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C H A P T E R 1 1
Data Storage and Retrieval
About Data Storage on Newton Devices
11-13
exclusive forms of the same endrange selector; for example, a single query spec
cannot specify both a
beginKey
value and a
beginExclKey
value.
Another important point to understand is that there is only one
beginKey
or
beginExclKey
value, and only one
endKey
or
endExclKey
value associated
with any query and the cursor it returns.
Figure 11-4
Using
beginExclKey
and
endExclKey
values to specify
a subrange
Each
beginKey
,
beginExclKey
,
endKey
, or
endExclKey
specification
evaluates to a single value that has a unique position in the sorted index key data.
This position marks one end of the range over which the cursor iterates. The cursor
never moves to a position outside the range specified by these keys.
If any endrange selectors are defined for a query, the relationship of the cursor's
entries to the endrange selectors may be summarized as follows:
entry
> beginExclKey
entry
beginKey
entry
endKey
entry
< endExclKey
You can think of these values as being used by the system in an inequality
expression to specify the range of the cursor; for example,
beginKey
entry
< endExclKey
Note that if a valid entry is not found at the key value specified for an endrange
selector, the cursor is positioned on the nearest entry in index key order that falls
within the range specified by the endrange selectors. For example, if a valid entry is
not found at the key value specified for a
beginKey
or
beginExclKey
value, the
Ascending key order
Descending key order
subrange of index key values
3 4 5
beginExclKey
endExclKey
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