SQLite

  pAggInfo = pExpr->pAggInfo;
  if( pExpr->iAgg>=pAggInfo->nColumn ) return WRC_Continue;
  assert( pExpr->iAgg>=0 );
  pCol = &pAggInfo->aCol[pExpr->iAgg];
  pExpr->op = TK_AGG_COLUMN;
  pExpr->iTable = pCol->iTable;
  pExpr->iColumn = pCol->iColumn;
  ExprClearProperty(pExpr, EP_Skip|EP_Collate);
  return WRC_Prune;
}

/*
** Convert every pAggInfo->aFunc[].pExpr such that any node within
** those expressions that has pAppInfo set is changed into a TK_AGG_COLUMN
** opcode.

  CREATE TABLE t2(c INT, d INT);
  INSERT INTO t1(a,b) VALUES(4,4),(5,-5),(5,20),(6,6);
  INSERT INTO t2(c,d) VALUES(100,1),(200,1),(300,2);
  SELECT *,
    (SELECT max(c+abs(b)) FROM t2 GROUP BY d ORDER BY d LIMIT 1) AS subq
   FROM t1 WHERE a=5;
} {5 -5 205 5 20 220}

# 2023-04-03 https://sqlite.org/forum/forumpost/44270909bb
# and https://sqlite.org/forum/forumpost/e45108732c which are the
# same problem, namely the failure to omit the EP_Collate property
# from an expression node when changing it from TK_COLLATE into
# TK_AGG_COLUMN because it resolves to an indexed expression.
#
reset_db
do_execsql_test 10.0 {
  CREATE TABLE t1(a INTEGER PRIMARY KEY, b TEXT);
  CREATE INDEX t1x ON t1 (b, +b COLLATE NOCASE);
  INSERT INTO t1(a,b) VALUES(1,'abcde');
  SELECT * FROM t1 AS a0
   WHERE (SELECT count(a0.b=+a0.b COLLATE NOCASE IN (b)) FROM t1 GROUP BY 2.5)
   ORDER BY a0.b;
} {1 abcde}
do_execsql_test 10.1 {
  CREATE TABLE t2(a TEXT);
  INSERT INTO t2 VALUES('alice'),('bob'),('cindy'),('david');
  CREATE INDEX t2x ON t2 (+a COLLATE NOCASE);
  SELECT count(+a COLLATE NOCASE IN (SELECT 1)) AS x
    FROM t2
   GROUP BY SUBSTR(0,0);
} 4

finish_test