4.3.1. Using Positional Notation
4.3.1.使用位置表示法
Positional notation is the traditional mechanism for passing arguments to functions in PostgreSQL.
An example is:
位置表示法是PostgreSQL为函数传参的传统机制。示例如下:
SELECT concat_lower_or_upper('Hello', 'World', true);
concat_lower_or_upper
-----------------------
HELLO WORLD
(1 row)
All arguments are specified in order. The result is upper case since
uppercase
is specified as
true
.
Another example is:
所有的参数都按序指定。因为uppercase指定为true,所以返回大写。另一个示例:
SELECT concat_lower_or_upper('Hello', 'World');
concat_lower_or_upper
-----------------------
hello world
(1 row)
Here, the
uppercase
parameter is omitted, so it receives its default value of
false
, resulting in
lower case output. In positional notation, arguments can be omitted from right to left so long as they
have defaults.
上例中,为指定uppercase参数值,所以为默认值false,因此返回的为小写。在位置表示法中,参数如果有默认值,则可以从右到左忽略。