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 General Information 

If you want to evaluate system tables, note the following information:

·        When system tables are evaluated, the system only outputs information for objects of which the current user is the owner, or for which the user has at least a privilege (the user therefore knows the object). This authorization concept may mean that the table definition visible for the current user differs from the actual definition.
The definition of a view table is only visible for the owner of the view table.

·        When you query the system table(s), you should enter conditions that describe the required object as precisely as possible. Entering the object owner considerably speeds up the search for the relevant information.

·        When you specify search commands, you should specify equivalence conditions where possible. Specifying LIKE conditions is less effective.

·        For performance reasons, when you query information from system tables, you should use not only the SQL statement SELECT * but also limit the number of output columns to those columns that you actually require.
When you query statistical information from system tables, in particular, additional actions are performed to determine column values in the database system when certain output columns are requested. As a result, you should only have the system determine this column information if you really need it.

·        Simple identifiers are always created in the database instance in capital letters, regardless of how they were entered during definition of the data.
If you use simple identifiers in a search condition, you must enter the single quotes typically used when specifying literals.
For performance reasons, you should not leave the conversion of the simple identifier to capital letters to the database system at the execution of the SQL statement; you should enter the simple identifier directly in capital letters in the search condition.

CREATE TABLE mytab (…)
SELECT … FROM … WHERE … = 'MYTAB'

·        Special identifiers are always specified in double quotes in the data definition. In the database instance, these are stored as they were entered, meaning they are not converted to capital letters.
If you use special identifiers in a search condition, you must enter the single quotes typical for specifying literals.

CREATE TABLE "this is mytab" (…)
SELECT … FROM … WHERE … = 'this is mytab'

 

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