Changes to EXPLAIN QUERY PLAN to identify covering index plan that use indexes on expressions.

FossilOrigin-Name: 29fb4919b6118b3b9ae411ec2ed5b59db7fae281909501c5fa238221ba635db5

1 files changed, 50 insertions, 15 deletions

diff --git a/src/wherecode.c b/src/wherecode.c
index 0951e5e20..f1c6711af 100644
--- a/src/wherecode.c
+++ b/src/wherecode.c
@@ -110,27 +110,24 @@ static void explainIndexRange(StrAccum *pStr, WhereLoop *pLoop){
 }
 
 /*
-** This function is a no-op unless currently processing an EXPLAIN QUERY PLAN
-** command, or if stmt_scanstatus_v2() stats are enabled, or if SQLITE_DEBUG
-** was defined at compile-time. If it is not a no-op, a single OP_Explain
-** opcode is added to the output to describe the table scan strategy in pLevel.
-**
-** If an OP_Explain opcode is added to the VM, its address is returned.
-** Otherwise, if no OP_Explain is coded, zero is returned.
+** This function sets the P4 value of an existing OP_Explain opcode to 
+** text describing the loop in pLevel. If the OP_Explain opcode already has
+** a P4 value, it is freed before it is overwritten.
 */
-int sqlite3WhereExplainOneScan(
+void sqlite3WhereAddExplainText(
   Parse *pParse,                  /* Parse context */
+  int addr,                       /* Address of OP_Explain opcode */
   SrcList *pTabList,              /* Table list this loop refers to */
   WhereLevel *pLevel,             /* Scan to write OP_Explain opcode for */
   u16 wctrlFlags                  /* Flags passed to sqlite3WhereBegin() */
 ){
-  int ret = 0;
 #if !defined(SQLITE_DEBUG)
   if( sqlite3ParseToplevel(pParse)->explain==2 || IS_STMT_SCANSTATUS(pParse->db) )
 #endif
   {
+    VdbeOp *pOp = sqlite3VdbeGetOp(pParse->pVdbe, addr);
+
     SrcItem *pItem = &pTabList->a[pLevel->iFrom];
-    Vdbe *v = pParse->pVdbe;      /* VM being constructed */
     sqlite3 *db = pParse->db;     /* Database handle */
     int isSearch;                 /* True for a SEARCH. False for SCAN. */
     WhereLoop *pLoop;             /* The controlling WhereLoop object */
@@ -139,9 +136,10 @@ int sqlite3WhereExplainOneScan(
     StrAccum str;                 /* EQP output string */
     char zBuf[100];               /* Initial space for EQP output string */
 
+    if( db->mallocFailed ) return;
+
     pLoop = pLevel->pWLoop;
     flags = pLoop->wsFlags;
-    if( (flags&WHERE_MULTI_OR) || (wctrlFlags&WHERE_OR_SUBCLAUSE) ) return 0;
 
     isSearch = (flags&(WHERE_BTM_LIMIT|WHERE_TOP_LIMIT))!=0
             || ((flags&WHERE_VIRTUALTABLE)==0 && (pLoop->u.btree.nEq>0))
@@ -165,7 +163,7 @@ int sqlite3WhereExplainOneScan(
         zFmt = "AUTOMATIC PARTIAL COVERING INDEX";
       }else if( flags & WHERE_AUTO_INDEX ){
         zFmt = "AUTOMATIC COVERING INDEX";
-      }else if( flags & WHERE_IDX_ONLY ){
+      }else if( flags & (WHERE_IDX_ONLY|WHERE_EXPRIDX) ){
         zFmt = "COVERING INDEX %s";
       }else{
         zFmt = "INDEX %s";
@@ -219,9 +217,46 @@ int sqlite3WhereExplainOneScan(
 #endif
     zMsg = sqlite3StrAccumFinish(&str);
     sqlite3ExplainBreakpoint("",zMsg);
-    ret = sqlite3VdbeAddOp4(v, OP_Explain, sqlite3VdbeCurrentAddr(v),
-                            pParse->addrExplain, pLoop->rRun,
-                            zMsg, P4_DYNAMIC);
+
+    assert( pOp->opcode==OP_Explain );
+    assert( pOp->p4type==P4_DYNAMIC || pOp->p4.z==0 );
+    sqlite3DbFree(db, pOp->p4.z);
+    pOp->p4type = P4_DYNAMIC;
+    pOp->p4.z = sqlite3StrAccumFinish(&str);
+  }
+}
+
+
+/*
+** This function is a no-op unless currently processing an EXPLAIN QUERY PLAN
+** command, or if stmt_scanstatus_v2() stats are enabled, or if SQLITE_DEBUG
+** was defined at compile-time. If it is not a no-op, a single OP_Explain
+** opcode is added to the output to describe the table scan strategy in pLevel.
+**
+** If an OP_Explain opcode is added to the VM, its address is returned.
+** Otherwise, if no OP_Explain is coded, zero is returned.
+*/
+int sqlite3WhereExplainOneScan(
+  Parse *pParse,                  /* Parse context */
+  SrcList *pTabList,              /* Table list this loop refers to */
+  WhereLevel *pLevel,             /* Scan to write OP_Explain opcode for */
+  u16 wctrlFlags                  /* Flags passed to sqlite3WhereBegin() */
+){
+  int ret = 0;
+#if !defined(SQLITE_DEBUG)
+  if( sqlite3ParseToplevel(pParse)->explain==2 || IS_STMT_SCANSTATUS(pParse->db) )
+#endif
+  {
+    if( (pLevel->pWLoop->wsFlags & WHERE_MULTI_OR)==0
+     && (wctrlFlags & WHERE_OR_SUBCLAUSE)==0
+    ){
+      Vdbe *v = pParse->pVdbe;
+      int addr = sqlite3VdbeCurrentAddr(v);
+      ret = sqlite3VdbeAddOp3(
+          v, OP_Explain, addr, pParse->addrExplain, pLevel->pWLoop->rRun
+      );
+      sqlite3WhereAddExplainText(pParse, addr, pTabList, pLevel, wctrlFlags);
+    }
   }
   return ret;
 }