Structure of Expressions
An expression consists of any combination of column names, literals, operators, or functions.
Follow these guidelines in combining elements to form expressions:
Reference columns by typing their names. If your query uses more than one table and if you use a column name that is not unique, you must add the table name and a period to the column name. The following example shows the column name job_id qualified with the table name employee:
employee.job_idInclude literal text by enclosing it in single quotation marks; no quotation marks are necessary for numbers.
Note
In some databases, terms in single quotation marks are interpreted as literal values whereas terms in double quotation marks are interpreted as database objects such as column or table references. Therefore, the Query and View Designer can accept terms in double quotation marks, but might interpret them differently than you expect. In SQL Server, the Query and View Designer always interprets double quotation marks as database object delimiters.
Use standard arithmetic operators for numbers and a concatenation operator for combining strings.
Include parentheses to establish precedence of operators.
If you include a function, use these same guidelines for the arguments passed to the function. That is, reference columns by typing their names, enclose literal text in single quotation marks, and so on.
If you pass column names as function arguments, be sure the data type of the column is appropriate for the function argument.
You can include user-defined functions returning a scalar value in an expression.
The following table illustrates the use of expressions in a query.
Expression* |
Result |
|---|---|
SELECT (price * .9)FROM products |
Displays a discounted price (10% off the value in the price column). |
SELECT sales.qty, titles.price FROM sales INNER JOIN titles ON sales.title_id = titles.title_id ORDER BY (sales.qty * titles.price) |
After joining two tables, sorts the result set by the total value of an order (quantity multiplied by price). |
SELECT au_lname, au_fname FROM authors WHERE (SUBSTRING(phone, 1, 3) = '415') |
Displays authors whose area code is in the San Francisco area. |
SELECT ord_num, ord_date FROM sales WHERE (ord_date >= DATEADD(day, -10, GETDATE())) |
Finds all orders in the sales table that were made in the last 10 days. Today's date is returned by the GETDATE( ) function. |
* Some of the operators and functions shown here are specific to one database. For details about what operators and functions you can use, refer to the documentation for your database.
See Also
Concepts
Predefined Variables for Expressions