HP 3000 Manuals HP 3000 Manuals
At a Glance [REV BEG] Data access includes all the methods you use to access the data in source tables or files. These methods can be one or more of the following:[REV END] * adding tables * joining or merging tables * defining relations * deciding on which items to use in the final report * tuning the data access [REV BEG] At the simplest level, you access one data source and use all the items in the final report. But you can also choose more than one data source, join or merge data sources, and define access tables for the report that consist of joined or merged data sources. Once defined, access tables can appear as source tables in subsequent access tables for that report. (Access tables do not exist as logical files outside of the report specification.) When you join tables, you combine them in such as way that each record in the resulting access table can have a value for every item in the original tables. When you join two or more source tables, you must define a relation between the records in each table, based on a common item.[REV END] When you merge tables, you append the records of additional tables to the end of the records for the first table. There does not need to be any relationship between the tables merged. That is, there does not need to be a common relation item. You may not want to use all the combined items that result from a join or a merge. Selecting only the items that are necessary in your report is an optional part of defining data access. To access the data in the most efficient (that is, time-effective) way, you can use methods that will effectively tune your data access. This chapter covers * joins and relations * merged tables * data from different sources * items * precision of numbers * data access methods * relation conditions