不需要根据ID等唯一标识符去查找，只要一条sql语句要求返回所有的患者。
Instead of finding by a unique identifier like id, an SQL statement requests that all patients be returned.
例如你要写一句赋值语句，你可以声明任何类型的变量，在等号的左边使用任何标识符，然后在右边给出任何的表达式。
In writing an assignment statement, for example, you can declare variables of any type, use any identifier to the left of the equal sign, and supply any expression on the right.
行标识符(RID_BIT或RID)内置函数：该内置函数可用于SELECT列表或谓词语句。
Row identifier (RID_BIT or RID) built-in function: This built-in function can be used in the SELECT list or predicates statement.
当您为select语句调用odbc_exec函数时，该函数返回一个结果集标识符。
When you call the odbc_exec function for a SELECT statement, the function returns a result set identifier.
标识符是在赋值语句中进行定义和初始化的，并且可以在任何允许使用的地方使用。
An identifier is defined and initialized in an assignment and can be used anywhere a value is allowed. Listing 3 shows a sample grammar.
要在SQL语句中使用保留字作为标识符，必须用双引号将它引起来。
To use a reserved word in a SQL statement as an identifier, you must enclose it in double quotes.
要在SQL语句中使用保留字作为标识符，必须用双引号将它引起来。
To use a reserved word in a SQL statement as an identifier, you must enclose it in double quotes.
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