What is a dual table?

Dual table is a special table exclusive for Oracle® databases that have only one column and one row, so there is only one piece of data. The main reason for the dual table is comfort because it makes it easier to encode certain database functions. Unlike other tables in the database to be modified and changed, the dual part should not be changed. If this part changes at all, terrible errors may occur and the entire database can eventually be damaged. The dual section is primarily used in conjunction with the pseudo columns and calculations that need a table. By default, the column is called the mannequin and the value contained in the cell is x, which is useful for calculations based on X. SYS, abbreviation for the "system", is the owner of a dual cell. All sys data should be left alone and unchanged.

users are able to change the dual table with several simple formulas and can insert their own information into the cell. Although it can be done, it should not be and should never be. PokUD The default X turns into anything else, catastrophic problems may appear in the database, including data corruption. This is because the dual is used automatically in some samples and if the X is different, a damaged code will be introduced into the database.

In many questions of database or samples, clause and from is required. Normally, when this clause is used in a database for a query, a table must be entered. The table is where the calculation is carried out or where the information comes from, and therefore it is necessary in most common functions. If the calculation is not necessary or is not needed or is not necessary, a dual table can be entered. This allows you to work without introducing the table.

Along with questions offers a dual table with another advantage. Less coding is required to use the dual part, and while encoding is mild, a larger database will see improved performance. With less queries encoding, the database will be able to work faster. It is also useful in calculations that have consistent integers and those that can use the workZdné x integer without required to change the cell.