Create an account
A database language enables the user to create database and table structures to perform basic data management chores.
A database language enables the user to perform complex queries designed to transform the raw data into useful information.
SQL is considered difficult to learn; its command set has a vocabulary of more than 300 words.
Entity integrity is enforced automatically when the primary key is specified in the CREATE TABLE command sequence.
The CHECK constraint is used to define a condition for the values that the attribute domain cannot have.
Any changes made to the contents of a table are not physically saved on disk until you use the SAVE <table name> command.
The COMMIT command does not permanently save all changes. In order to do that, you must use SAVE.
If you have not yet used the COMMIT command to store the changes permanently in the database, you can restore the database to its previous condition with the ROLLBACK command.
Although SQL commands can be grouped together on a single line, complex command sequences are best shown on separate lines, with space between the SQL command and the command's components.
You can select partial table contents by naming the desired fields and by placing restrictions on the rows to be included in the output.
Since computers identify all characters by their numeric codes, mathematical operators cannot be used to place restrictions on character-based attributes.
Some RDBMSs, such as Microsoft Access, automatically make the necessary conversions to eliminate case sensitivity.
The COUNT function is designed to tally the number of non-null "values" of an attribute, and is often used in conjunction with the DISTINCT clause.
To join tables, simply enumerate the tables in the FROM clause of the SELECT statement. The DBMS will create a Cartesian product of every table in the FROM clause. To get the correct results, you need to select the rows in which the common attribute values do not match.
Please allow access to your computer’s microphone to use Voice Recording.
Having trouble? Click here for help.
We can’t access your microphone!
Click the icon above to update your browser permissions and try again
Reload the page to try again!Reload
Press Cmd-0 to reset your zoom
Press Ctrl-0 to reset your zoom
It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.
Please upgrade Flash or install Chrome
to use Voice Recording.
For more help, see our troubleshooting page.
Your microphone is muted
For help fixing this issue, see this FAQ.
Star this term
You can study starred terms together