Improved estimate on the number of output rows in a recursive common table expression

that uses the UNION operator.  Follow-up to [f911f1c4977fbcae] and it's output row
estimate changes associated with DISTINCT queries.

FossilOrigin-Name: 92513f6bce7ecc778e78af3a77bc66ff65585fffa2e3138f8acb9e617121eeb0

1 files changed, 6 insertions, 0 deletions

diff --git a/src/select.c b/src/select.c
index 91690c327..6e8ee58bc 100644
--- a/src/select.c
+++ b/src/select.c
@@ -8119,6 +8119,12 @@ int sqlite3Select(
     if( pWInfo==0 ) goto select_end;
     if( sqlite3WhereOutputRowCount(pWInfo) < p->nSelectRow ){
       p->nSelectRow = sqlite3WhereOutputRowCount(pWInfo);
+      if( pDest->eDest<=SRT_DistQueue && pDest->eDest>=SRT_DistFifo ){
+        /* TUNING: For a UNION CTE, because UNION is implies DISTINCT,
+        ** reduce the estimated output row count by 8 (LogEst 30). 
+        ** Search for tag-20250414a to see other cases */
+        p->nSelectRow -= 30;
+      }
     }
     if( sDistinct.isTnct && sqlite3WhereIsDistinct(pWInfo) ){
       sDistinct.eTnctType = sqlite3WhereIsDistinct(pWInfo);