SQLite

    case TK_INTEGER:
    case TK_STRING:
    case TK_FLOAT:
    case TK_BLOB:
      return 0;
    case TK_COLUMN:
      assert( p->pTab!=0 );
      return ExprHasProperty(p, EP_CanBeNull) ||
             (p->iColumn>=0 && p->pTab->aCol[p->iColumn].notNull==0);
    default:
      return 1;
  }
}

/*
** Return TRUE if the given expression is a constant which would be

            break;
          }
        }
      }
      if( pMatch ){
        pExpr->iTable = pMatch->iCursor;
        pExpr->pTab = pMatch->pTab;
        assert( (pMatch->jointype & JT_RIGHT)==0 ); /* RIGHT JOIN not (yet) supported */
        if( (pMatch->jointype & JT_LEFT)!=0 ){
          ExprSetProperty(pExpr, EP_CanBeNull);
        }
        pSchema = pExpr->pTab->pSchema;
      }
    } /* if( pSrcList ) */

#ifndef SQLITE_OMIT_TRIGGER
    /* If we have not already resolved the name, then maybe 
    ** it is a new.* or old.* trigger argument reference

  AggInfo *pAggInfo;     /* Used by TK_AGG_COLUMN and TK_AGG_FUNCTION */
  Table *pTab;           /* Table for TK_COLUMN expressions. */
};

/*
** The following are the meanings of bits in the Expr.flags field.
*/
#define EP_FromJoin  0x000001 /* Originates in ON/USING clause of outer join */
#define EP_Agg       0x000002 /* Contains one or more aggregate functions */
#define EP_Resolved  0x000004 /* IDs have been resolved to COLUMNs */
#define EP_Error     0x000008 /* Expression contains one or more errors */
#define EP_Distinct  0x000010 /* Aggregate function with DISTINCT keyword */
#define EP_VarSelect 0x000020 /* pSelect is correlated, not constant */
#define EP_DblQuoted 0x000040 /* token.z was originally in "..." */
#define EP_InfixFunc 0x000080 /* True for an infix function: LIKE, GLOB, etc */
#define EP_Collate   0x000100 /* Tree contains a TK_COLLATE operator */
#define EP_Generic   0x000200 /* Ignore COLLATE or affinity on this tree */
#define EP_IntValue  0x000400 /* Integer value contained in u.iValue */
#define EP_xIsSelect 0x000800 /* x.pSelect is valid (otherwise x.pList is) */
#define EP_Skip      0x001000 /* COLLATE, AS, or UNLIKELY */
#define EP_Reduced   0x002000 /* Expr struct EXPR_REDUCEDSIZE bytes only */
#define EP_TokenOnly 0x004000 /* Expr struct EXPR_TOKENONLYSIZE bytes only */
#define EP_Static    0x008000 /* Held in memory not obtained from malloc() */
#define EP_MemToken  0x010000 /* Need to sqlite3DbFree() Expr.zToken */
#define EP_NoReduce  0x020000 /* Cannot EXPRDUP_REDUCE this Expr */
#define EP_Unlikely  0x040000 /* unlikely() or likelihood() function */
#define EP_Constant  0x080000 /* Node is a constant */
#define EP_CanBeNull 0x100000 /* Can be null despite NOT NULL constraint */

/*
** These macros can be used to test, set, or clear bits in the 
** Expr.flags field.
*/
#define ExprHasProperty(E,P)     (((E)->flags&(P))!=0)
#define ExprHasAllProperty(E,P)  (((E)->flags&(P))==(P))

do_test join5-2.11 {
  execsql {SELECT * FROM xy LEFT JOIN ab ON 1 WHERE NULL}
} {}
do_test join5-2.12 {
  execsql {SELECT * FROM xy LEFT JOIN ab ON NULL WHERE NULL}
} {}

# Ticket https://www.sqlite.org/src/tktview/6f2222d550f5b0ee7ed37601
# Incorrect output on a LEFT JOIN.
#
do_execsql_test join5-3.1 {
  DROP TABLE IF EXISTS t1;
  DROP TABLE IF EXISTS t2;
  DROP TABLE IF EXISTS t3;
  CREATE TABLE x1(a);
  INSERT INTO x1 VALUES(1);
  CREATE TABLE x2(b NOT NULL);
  CREATE TABLE x3(c, d);
  INSERT INTO x3 VALUES('a', NULL);
  INSERT INTO x3 VALUES('b', NULL);
  INSERT INTO x3 VALUES('c', NULL);
  SELECT * FROM x1 LEFT JOIN x2 LEFT JOIN x3 ON x3.d = x2.b;
} {1 {} {} {}}
do_execsql_test join5-3.2 {
  DROP TABLE IF EXISTS t1;
  DROP TABLE IF EXISTS t2;
  DROP TABLE IF EXISTS t3;
  DROP TABLE IF EXISTS t4;
  DROP TABLE IF EXISTS t5;
  CREATE TABLE t1(x text NOT NULL, y text);
  CREATE TABLE t2(u text NOT NULL, x text NOT NULL);
  CREATE TABLE t3(w text NOT NULL, v text);
  CREATE TABLE t4(w text NOT NULL, z text NOT NULL);
  CREATE TABLE t5(z text NOT NULL, m text);
  INSERT INTO t1 VALUES('f6d7661f-4efe-4c90-87b5-858e61cd178b',NULL);
  INSERT INTO t1 VALUES('f6ea82c3-2cad-45ce-ae8f-3ddca4fb2f48',NULL);
  INSERT INTO t1 VALUES('f6f47499-ecb4-474b-9a02-35be73c235e5',NULL);
  INSERT INTO t1 VALUES('56f47499-ecb4-474b-9a02-35be73c235e5',NULL);
  INSERT INTO t3 VALUES('007f2033-cb20-494c-b135-a1e4eb66130c',
                        'f6d7661f-4efe-4c90-87b5-858e61cd178b');
  SELECT *
    FROM t3
         INNER JOIN t1 ON t1.x= t3.v AND t1.y IS NULL
         LEFT JOIN t4  ON t4.w = t3.w
         LEFT JOIN t5  ON t5.z = t4.z
         LEFT JOIN t2  ON t2.u = t5.m
         LEFT JOIN t1 xyz ON xyz.y = t2.x;
} {007f2033-cb20-494c-b135-a1e4eb66130c f6d7661f-4efe-4c90-87b5-858e61cd178b f6d7661f-4efe-4c90-87b5-858e61cd178b {} {} {} {} {} {} {} {} {}}
do_execsql_test join5-3.3 {
  DROP TABLE IF EXISTS x1;
  DROP TABLE IF EXISTS x2;
  DROP TABLE IF EXISTS x3;
  CREATE TABLE x1(a);
  INSERT INTO x1 VALUES(1);
  CREATE TABLE x2(b NOT NULL);
  CREATE TABLE x3(c, d);
  INSERT INTO x3 VALUES('a', NULL);
  INSERT INTO x3 VALUES('b', NULL);
  INSERT INTO x3 VALUES('c', NULL);
  SELECT * FROM x1 LEFT JOIN x2 JOIN x3 WHERE x3.d = x2.b;
} {}

finish_test