The DUAL table in Oracle databases has one row and column, used for convenience in coding certain functions. It should not be altered, as it can cause errors and corruption. It is owned by SYS and changing the default X value can lead to catastrophic problems. It can be used in queries and calculations, requiring less coding and improving performance.
The DUAL table is a special table exclusive to Oracle® databases that has only one column and one row, so there is only one piece of data. The main reason for the DUAL table is convenience, because it makes it easier to code certain database functions. Unlike other tables in the database, which would need to be modified and changed, the DUAL section shouldn’t be altered. If this section is changed, terrible errors can occur and the entire database could be corrupted. The DUAL section is mainly used in combination with pseudo columns and calculations that require a table.
In DUAL table, there is only one row and one column, so it has only single piece of information. By default, the column is named DUMMY and the value contained within the cell is X, making it useful for X-based calculations. SYS, short for “system,” owns the DUAL cell. All SYS data should be left alone and unmodified.
Users are able to change the DUAL table information with a few simple formulas and can enter their own information into the cell. While this can be done, it is not meant to be and never should be. If the default X is changed to something else, catastrophic problems can occur with the database, including data corruption. This is because DUAL is automatically used in some formulas and if the X is different then corrupted code will be introduced into the database.
In many database queries or formulas, a FROM clause is required. Normally, when this clause is used in a database to query, a table must be specified. The table is where the calculation is done or where the information comes from, which is why it is needed in most normal functions. If a table is not needed or not required for the calculation, the DUAL table can be specified. This will allow the query to work without introducing a table.
Along with queries, the DUAL table offers another advantage. Less coding is required to use a DUAL section, and while the coding is lightweight, larger databases will see improved performance. With less query coding, your database will be able to run faster. It is also useful in calculations that have consistent integers and those that can use the entire empty X without requiring cell modification.
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