concept of DB terms

[joonstar]

(1) I made a table in a test database.
(2) The name of table is table1.
(3) The table has two "filed".
(4) The name of the first field is "name".
(5) The name of the second field is "age".
(6) The table has two records.
(7) The first record is (Tom, 22).
(8) The second records has (Mary, 20).


Above is the description of my actual work today morning.
Did I use correct terms on the correct places in (1) ~ (8) sentences?

When I make table, what is the difference between "not null" and "null" ?

[raf]

Not sure what you're asking about the descriptions??

A database has tables. A table has columns/variabels/controls . A variable defines one feature of an record/observation. A field is the combinations of an record and a column. So if a table has 10 columns, there will be 10 fields in teh table for each record. Each record can have a value for each column.

Difference between Null and Not Null.
Null means this column can contain empty fields ("system missing" values). If for insance a user logs in and you create a new record in a table that has an variable that registers the time a user loggs out , this field can initially stay empry. If you dont insert a value when the record is created, it has no value, or Null (this is not the same as 0 or 'null', which are values)

[joonstar]

Now I understand clearly what is "Null" and "Not Null".

I am still in doubt about other terms.
I might have to study more.

Thank you.