Oracle's DUAL table is a very special "dummy" database table that is used for generating constant values as part of your SQL query.
- [Instructor] The dual table in Oracle…is a special table created during installation…of the Oracle database, and it's especially useful…when we want to retrieve constant literal strings…from the database without selecting…any actual database data…or experiment with certain SQL functions.…So for example, say that you want to return…the hello world string from an Oracle database.…Without specify a from clause…in your SQL statement,…unlike other database engines,…the following query will fail in Oracle…telling us that the from keyword was not found.…
Luckily for us, dual comes to the rescue.…Simply typing from dual…and running the query again…will return us the desired output.…We can also use dual in combination…of certain SQL functions.…So for example, I can type upper hello world…from dual,…and my query will return an uppercase value…for hello world.…The dual table itself contains a single row.…That's why when using dual…as part of SQL queries to select values…by default will return a single value.…
Note: This training course is appropriate for beginning database developers with no prior experience with SQL or Oracle.
- Using Oracle SQL*Developer, the free development environment
- Selecting data from tables
- Filtering data
- Using functions to manipulate data
- Joining data from tables
- Creating tables
- Updating values
- Truncating data
- Grouping and ordering result sets
- Working with primary keys
- Checking constraints
Skill Level Beginner
Oracle 12c Database: Administrationwith David Yahalom3h 58m Beginner
Database Foundations: Core Conceptswith Adam Wilbert2h 14m Beginner
Database Foundations: Administrationwith Adam Wilbert1h 14m Beginner
1. Introduction to SQL
2. Preparing the Course Environment
Downloading the course VM2m 16s
3. Using Oracle SQL Developer
4. Basic SELECT Queries
5. String, Number, and Date Functions
6. Joining Table Data
7. Manipulating Data
8. Grouping Data
9. Advanced Topics
Next steps1m 33s
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