An initial attempt to implement sqlite3_vtab_distinct().

FossilOrigin-Name: d571262d2345bb11e71bef395cf078e5d7303b974b38b4e319adda6194ccc1c5

4 files changed, 48 insertions, 5 deletions

diff --git a/src/loadext.c b/src/loadext.c
index c917e11c8..a4aad7e74 100644
--- a/src/loadext.c
+++ b/src/loadext.c
@@ -488,6 +488,7 @@ static const sqlite3_api_routines sqlite3Apis = {
   /* Version 3.38.0 and later */
   sqlite3_error_offset,
   sqlite3_vtab_rhs_value,
+  sqlite3_vtab_distinct,
 };
 
 /* True if x is the directory separator character
diff --git a/src/sqlite.h.in b/src/sqlite.h.in
index ca27742cb..1e7891112 100644
--- a/src/sqlite.h.in
+++ b/src/sqlite.h.in
@@ -9504,6 +9504,28 @@ int sqlite3_vtab_nochange(sqlite3_context*);
 SQLITE_EXPERIMENTAL const char *sqlite3_vtab_collation(sqlite3_index_info*,int);
 
 /*
+** CAPI3REF: Determine if virtual table query is DISTINCT
+** METHOD: sqlite3_index_info
+**
+** This API may only be used from within an xBestIndex() callback. The
+** results of calling it from outside of an xBestIndex() callback are
+** undefined and probably harmful.
+**
+** ^The sqlite3_vtab_distinct() returns an integer that is either 0, 1, or
+** 2.  ^The sqlite3_vtab_distinct() interface returns 0 if SQLite needs the
+** output rows sorted as defined by the nOrderBy and aOrderBy fields of the
+** [sqlite3_index_info] object P.  ^The sqlite3_vtab_distinct() interface
+** returns 1 if SQLite needs all rows to be returned and for equivalent rows
+** to be adjacent to one another, but if it does not require that the rows
+** be sorted.  ^The sqlite3_vtab_distinct() interface returns 2 if SQLite only
+** needs the virtual table to return rows that are distinct for the columns
+** identified by the nOrderBy and aOrderBy fields of the [sqlite3_index_info]
+** object.  If rows are returned that differ in any of the columns identified
+** by the nOrderBy and aOrderBy fields, then all such rows should be adjacent.
+*/
+int sqlite3_vtab_distinct(sqlite3_index_info*);
+
+/*
 ** CAPI3REF: Constraint values in xBestIndex()
 ** METHOD: sqlite3_index_info
 **
diff --git a/src/sqlite3ext.h b/src/sqlite3ext.h
index 580078b6d..88010b9d8 100644
--- a/src/sqlite3ext.h
+++ b/src/sqlite3ext.h
@@ -347,6 +347,7 @@ struct sqlite3_api_routines {
   /* Version 3.38.0 and later */
   int (*error_offset)(sqlite3*);
   int (*vtab_rhs_value)(sqlite3_index_info*,int,sqlite3_value**);
+  int (*vtab_distinct)(sqlite3_index_info*);
 };
 
 /*
@@ -661,6 +662,7 @@ typedef int (*sqlite3_loadext_entry)(
 /* Version 3.38.0 and later */
 #define sqlite3_error_offset           sqlite3_api->error_offset
 #define sqlite3_vtab_rhs_value         sqlite3_api->vtab_rhs_value
+#define sqlite3_vtab_distinct          sqlite3_api->vtab_distinct
 #endif /* !defined(SQLITE_CORE) && !defined(SQLITE_OMIT_LOAD_EXTENSION) */
 
 #if !defined(SQLITE_CORE) && !defined(SQLITE_OMIT_LOAD_EXTENSION)
diff --git a/src/where.c b/src/where.c
index 3fa7a921d..fe262b36e 100644
--- a/src/where.c
+++ b/src/where.c
@@ -32,6 +32,7 @@ typedef struct HiddenIndexInfo HiddenIndexInfo;
 struct HiddenIndexInfo {
   WhereClause *pWC;        /* The Where clause being analyzed */
   Parse *pParse;           /* The parsing context */
+  int eDistinct;           /* Value to return from sqlite3_vtab_distinct() */
   sqlite3_value *aRhs[1];  /* RHS values for constraints. MUST BE LAST
                            ** because extra space is allocated to hold up
                            ** to nTerm such values */
@@ -1101,15 +1102,15 @@ static SQLITE_NOINLINE void sqlite3ConstructBloomFilter(
 ** by passing the pointer returned by this function to freeIndexInfo().
 */
 static sqlite3_index_info *allocateIndexInfo(
-  Parse *pParse,                  /* The parsing context */
+  WhereInfo *pWInfo,              /* The WHERE clause */
   WhereClause *pWC,               /* The WHERE clause being analyzed */
   Bitmask mUnusable,              /* Ignore terms with these prereqs */
   SrcItem *pSrc,                  /* The FROM clause term that is the vtab */
-  ExprList *pOrderBy,             /* The ORDER BY clause */
   u16 *pmNoOmit                   /* Mask of terms not to omit */
 ){
   int i, j;
   int nTerm;
+  Parse *pParse = pWInfo->pParse;
   struct sqlite3_index_constraint *pIdxCons;
   struct sqlite3_index_orderby *pIdxOrderBy;
   struct sqlite3_index_constraint_usage *pUsage;
@@ -1119,7 +1120,9 @@ static sqlite3_index_info *allocateIndexInfo(
   sqlite3_index_info *pIdxInfo;
   u16 mNoOmit = 0;
   const Table *pTab;
-
+  int eDistinct = 0;
+  ExprList *pOrderBy = pWInfo->pOrderBy;
+ 
   assert( pSrc!=0 );
   pTab = pSrc->pTab;
   assert( pTab!=0 );
@@ -1203,6 +1206,9 @@ static sqlite3_index_info *allocateIndexInfo(
     }
     if( i==n){
       nOrderBy = n;
+      if( (pWInfo->wctrlFlags & WHERE_DISTINCTBY) ){
+        eDistinct = 1;
+      }
     }
   }
 
@@ -1225,6 +1231,7 @@ static sqlite3_index_info *allocateIndexInfo(
   pIdxInfo->aConstraintUsage = pUsage;
   pHidden->pWC = pWC;
   pHidden->pParse = pParse;
+  pHidden->eDistinct = eDistinct;
   for(i=j=0, pTerm=pWC->a; i<pWC->nTerm; i++, pTerm++){
     u16 op;
     if( (pTerm->wtFlags & TERM_OK)==0 ) continue;
@@ -3691,6 +3698,18 @@ int sqlite3_vtab_rhs_value(
   return rc;
 }
 
+
+/*
+** Return true if ORDER BY clause may be handled as DISTINCT.
+*/
+int sqlite3_vtab_distinct(sqlite3_index_info *pIdxInfo){
+  HiddenIndexInfo *pHidden = (HiddenIndexInfo*)&pIdxInfo[1];
+  assert( pHidden->eDistinct==0
+       || pHidden->eDistinct==1
+       || pHidden->eDistinct==2 );
+  return pHidden->eDistinct;
+}
+
 /*
 ** Add all WhereLoop objects for a table of the join identified by
 ** pBuilder->pNew->iTab.  That table is guaranteed to be a virtual table.
@@ -3740,8 +3759,7 @@ static int whereLoopAddVirtual(
   pNew = pBuilder->pNew;
   pSrc = &pWInfo->pTabList->a[pNew->iTab];
   assert( IsVirtual(pSrc->pTab) );
-  p = allocateIndexInfo(pParse, pWC, mUnusable, pSrc, pBuilder->pOrderBy, 
-      &mNoOmit);
+  p = allocateIndexInfo(pWInfo, pWC, mUnusable, pSrc, &mNoOmit);
   if( p==0 ) return SQLITE_NOMEM_BKPT;
   pNew->rSetup = 0;
   pNew->wsFlags = WHERE_VIRTUALTABLE;