This page is for anyone who needs to embed expressions within wider statements.

Overview

To embed an expression within a statement or text:

1. Prefix with $
2. Enclose the expression within curly brackets

${ … }

For example, you can use expressions within the text of an email to include details specific to each recipient.

Embedded expressions are evaluated at run-time and the results are:

• either inserted back into the outer statement
• or retained as separate parameters according to the rules of the language (text, SQL, XML, JSON); see Statement Language Rules, below.

The variables that you can reference in embedded expressions depend on context.

Statement Language Rules 

The rules for embedding expressions depend on the language of the statement.

Text, XML and HTML

${…} is the recommended syntax, although the $ can be omited.

${…} expressions are ignored when they are inside:

• single quotes
• double quotes 
• ‘--’ comments.

If the first character of the embedded expression is an equals sign =, this character is ignored.

The embedded expression is ended by the first closing curly bracket }, regardless of the content of the expression.

The result of evaluating the expression is inserted into the statement.

SQL

${…} is the recommended syntax, although the $ can be omited.

${…} expressions are ignored when they are inside:

• single quotes
• double quotes 
• ‘--’ comments.

The embedded expression is ended by the first closing curly bracket }, regardless of the content of the expression.

How the result of the evaluating the expression is used depends on the first character of the embedded expression. Where the first character:

• is an equals sign =, it is stripped before the expression is evaluated. The result of evaluating the expression is inserted as text into the statement.
  This is how to pass a variable representing a table name and then insert something into the table.
• is not an equals sign, the result of evaluating the expression is passed as a separate parameter to the JDBC driver.
  This is how to pass values to be inserted into a table row.

JSON

${…} is the required syntax. JSON uses curly brackets, so the $ acts as an escape character.

${…} expressions are recognised in a statement even when they are inside:

• single quotes
• double quotes.

The embedded expression is ended by the first closing curly bracket } that it is outside any single / double quote pairs within the expression.

$$ escapes a single $ in the statement, without marking the start of an embedded expression.

The result of evaluating the expressions is inserted into the statement as text.