Structure of Expressions

General guidelines for creating 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_id
```
Include literal text by enclosing it in single quotation marks; no quotation marks are necessary for numbers.
Note The Query Designer can accept terms in double quotation marks, but might interpret them differently than you expect. In a Microsoft Access Project, the Query 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.

Expression examples

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 (lname + ', ' + fname) FROM employee`	Displays the concatenated values of the last name and first name columns with a comma between them.
`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 times 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.