querytips.txt

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Query Tips
 
- Cheetah automatically formats a numeric string (used with fields of type N) to the correct size and 
number of decimal places when the query is compiled. There is no need for the programmer to predefine
the numeric length and right justify the numeric string with the correct number of decimal places.

- Queries on character strings (other than numeric) should be defined at the proper length when
creating the query. If the string is not the same size as the field length then the string is
automatically left aligned in a string of the proper length.

- Can specify up to 50 conditions by using the xdbQueryCondition function. You can join each condition
with equates %QUERY_AND, %QUERY_OR. The first condition must always have a join phrase equal to zero.

- You can also specify special conditions (as part of the 50 conditions) to keep track of aggregate amounts
related to the query result set. These functions are %SUM, %MINIMUM, %MAXIMUM, %AVERAGE. When the query
is created, you call functions to determine what the aggregate amounts are. These functions are xdbQuerySUM#,
xdbQueryMIN#, xdbQueryMAX#, and xdbQueryAVG#.

- You should note that every condition you add to a query will slow down the processing of the query a
little bit. Only use conditions that are necessary to accomplish what you need. Do not overuse the %SUM,
%MINIMUM, %MAXIMIM, or %AVERAGE conditions unless you really need them.

- The query module will automatically create a temporary query file if the size of the resultant query set
is too big to fit in the allocated memory for a query node. Current the node size is 4K. This will allow for
results with as many as 1024 records (i.e. 4096 / 4). Actually, the number of records is one less (i.e. 1023)
because Cheetah uses the first 4 bytes of the node to hold the amount of records contained in the node. If a
temporary disk file is created then it is automatically erased with the query is destroyed (i.e. xdbDestroyQuery).