SQLite

  if( ALWAYS(pExpr) && pExpr->op==TK_ID ){
    /* The value of a generated column needs to be a real expression, not
    ** just a reference to another column, in order for covering index
    ** optimizations to work correctly.  So if the value is not an expression,
    ** turn it into one by adding a unary "+" operator. */
    pExpr = sqlite3PExpr(pParse, TK_UPLUS, pExpr, 0);
  }
  pExpr->affExpr = pCol->affinity;
  sqlite3ColumnSetExpr(pParse, pTab, pCol, pExpr);
  pExpr = 0;
  goto generated_done;

generated_error:
  sqlite3ErrorMsg(pParse, "error in generated column \"%s\"",
                  pCol->zCnName);

  Parse *pParse,   /* The parsing context */
  Expr *pExpr,     /* The expression to potentially bypass */
  int target       /* Where to store the result of the expression */
){
  IndexedExpr *p;
  Vdbe *v;
  for(p=pParse->pIdxEpr; p; p=p->pIENext){
    u8 exprAff;
    int iDataCur = p->iDataCur;
    if( iDataCur<0 ) continue;
    if( pParse->iSelfTab ){
      if( p->iDataCur!=pParse->iSelfTab-1 ) continue;
      iDataCur = -1;
    }
    if( sqlite3ExprCompare(0, pExpr, p->pExpr, iDataCur)!=0 ) continue;
    assert( p->aff>=SQLITE_AFF_BLOB && p->aff<=SQLITE_AFF_NUMERIC );
    exprAff = sqlite3ExprAffinity(pExpr);
    if( (exprAff<=SQLITE_AFF_BLOB && p->aff!=SQLITE_AFF_BLOB)
     || (exprAff==SQLITE_AFF_TEXT && p->aff!=SQLITE_AFF_TEXT)
     || (exprAff>=SQLITE_AFF_NUMERIC && p->aff!=SQLITE_AFF_NUMERIC)
    ){
      /* Affinity mismatch on a generated column */
      continue;
    }

    v = pParse->pVdbe;
    assert( v!=0 );
    if( p->bMaybeNullRow ){
      /* If the index is on a NULL row due to an outer join, then we
      ** cannot extract the value from the index.  The value must be
      ** computed using the original expression. */
      int addr = sqlite3VdbeCurrentAddr(v);

*/
struct IndexedExpr {
  Expr *pExpr;            /* The expression contained in the index */
  int iDataCur;           /* The data cursor associated with the index */
  int iIdxCur;            /* The index cursor */
  int iIdxCol;            /* The index column that contains value of pExpr */
  u8 bMaybeNullRow;       /* True if we need an OP_IfNullRow check */
  u8 aff;                 /* Affinity of the pExpr expression */
  IndexedExpr *pIENext;   /* Next in a list of all indexed expressions */
#ifdef SQLITE_ENABLE_EXPLAIN_COMMENTS
  const char *zIdxName;   /* Name of index, used only for bytecode comments */
#endif
};

/*

    }
#endif
    p->pExpr = sqlite3ExprDup(pParse->db, pExpr, 0);
    p->iDataCur = pTabItem->iCursor;
    p->iIdxCur = iIdxCur;
    p->iIdxCol = i;
    p->bMaybeNullRow = bMaybeNullRow;
    if( sqlite3IndexAffinityStr(pParse->db, pIdx) ){
      p->aff = pIdx->zColAff[i];
    }
#ifdef SQLITE_ENABLE_EXPLAIN_COMMENTS
    p->zIdxName = pIdx->zName;
#endif
    pParse->pIdxEpr = p;
    if( p->pIENext==0 ){
      sqlite3ParserAddCleanup(pParse, whereIndexedExprCleanup, pParse);
    }

  CREATE TABLE t0(a PRIMARY KEY,b TEXT AS ('2') UNIQUE);
  INSERT INTO t0(a) VALUES(2);
  SELECT * FROM t0 AS x JOIN t0 AS y
   WHERE x.b='2'
     AND (y.a=2 OR (x.b LIKE '2*' AND y.a=x.b));
} {2 2 2 2}


# 2023-03-02 dbsqlfuzz 65f5eb57f8859344d5f1f33e08c77ee12960ed83
#
set typelist {ANY INT REAL BLOB TEXT {}}
set cnt 0
foreach t1 $typelist {
  foreach t2 $typelist {
    incr cnt
    db eval "
      DROP TABLE IF EXISTS t1;
      CREATE TABLE t1(
        x $t1,
        a $t2 AS (x) VIRTUAL,
        b BLOB AS (x) VIRTUAL
      );
      CREATE INDEX x2 ON t1(a);
      INSERT INTO t1(x) VALUES(NULL),('1'),(2),(3.5),('xyz');
    "
    set x1 [lsort [db eval {SELECT typeof(b) FROM t1}]]
    do_test gencol1-23.1.$cnt {
      lsort [db eval {SELECT typeof(b) FROM t1 INDEXED BY x2}]
    } $x1
  }
}
do_execsql_test gencol1-23.2 {
  DROP TABLE t1;
  CREATE TABLE t1(
    x,
    a INT AS (x) VIRTUAL,
    b BLOB AS (x) VIRTUAL
  );
  CREATE INDEX x2 ON t1(a);
  INSERT INTO t1(x) VALUES(NULL),('1'),('xyz'),(2),(3.5);
  SELECT quote(a) FROM t1 INDEXED BY x2;
} {NULL 1 2 3.5 'xyz'}
do_execsql_test gencol1-23.3 {
  EXPLAIN SELECT a FROM t1 INDEXED BY x2;
} {~/Column 0/}
#    ^^^^^^^^---- verfies that x2 acts like a covering index
do_execsql_test gencol1-23.4 {
  EXPLAIN SELECT b FROM t1 INDEXED BY x2;
} {/Column 0/}
#  ^^^^^^^^^^--- Must reference the original table in this case because
# of the different datatype on column b.

finish_test