If a query like "SELECT min(a), b FROM t1" visits no rows where "a" is not null, extract a value for "b" from one of the rows where "a" is null. Fix for ticket [41866dc37].

FossilOrigin-Name: faaaae4940b5f4f70e4988ad5b45582410b381ace0031e6abcde0b9217c06796

1 files changed, 19 insertions, 0 deletions

diff --git a/src/wherecode.c b/src/wherecode.c
index a62544845..6152f7c35 100644
--- a/src/wherecode.c
+++ b/src/wherecode.c
@@ -1694,6 +1694,25 @@ Bitmask sqlite3WhereCodeOneLoopStart(
       VdbeCoverageIf(v, op==OP_SeekGE);  testcase( op==OP_SeekGE );
       VdbeCoverageIf(v, op==OP_SeekLE);  testcase( op==OP_SeekLE );
       VdbeCoverageIf(v, op==OP_SeekLT);  testcase( op==OP_SeekLT );
+
+      if( bSeekPastNull && (pLoop->wsFlags & WHERE_TOP_LIMIT)==0 ){
+        /* If bSeekPastNull is set only to skip past the NULL values for
+        ** a query like "SELECT min(a), b FROM t1", then add code so that
+        ** if there are no rows with (a IS NOT NULL), then do the seek 
+        ** without jumping past NULLs instead. This allows the code in 
+        ** select.c to pick a value for "b" in the above query.  */
+        assert( startEq==0 && (op==OP_SeekGT || op==OP_SeekLT) );
+        assert( (pWInfo->wctrlFlags&WHERE_ORDERBY_MIN)!=0 && pWInfo->nOBSat>0 );
+        sqlite3VdbeChangeP2(v, -1, sqlite3VdbeCurrentAddr(v)+1);
+        sqlite3VdbeAddOp2(v, OP_Goto, 0, sqlite3VdbeCurrentAddr(v)+2);
+
+        op = aStartOp[(start_constraints<<2) + (1<<1) + bRev];
+        assert( op!=0 );
+        sqlite3VdbeAddOp4Int(v, op, iIdxCur, addrNxt, regBase, nConstraint);
+        VdbeCoverage(v);
+        VdbeCoverageIf(v, op==OP_SeekGE);  testcase( op==OP_SeekGE );
+        VdbeCoverageIf(v, op==OP_SeekLE);  testcase( op==OP_SeekLE );
+      }
     }
 
     /* Load the value for the inequality constraint at the end of the