Class for SQL SELECT fragments.
This class simply holds a string, so that fragments of SQL statements can be distinguished from identifiers and values that should be implicitly quoted when interpolated into SQL statements.
For example, when specifying a primary key value when inserting into a new row, some RDBMS brands may require you to use an expression to generate the new value of a sequence. If this expression is treated as an identifier, it will be quoted and the expression will not be evaluated. Another example is that you can use Zend_Db_Expr in the Zend_Db_Select::order() method to order by an expression instead of simply a column name.
The way this works is that in each context in which a column name can be specified to methods of Zend_Db classes, if the value is an instance of Zend_Db_Expr instead of a plain string, then the expression is not quoted. If it is a plain string, it is assumed to be a plain column name.
|copyright||Copyright (c) 2005-2015 Zend Technologies USA Inc. (http://www.zend.com)|
|license||New BSD License|
The string containing a SQL expression.
__toString() : string
stringThe string of the SQL expression stored in this object.
$_expression : string