Here is a solution.

Access 2.0 does not support OUTERJOIN yet, so I jury-rigged an
outer join via a UNION, two LEFT JOINS, and a JOIN.

First, I put your data into two tables:

temperature(id, temp)
ph(id, pH)

notation is: <table name>(<field name>, <field name>, ...).

Using these schemas, I put your data in, giving

temperature: 
id	temp
100001	26.0
278128	27.0
100003	24.5
314159	29.0

ph:
id	pH
100001	7.4
100004	7.7
100003	7.6
314159	7.5

For purposes of this example, I used text fields everywhere
with no indexes or  primary keys.  For efficiency, you would want
to index on id and use numeric fields.   Everything  would still
work as below with no modifications.

The following queries provide a solution.  You can cut and
paste these directly into Access defining new queries having the
names and query definitions exactly as shown.  For each query,
create a new blank query, containing no tables.  Go into the
SQL Window, where you will see "SELECT DISTINCTROW;", which you
should replace by the <query body> from below.  Then save the
query as <query name> from below.

Notation below is:
<query name>:
<query body>

qyUNIONid:
SELECT id FROM temperature
UNION
SELECT id FROM ph;

qyUNIONid_LJOIN_ph:
SELECT qyUNIONid.id, ph.pH
   FROM qyUNIONid LEFT JOIN ph
        ON qyUNIONid.id = ph.id;

qyUNIONid_LJOIN_temperature:
SELECT qyUNIONid.id, temperature.temp
  FROM qyUNIONid LEFT JOIN temperature
       ON qyUNIONid.id = temperature.id;

qyOUTERJOINexample:
SELECT qyUNIONid_LJOIN_temperature.id, temp, pH
   FROM qyUNIONid_LJOIN_temperature INNER JOIN qyUNIONid_LJOIN_ph
        ON qyUNIONid_LJOIN_temperature.id = qyUNIONid_LJOIN_ph.id;


Open qyOUTERJOINexample and you'll see:

id      temp    pH
100001  26.0    7.4
100003  24.5    7.6
100004          7.7
278128  27.0    
314159  29.0    7.5


Dennis G. Allard
Ocean Park Software
tel. (usa) 310.399.4740
internet: allard@oceanpark.com