Using Parameters

What is a Parameter?

Parameter is a placeholder for a variable that contains a value of some type that is passed to a database server along with the SQL text at the query execution time. Also parameter can hold values returned by a server after query or stored procedure execution.

You can benefit from using of parameters in the following situations:

  • When you execute a query multiple times with different input values

  • When you debug a query from your application code

Adding Parameters to a Query Text

There are two types of parameters, that you can add to a query text:

  • Named parameter

  • Unnamed parameter

Named Parameters

Parameters are declared using ’:’ prefix followed by name of the parameter.

For example:

SELECT
  employee.*
FROM
  hr.employee
WHERE
  employee.title = :job AND
  employee.vacation_hours <= :level

:job and :level are parameters in this query.

Unnamed Parameters

Unnamed parameters can be specified as ’?’ or $ symbol.

For example:

SELECT
  employee.*
FROM
  hr.employee
WHERE
  employee.title = ? AND
  employee.vacation_hours <= ?

Parameters for this query are created in the order of appearance.

Modifying Parameter Values and Types

When you run a query that contains parameters with empty values, you will be automatically prompted to initialize them.

To set parameter values and types select Edit Parameters command from SQL toolbar or main menu. In open Edit Parameters dialog box set parameters’ type, value, and other properties.