/*
 * TSqlAgg.prg — GROUP BY aggregation and HAVING filter
 *
 * FiveSql — SQL Engine for Harbour DBF/NTX
 *
 * Copyright (c) 2025 Charles KWON (Charles KWON OhJun)
 * Email: charleskwonohjun@gmail.com
 *
 * All rights reserved.
 */

#include "hbclass.ch"
#include "FiveSqlDef.ch"

CLASS TSqlAgg

   METHOD New() CONSTRUCTOR
   METHOD GroupBy( aRows, aFN, aCols, aGroupBy, xHaving, aTables, aParams )
   METHOD FindGroupIdx( xGroupExpr, aCols, aFN )
   METHOD ExpandGroupingSets( aGroupBy )
   METHOD ExprInSet( xSelExpr, aSet )
   METHOD ComputeAgg( xE, aGR, aFN )
   METHOD FindColIdx( xExpr, aFN )
   METHOD FindColIdx2( cN, aFN )
   METHOD EvalHaving( xHaving, aNewRow, aCols, aGroupRows, aFN, aParams )
   METHOD HasAgg( aCols )
   METHOD EvalHavingExpr( xE, aNewRow, aCols, aGR, aFN, aParams )

ENDCLASS


METHOD New() CLASS TSqlAgg
RETURN SELF


METHOD HasAgg( aCols ) CLASS TSqlAgg

   LOCAL i

   FOR i := 1 TO Len( aCols )
      IF SqlExprHasAgg( aCols[ i ][ 1 ] )
         RETURN .T.
      ENDIF
   NEXT

RETURN .F.


METHOD GroupBy( aRows, aFN, aCols, aGroupBy, xHaving, aTables, aParams ) CLASS TSqlAgg

   LOCAL i, j, aGroupRows, aResult := {}
   LOCAL aNewRow
   LOCAL nGCol, cN, nCI, lPass
   LOCAL aGroupIdx := {}
   LOCAL aSets, aCurSet, nSet, hOmitIdx, aSubResult
   LOCAL aGroupedRows
   LOCAL aColInfo  /* { lIsAgg, nCI } per SELECT column, pre-resolved */
   LOCAL xAggNode, cAggFn

   /* Aggregate on empty set — SQL standard semantics:
    *   COUNT(*) / COUNT(col) → 0
    *   SUM / AVG / MIN / MAX → NULL
    * The old code returned 0 uniformly for every aggregate, which
    * looked right for COUNT but silently corrupted the other four. */
   IF Len( aRows ) == 0 .AND. ::HasAgg( aCols )
      aNewRow := {}
      FOR j := 1 TO Len( aCols )
         IF SqlExprHasAgg( aCols[ j ][ 1 ] )
            xAggNode := aCols[ j ][ 1 ]
            cAggFn := ""
            IF ValType( xAggNode ) == "A" .AND. Len( xAggNode ) >= 2 .AND. ;
               xAggNode[ 1 ] == ND_FN .AND. ValType( xAggNode[ 2 ] ) == "C"
               cAggFn := Upper( xAggNode[ 2 ] )
            ENDIF
            IF cAggFn == "COUNT"
               AAdd( aNewRow, 0 )
            ELSE
               AAdd( aNewRow, NIL )
            ENDIF
         ELSE
            AAdd( aNewRow, NIL )
         ENDIF
      NEXT
      RETURN { aNewRow }
   ENDIF

   /* SQL:2003 ROLLUP / CUBE / GROUPING SETS — expand into a list of
    * flat grouping key sets and run aggregation once per set. Columns
    * absent from the current set emit NIL (the standard "subtotal"
    * placeholder). */
   aSets := ::ExpandGroupingSets( aGroupBy )
   IF Len( aSets ) > 1
      FOR nSet := 1 TO Len( aSets )
         aCurSet := aSets[ nSet ]
         /* Recurse with the plain expanded set; no ROLLUP/CUBE nodes */
         aSubResult := ::GroupBy( aRows, aFN, aCols, aCurSet, xHaving, aTables, aParams )
         /* For each result row, NIL-out any SELECT column whose source
          * GROUP BY expression is not in the current set. */
         hOmitIdx := { => }
         FOR i := 1 TO Len( aCols )
            IF ! SqlExprHasAgg( aCols[ i ][ 1 ] )
               IF ! ::ExprInSet( aCols[ i ][ 1 ], aCurSet )
                  hOmitIdx[ i ] := .T.
               ENDIF
            ENDIF
         NEXT
         FOR i := 1 TO Len( aSubResult )
            FOR j := 1 TO Len( aSubResult[ i ] )
               IF hb_HHasKey( hOmitIdx, j )
                  aSubResult[ i ][ j ] := NIL
               ENDIF
            NEXT
            AAdd( aResult, aSubResult[ i ] )
         NEXT
      NEXT
      RETURN aResult
   ENDIF

   /* Build group buckets.
    * Pre-resolve the GROUP BY columns to their position in the SELECT
    * list by matching against the SOURCE expressions in aCols, not the
    * alias list in aFN. */
   FOR j := 1 TO Len( aGroupBy )
      nGCol := ::FindGroupIdx( aGroupBy[ j ], aCols, aFN )
      AAdd( aGroupIdx, nGCol )
   NEXT

   /* Grouping step — delegate to Go RTL SqlGroupRows to collapse
    * N·M per-row boundary crossings (SqlValToStr / hb_HHasKey / AAdd)
    * into a single call. Aggregates and HAVING stay in PRG because
    * they touch too many expression kinds to port cleanly. */
   IF Len( aGroupBy ) == 0 .AND. ::HasAgg( aCols )
      aGroupedRows := { aRows }
   ELSE
      aGroupedRows := SqlGroupRows( aRows, aGroupIdx )
   ENDIF

   /* Pre-resolve per SELECT column: aggregate flag + column index.
    * Avoids SqlExprHasAgg + SqlExprName + FindColIdx2 per group. */
   aColInfo := Array( Len( aCols ) )
   FOR j := 1 TO Len( aCols )
      IF SqlExprHasAgg( aCols[ j ][ 1 ] )
         aColInfo[ j ] := { .T., 0 }
      ELSE
         cN := SqlExprName( aCols[ j ][ 1 ] )
         nCI := ::FindColIdx2( cN, aFN )
         aColInfo[ j ] := { .F., nCI }
      ENDIF
   NEXT

   /* Compute aggregates for each group */
   FOR EACH aGroupRows IN aGroupedRows
      aNewRow := Array( Len( aCols ) )
      FOR j := 1 TO Len( aCols )
         IF aColInfo[ j ][ 1 ]
            aNewRow[ j ] := ::ComputeAgg( aCols[ j ][ 1 ], aGroupRows, aFN )
         ELSE
            nCI := aColInfo[ j ][ 2 ]
            IF nCI > 0 .AND. Len( aGroupRows ) > 0 .AND. nCI <= Len( aGroupRows[ 1 ] )
               aNewRow[ j ] := aGroupRows[ 1 ][ nCI ]
            ENDIF
         ENDIF
      NEXT

      /* HAVING filter */
      IF xHaving != NIL
         lPass := ::EvalHaving( xHaving, aNewRow, aCols, aGroupRows, aFN, aParams )
         IF ! lPass
            LOOP
         ENDIF
      ENDIF

      AAdd( aResult, aNewRow )
   NEXT

RETURN aResult


/* Expand SQL:2003 ROLLUP / CUBE / GROUPING SETS into a list of flat
 * grouping sets. Each returned set is an array of expressions that
 * would be the plain GROUP BY for one pass of aggregation.
 *
 *   GROUP BY a, ROLLUP(b, c)         → {(a,b,c), (a,b), (a)}
 *   GROUP BY CUBE(a, b)              → {(a,b), (a), (b), ()}
 *   GROUP BY GROUPING SETS ((a,b), (a), ())  → as-is
 *
 * If aGroupBy is a plain column list with no aggregate-set modifiers,
 * returns a single-element list with aGroupBy itself — letting the
 * caller short-circuit to the fast path unchanged.
 */
METHOD ExpandGroupingSets( aGroupBy ) CLASS TSqlAgg

   LOCAL aSets, aCurrent, i, j, xTerm, aExpand, aNewSets, aBase
   LOCAL nBits, nMask, bit, aCubeSet

   /* Fast path: no ROLLUP/CUBE/GROUPING SETS node → single set */
   aExpand := .F.
   FOR i := 1 TO Len( aGroupBy )
      IF aGroupBy[ i ] != NIL .AND. ValType( aGroupBy[ i ] ) == "A" .AND. ;
         aGroupBy[ i ][ 1 ] == ND_FN .AND. ;
         ( Upper( aGroupBy[ i ][ 2 ] ) == "ROLLUP" .OR. ;
           Upper( aGroupBy[ i ][ 2 ] ) == "CUBE" .OR. ;
           Upper( aGroupBy[ i ][ 2 ] ) == "GROUPING SETS" )
         aExpand := .T.
         EXIT
      ENDIF
   NEXT
   IF ! aExpand
      RETURN { aGroupBy }
   ENDIF

   /* Seed with a single empty set — we'll cross-expand each term */
   aSets := { {} }

   FOR i := 1 TO Len( aGroupBy )
      xTerm := aGroupBy[ i ]
      aNewSets := {}

      IF xTerm != NIL .AND. ValType( xTerm ) == "A" .AND. xTerm[ 1 ] == ND_FN
         DO CASE
         CASE Upper( xTerm[ 2 ] ) == "ROLLUP"
            /* ROLLUP(c1..cN) → N+1 sets:
             *   (c1..cN), (c1..cN-1), ..., (c1), ()
             * Cross-product: existing × each prefix including empty */
            aBase := xTerm[ 3 ]
            FOR j := 1 TO Len( aSets )
               FOR nBits := Len( aBase ) TO 0 STEP -1
                  aCurrent := AClone( aSets[ j ] )
                  FOR nMask := 1 TO nBits
                     AAdd( aCurrent, aBase[ nMask ] )
                  NEXT
                  AAdd( aNewSets, aCurrent )
               NEXT
            NEXT

         CASE Upper( xTerm[ 2 ] ) == "CUBE"
            /* CUBE(c1..cN) → 2^N sets (every subset).
             * For each bitmask, include cols where bit is set. */
            aBase := xTerm[ 3 ]
            FOR j := 1 TO Len( aSets )
               FOR nMask := 0 TO ( 2 ^ Len( aBase ) ) - 1
                  aCurrent := AClone( aSets[ j ] )
                  FOR bit := 1 TO Len( aBase )
                     IF hb_BitAnd( nMask, hb_BitShift( 1, bit - 1 ) ) != 0
                        AAdd( aCurrent, aBase[ bit ] )
                     ENDIF
                  NEXT
                  AAdd( aNewSets, aCurrent )
               NEXT
            NEXT

         CASE Upper( xTerm[ 2 ] ) == "GROUPING SETS"
            /* Explicit list — each element is a flat list of cols (or ()) */
            aBase := xTerm[ 3 ]
            FOR j := 1 TO Len( aSets )
               FOR nBits := 1 TO Len( aBase )
                  aCurrent := AClone( aSets[ j ] )
                  IF ValType( aBase[ nBits ] ) == "A"
                     FOR nMask := 1 TO Len( aBase[ nBits ] )
                        AAdd( aCurrent, aBase[ nBits ][ nMask ] )
                     NEXT
                  ENDIF
                  AAdd( aNewSets, aCurrent )
               NEXT
            NEXT

         OTHERWISE
            /* Unknown ND_FN in GROUP BY — treat as opaque term */
            FOR j := 1 TO Len( aSets )
               aCurrent := AClone( aSets[ j ] )
               AAdd( aCurrent, xTerm )
               AAdd( aNewSets, aCurrent )
            NEXT
         ENDCASE
      ELSE
         /* Plain column — append to every existing set */
         FOR j := 1 TO Len( aSets )
            aCurrent := AClone( aSets[ j ] )
            AAdd( aCurrent, xTerm )
            AAdd( aNewSets, aCurrent )
         NEXT
      ENDIF

      aSets := aNewSets
   NEXT

RETURN aSets


/* Does a SELECT expression reference a column that appears in the
 * given grouping set? Used to decide which SELECT cols to NIL out
 * when reporting a partial grouping (subtotal) row. */
METHOD ExprInSet( xSelExpr, aSet ) CLASS TSqlAgg

   LOCAL i, xG, cSelName, cGName, nDot

   IF xSelExpr == NIL .OR. xSelExpr[ 1 ] != ND_COL
      RETURN .F.
   ENDIF

   cSelName := Upper( xSelExpr[ 2 ] )
   nDot := At( ".", cSelName )
   IF nDot > 0
      cSelName := SubStr( cSelName, nDot + 1 )
   ENDIF

   FOR i := 1 TO Len( aSet )
      xG := aSet[ i ]
      IF xG != NIL .AND. ValType( xG ) == "A" .AND. xG[ 1 ] == ND_COL
         cGName := Upper( xG[ 2 ] )
         IF "." $ cGName
            cGName := SubStr( cGName, At( ".", cGName ) + 1 )
         ENDIF
         IF cGName == cSelName
            RETURN .T.
         ENDIF
      ENDIF
   NEXT

RETURN .F.


/* Resolve a GROUP BY expression to its column position in the output row.
 * Walks the SELECT list's source expressions (aCols[i][1]) rather than
 * the alias list (aFN[i]). For `SELECT d.name AS foo GROUP BY d.name`,
 * aFN is {"FOO"} but aCols[1][1] is ND_COL "d.name" — we need to match
 * the latter, otherwise the group key collapses every row into one
 * bucket. Falls back to FindColIdx (alias/name lookup) for cases where
 * the GROUP BY uses a simple identifier that isn't in the SELECT list.
 */
METHOD FindGroupIdx( xGroupExpr, aCols, aFN ) CLASS TSqlAgg

   LOCAL i, xSel, cGName, cSName, nDot, nOrdinal

   IF xGroupExpr == NIL
      RETURN 0
   ENDIF

   /* GROUP BY <ordinal> — `GROUP BY 1` refers to the 1-based position
    * of the SELECT-list column, per SQL:1999. Without this the
    * literal numeric expression got passed to FindColIdx which only
    * understands ND_COL → returned 0 → everything collapsed into
    * a single bucket. */
   IF xGroupExpr[ 1 ] == ND_LIT .AND. ValType( xGroupExpr[ 2 ] ) == "N"
      nOrdinal := Int( xGroupExpr[ 2 ] )
      IF nOrdinal >= 1 .AND. nOrdinal <= Len( aCols )
         RETURN nOrdinal
      ENDIF
      RETURN 0
   ENDIF

   /* GROUP BY <expression> — match against the SELECT list by
    * canonical name. Both sides go through SqlExprName so that
    * `GROUP BY UPPER(dept)` finds `SELECT UPPER(dept)` even when
    * the SELECT-list column is anonymous. Same for arithmetic
    * expressions like `salary / 1000`. */
   IF xGroupExpr[ 1 ] != ND_COL
      cGName := Upper( SqlExprName( xGroupExpr ) )
      IF ! Empty( cGName )
         FOR i := 1 TO Len( aCols )
            cSName := Upper( SqlExprName( aCols[ i ][ 1 ] ) )
            IF cSName == cGName
               RETURN i
            ENDIF
         NEXT
      ENDIF
      RETURN ::FindColIdx( xGroupExpr, aFN )
   ENDIF

   cGName := Upper( xGroupExpr[ 2 ] )
   nDot := At( ".", cGName )
   IF nDot > 0
      cGName := SubStr( cGName, nDot + 1 )
   ENDIF

   FOR i := 1 TO Len( aCols )
      xSel := aCols[ i ][ 1 ]
      IF xSel != NIL .AND. xSel[ 1 ] == ND_COL
         cSName := Upper( xSel[ 2 ] )
         IF "." $ cSName
            cSName := SubStr( cSName, At( ".", cSName ) + 1 )
         ENDIF
         IF cSName == cGName
            RETURN i
         ENDIF
      ENDIF
   NEXT

   /* Last resort: alias-based lookup (handles GROUP BY of unrelated cols) */
RETURN ::FindColIdx( xGroupExpr, aFN )


METHOD FindColIdx( xExpr, aFN ) CLASS TSqlAgg

   LOCAL cN, i

   IF xExpr != NIL .AND. xExpr[ 1 ] == ND_COL
      cN := Upper( xExpr[ 2 ] )
      IF "." $ cN
         cN := SubStr( cN, At( ".", cN ) + 1 )
      ENDIF
      FOR i := 1 TO Len( aFN )
         IF Upper( aFN[ i ] ) == cN
            RETURN i
         ENDIF
      NEXT
   ENDIF

RETURN 0


METHOD FindColIdx2( cN, aFN ) CLASS TSqlAgg

   LOCAL i

   cN := Upper( cN )
   FOR i := 1 TO Len( aFN )
      IF Upper( aFN[ i ] ) == cN
         RETURN i
      ENDIF
   NEXT

RETURN 0


METHOD ComputeAgg( xE, aGR, aFN ) CLASS TSqlAgg

   LOCAL cFunc, cArgName, nCol, i, xVal
   LOCAL nCount := 0, nSum := 0, xMin := NIL, xMax := NIL
   LOCAL cResult, cSep
   LOCAL xArg
   LOCAL xL, xR, aFnArgs
   LOCAL lDistinct, hSeen, cKey

   IF xE == NIL
      RETURN 0
   ENDIF

   /* Outer expression containing aggregates (e.g. MAX(id)+1,
    * COUNT(*)*2, SUM(v)-30): the dispatcher routes us here whenever
    * SqlExprHasAgg is .T., even if the top-level node is not the
    * aggregate itself. Recursively compute inner aggregates, then
    * apply the wrapping operator via SqlEvalRowExpr against literal
    * stand-ins. Without this guard the early-return below collapsed
    * every wrapped aggregate to 0 — silently. */
   IF xE[ 1 ] == ND_BIN
      xL := ::ComputeAgg( xE[ 3 ], aGR, aFN )
      xR := ::ComputeAgg( xE[ 4 ], aGR, aFN )
      RETURN SqlEvalRowExpr( ;
         { ND_BIN, xE[ 2 ], { ND_LIT, xL }, { ND_LIT, xR } }, {}, {} )
   ENDIF

   IF xE[ 1 ] == ND_UNI
      xL := ::ComputeAgg( xE[ 3 ], aGR, aFN )
      RETURN SqlEvalRowExpr( ;
         { ND_UNI, xE[ 2 ], { ND_LIT, xL } }, {}, {} )
   ENDIF

   IF xE[ 1 ] == ND_LIT
      RETURN xE[ 2 ]
   ENDIF

   IF xE[ 1 ] == ND_NIL
      RETURN NIL
   ENDIF

   /* Non-aggregate function wrapping aggregates: ROUND(AVG(p),2),
    * COALESCE(SUM(x), 0), etc. Recurse into each arg, then dispatch. */
   IF xE[ 1 ] == ND_FN .AND. ! SqlIsAggName( xE[ 2 ] )
      aFnArgs := {}
      FOR i := 1 TO Len( xE[ 3 ] )
         AAdd( aFnArgs, ::ComputeAgg( xE[ 3 ][ i ], aGR, aFN ) )
      NEXT
      RETURN SqlEvalFunc( xE[ 2 ], aFnArgs )
   ENDIF

   /* CASE wrapping aggregates: `CASE WHEN COUNT(*) > 2 THEN 'many'
    * ELSE 'few' END`. SqlExprHasAgg flags the whole CASE as having
    * an aggregate, the dispatcher routes here, and the early-out
    * below collapsed it to 0 — the literal 'many'/'few' came back
    * as 0. Evaluate each WHEN cond + branch / ELSE through the same
    * recursive ComputeAgg so the aggregate inside the cond gets
    * computed once per group. */
   IF xE[ 1 ] == ND_CASE
      IF ValType( xE[ 2 ] ) == "A"
         FOR i := 1 TO Len( xE[ 2 ] )
            xL := ::ComputeAgg( xE[ 2 ][ i ][ 1 ], aGR, aFN )
            IF SqlIsTrue( xL )
               RETURN ::ComputeAgg( xE[ 2 ][ i ][ 2 ], aGR, aFN )
            ENDIF
         NEXT
      ENDIF
      IF Len( xE ) >= 3 .AND. xE[ 3 ] != NIL
         RETURN ::ComputeAgg( xE[ 3 ], aGR, aFN )
      ENDIF
      RETURN NIL
   ENDIF

   IF xE[ 1 ] != ND_FN
      RETURN 0
   ENDIF

   cFunc := Upper( xE[ 2 ] )

   IF Len( xE[ 3 ] ) > 0
      xArg := xE[ 3 ][ 1 ]
      IF xArg[ 1 ] == ND_COL .AND. xArg[ 2 ] == "*"
         IF cFunc == "COUNT"
            RETURN Len( aGR )
         ENDIF
         RETURN 0
      ENDIF
      cArgName := SqlExprName( xArg )
   ELSE
      IF cFunc == "COUNT"
         RETURN Len( aGR )
      ENDIF
      RETURN 0
   ENDIF

   nCol := ::FindColIdx2( cArgName, aFN )
   /* Also try the QUALIFIED name from the AST (e.g. "o.amount") since
    * the Go SqlHashJoin fast path preserves qualifier prefixes in
    * aFieldNames for JOIN disambiguation. SqlExprName strips them
    * but the hidden column might be stored with the full qualified form. */
   IF nCol == 0 .AND. xArg[ 1 ] == ND_COL .AND. xArg[ 2 ] != cArgName
      nCol := ::FindColIdx2( Upper( xArg[ 2 ] ), aFN )
   ENDIF
   IF nCol == 0 .AND. xArg[ 1 ] == ND_COL
      IF cFunc == "COUNT"
         RETURN Len( aGR )
      ENDIF
      RETURN 0
   ENDIF

   /* DISTINCT modifier: parser stashes a .T. flag in xE[5] when the
    * aggregate was written `COUNT(DISTINCT col)` etc. PRG path needs
    * a per-value seen-set so duplicates contribute once. Fast path
    * (SqlComputeAggSimple) has no DISTINCT support — skip it when
    * the modifier is set so PRG handles dedup. */
   lDistinct := ( Len( xE ) >= 5 .AND. xE[ 5 ] == .T. )

   /* Fast path: plain column + common aggregate → Go RTL single-pass loop.
    * Gate on column-ref argument + pre-resolved nCol > 0; complex args
    * (CASE/BIN/UDF) still fall through to the PRG loop below. */
   IF ! lDistinct .AND. nCol > 0 .AND. xArg[ 1 ] == ND_COL .AND. ;
      ( cFunc == "COUNT" .OR. cFunc == "SUM" .OR. cFunc == "AVG" .OR. ;
        cFunc == "MIN" .OR. cFunc == "MAX" )
      RETURN SqlComputeAggSimple( aGR, nCol, cFunc )
   ENDIF

   IF lDistinct
      hSeen := { => }
   ENDIF
   FOR i := 1 TO Len( aGR )
      IF nCol > 0 .AND. nCol <= Len( aGR[ i ] )
         xVal := aGR[ i ][ nCol ]
      ELSEIF nCol == 0
         /* Complex expression (CASE, BIN, etc.) inside aggregate:
          * evaluate the expression tree against the current row data. */
         xVal := SqlEvalRowExpr( xArg, aFN, aGR[ i ] )
      ELSE
         xVal := NIL
      ENDIF
      IF xVal != NIL
         IF lDistinct
            cKey := SqlValToStr( xVal )
            IF hb_HHasKey( hSeen, cKey )
               LOOP
            ENDIF
            hSeen[ cKey ] := .T.
         ENDIF
         nCount++
         nSum += SqlCoerceNum( xVal )
         /* Use SqlCmpLt for type-safe comparison (handles strings, dates) */
         IF xMin == NIL .OR. SqlCmpLt( xVal, xMin )
            xMin := xVal
         ENDIF
         IF xMax == NIL .OR. SqlCmpLt( xMax, xVal )
            xMax := xVal
         ENDIF
      ENDIF
   NEXT

   DO CASE
   CASE cFunc == "COUNT"
      RETURN nCount
   CASE cFunc == "SUM"
      /* SQL standard: SUM of all NULLs = NULL, not 0 */
      RETURN iif( nCount > 0, nSum, NIL )
   CASE cFunc == "AVG"
      RETURN iif( nCount > 0, nSum / nCount, NIL )
   CASE cFunc == "MIN"
      RETURN xMin
   CASE cFunc == "MAX"
      RETURN xMax
   CASE cFunc == "GROUP_CONCAT" .OR. cFunc == "STRING_AGG"
      cResult := ""
      cSep := ", "
      FOR i := 1 TO Len( aGR )
         IF nCol > 0 .AND. nCol <= Len( aGR[ i ] )
            xVal := aGR[ i ][ nCol ]
         ELSEIF nCol == 0
            xVal := SqlEvalRowExpr( xArg, aFN, aGR[ i ] )
         ELSE
            xVal := NIL
         ENDIF
         IF xVal != NIL
            IF ! Empty( cResult )
               cResult += cSep
            ENDIF
            cResult += SqlCoerceStr( xVal )
         ENDIF
      NEXT
      RETURN cResult
   ENDCASE

RETURN 0


METHOD EvalHaving( xHaving, aNewRow, aCols, aGroupRows, aFN, aParams ) CLASS TSqlAgg

   LOCAL xResult, aGo

   /* Fast path: Go-native tree walker. Returns {lOk, lPass}; falls back
    * to PRG when it hits an unsupported node (subqueries, complex agg
    * args, CASE expressions inside HAVING, etc.). */
   aGo := SqlEvalHaving( xHaving, aNewRow, aCols, aGroupRows, aFN, aParams )
   IF ValType( aGo ) == "A" .AND. Len( aGo ) == 2 .AND. aGo[ 1 ]
      RETURN aGo[ 2 ]
   ENDIF

   xResult := ::EvalHavingExpr( xHaving, aNewRow, aCols, aGroupRows, aFN, aParams )

RETURN SqlIsTrue( xResult )


METHOD EvalHavingExpr( xE, aNewRow, aCols, aGR, aFN, aParams ) CLASS TSqlAgg

   LOCAL xL, xR, cOp, i, nCI, cN

   IF xE == NIL
      RETURN NIL
   ENDIF

   DO CASE
   CASE xE[ 1 ] == ND_LIT
      RETURN xE[ 2 ]

   CASE xE[ 1 ] == ND_NIL
      RETURN NIL

   CASE xE[ 1 ] == ND_COL
      cN := xE[ 2 ]
      IF "." $ cN
         cN := SubStr( cN, At( ".", cN ) + 1 )
      ENDIF
      FOR i := 1 TO Len( aCols )
         IF Upper( aCols[ i ][ 2 ] ) == Upper( cN ) .AND. i <= Len( aNewRow )
            RETURN aNewRow[ i ]
         ENDIF
      NEXT
      nCI := ::FindColIdx2( cN, aFN )
      IF nCI > 0 .AND. Len( aGR ) > 0 .AND. nCI <= Len( aGR[ 1 ] )
         RETURN aGR[ 1 ][ nCI ]
      ENDIF
      RETURN NIL

   CASE xE[ 1 ] == ND_FN
      IF SqlIsAggName( xE[ 2 ] )
         RETURN ::ComputeAgg( xE, aGR, aFN )
      ENDIF
      RETURN NIL

   CASE xE[ 1 ] == ND_BIN
      cOp := xE[ 2 ]
      IF cOp == "AND"
         xL := ::EvalHavingExpr( xE[ 3 ], aNewRow, aCols, aGR, aFN, aParams )
         xR := ::EvalHavingExpr( xE[ 4 ], aNewRow, aCols, aGR, aFN, aParams )
         RETURN SqlIsTrue( xL ) .AND. SqlIsTrue( xR )
      ENDIF
      IF cOp == "OR"
         xL := ::EvalHavingExpr( xE[ 3 ], aNewRow, aCols, aGR, aFN, aParams )
         xR := ::EvalHavingExpr( xE[ 4 ], aNewRow, aCols, aGR, aFN, aParams )
         RETURN SqlIsTrue( xL ) .OR. SqlIsTrue( xR )
      ENDIF
      xL := ::EvalHavingExpr( xE[ 3 ], aNewRow, aCols, aGR, aFN, aParams )
      xR := ::EvalHavingExpr( xE[ 4 ], aNewRow, aCols, aGR, aFN, aParams )
      xL := SqlCoerceForCmp( xL )
      xR := SqlCoerceForCmp( xR )
      IF cOp == "=" .OR. cOp == "=="
         RETURN SqlCmpEq( xL, xR )
      ENDIF
      IF cOp == "<>" .OR. cOp == "!="
         RETURN ! SqlCmpEq( xL, xR )
      ENDIF
      IF cOp == ">"
         RETURN SqlCmpLt( xR, xL )
      ENDIF
      IF cOp == "<"
         RETURN SqlCmpLt( xL, xR )
      ENDIF
      IF cOp == ">="
         RETURN SqlCmpEq( xL, xR ) .OR. SqlCmpLt( xR, xL )
      ENDIF
      IF cOp == "<="
         RETURN SqlCmpEq( xL, xR ) .OR. SqlCmpLt( xL, xR )
      ENDIF
      /* Arithmetic inside HAVING: `HAVING SUM(amt)+1 > 200`,
       * `HAVING COUNT(*)*100 > 250`, etc. Without these branches
       * the wrapped expression returned NIL and the comparison
       * with the constant collapsed to false → 0 rows silent.
       * SQL NULL propagation: any NIL operand → NIL. */
      IF cOp == "+"
         IF xL == NIL .OR. xR == NIL
            RETURN NIL
         ENDIF
         IF ValType( xL ) == "D" .AND. ValType( xR ) == "N"
            RETURN xL + xR
         ENDIF
         IF ValType( xL ) == "N" .AND. ValType( xR ) == "D"
            RETURN xR + xL
         ENDIF
         RETURN SqlCoerceNum( xL ) + SqlCoerceNum( xR )
      ENDIF
      IF cOp == "-"
         IF xL == NIL .OR. xR == NIL
            RETURN NIL
         ENDIF
         IF ValType( xL ) == "D" .AND. ValType( xR ) == "N"
            RETURN xL - xR
         ENDIF
         IF ValType( xL ) == "D" .AND. ValType( xR ) == "D"
            RETURN xL - xR
         ENDIF
         RETURN SqlCoerceNum( xL ) - SqlCoerceNum( xR )
      ENDIF
      IF cOp == "*"
         IF xL == NIL .OR. xR == NIL
            RETURN NIL
         ENDIF
         RETURN SqlCoerceNum( xL ) * SqlCoerceNum( xR )
      ENDIF
      IF cOp == "/"
         IF xL == NIL .OR. xR == NIL
            RETURN NIL
         ENDIF
         IF SqlCoerceNum( xR ) != 0
            RETURN SqlCoerceNum( xL ) / SqlCoerceNum( xR )
         ENDIF
         RETURN NIL
      ENDIF
      IF cOp == "||"
         IF xL == NIL .OR. xR == NIL
            RETURN NIL
         ENDIF
         RETURN SqlCoerceStr( xL ) + SqlCoerceStr( xR )
      ENDIF
      RETURN NIL

   CASE xE[ 1 ] == ND_UNI
      IF xE[ 2 ] == "NOT"
         xL := ::EvalHavingExpr( xE[ 3 ], aNewRow, aCols, aGR, aFN, aParams )
         RETURN ! SqlIsTrue( xL )
      ENDIF
      RETURN NIL

   ENDCASE

RETURN NIL