** also help SrcItem, and hence SrcList and Select, use less memory.
+**
 ** Union member validity:
 **
-**    u1.zIndexedBy      fg.isIndexedBy && !fg.isTabFunc
-**    u1.pFuncArg        fg.isTabFunc   && !fg.isIndexedBy
+**    u1.zIndexedBy      fg.isIndexedBy
+**    u1.pFuncArg        fg.isTabFunc
 **    u1.nRow            !fg.isTabFunc  && !fg.isIndexedBy
 **
 **    u2.pIBIndex        fg.isIndexedBy && !fg.isCte
@@ -3299,23 +3315,19 @@ struct IdList {
 **    u3.pOn             fg.isUsing==0
 **    u3.pUsing          fg.isUsing==1
 **
-**    u4.zDatabase       fg.fixedSchema==0
+**    u4.zDatabase       fg.fixedSchema==0 && !fg.isSubquery
 **    u4.pSchema         fg.fixedSchema==1
+**    u4.pSubq           fg.isSubquery
 */
 struct SrcItem {
   char *zName;      /* Name of the table */
   char *zAlias;     /* The "B" part of a "A AS B" phrase.  zName is the "A" */
   Table *pSTab;     /* Table object for zName. Mnemonic: Srcitem-TABle */
-  struct SrcItemSubquery {
-    Select *pSelect;  /* A SELECT statement used in place of a table name */
-    int addrFillSub;  /* Address of subroutine to initialize a subquery */
-    int regReturn;    /* Register holding return address of addrFillSub */
-    int regResult;    /* Registers holding results of a co-routine */
-  } sq;
   struct {
     u8 jointype;      /* Type of join between this table and the previous */
     unsigned notIndexed :1;    /* True if there is a NOT INDEXED clause */
     unsigned isIndexedBy :1;   /* True if there is an INDEXED BY clause */
+    unsigned isSubquery :1;    /* True if this term is a subquery */
     unsigned isTabFunc :1;     /* True if table-valued-function syntax */
     unsigned isCorrelated :1;  /* True if sub-query is correlated */
     unsigned isMaterialized:1; /* This is a materialized view */
@@ -3350,6 +3362,7 @@ struct SrcItem {
   union {
     Schema *pSchema;  /* Schema to which this item is fixed */
     char *zDatabase;  /* Name of database holding this table */
+    Subquery *pSubq;  /* Description of a subquery */
   } u4;
 };
 
@@ -3610,8 +3623,10 @@ struct Select {
 #define SF_UpdateFrom   0x10000000 /* Query originates with UPDATE FROM */
 #define SF_Correlated   0x20000000 /* True if references the outer context */
 
-/* True if S exists and has SF_NestedFrom */
-#define IsNestedFrom(S) ((S)!=0 && ((S)->selFlags&SF_NestedFrom)!=0)
+/* True if SrcList item X is a subquery that has SF_NestedFrom */
+#define IsNestedFrom(X) \
+   ((X)->fg.isSubquery && \
+    ((X)->u4.pSubq->pSelect->selFlags&SF_NestedFrom)!=0)
 
 /*
 ** The results of a SELECT can be distributed in several ways, as defined
@@ -5003,6 +5018,9 @@ int sqlite3IdListIndex(IdList*,const char*);
 SrcList *sqlite3SrcListEnlarge(Parse*, SrcList*, int, int);
 SrcList *sqlite3SrcListAppendList(Parse *pParse, SrcList *p1, SrcList *p2);
 SrcList *sqlite3SrcListAppend(Parse*, SrcList*, Token*, Token*);
+void sqlite3SubqueryDelete(sqlite3*,Subquery*);
+Select *sqlite3SubqueryDetach(sqlite3*,SrcItem*);
+int sqlite3SrcItemAttachSubquery(Parse*, SrcItem*, Select*, int);
 SrcList *sqlite3SrcListAppendFromTerm(Parse*, SrcList*, Token*, Token*,
                                       Token*, Select*, OnOrUsing*);
 void sqlite3SrcListIndexedBy(Parse *, SrcList *, Token *);