postgresql 如何在PostgreSQL中声明变量
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how to declare variable in PostgreSQL
提问by user307880
I try to declare a variable in a code like this, but it's doesn't work. Can you tell me what's the problem?
我尝试在这样的代码中声明一个变量，但它不起作用。你能告诉我有什么问题吗？
ERROR: syntax error at or near "VARCHAR"
LINE 2: p_country VARCHAR;
DECLARE
p_country VARCHAR;
p_country : = '';
SELECT p_country;
回答by Frank Heikens
Create a new setting in postgresql.conf for custom_variable_classes:
在 postgresql.conf 中为 custom_variable_classes 创建一个新设置：
custom_variable_classes = 'var'
Reload the config, you now have the variable "var" available in all your databases.
重新加载配置，您现在可以在所有数据库中使用变量“var”。
To create the variable p_country, just use SET:
要创建变量 p_country，只需使用 SET：
SET var.p_country = 'US';
SELECT current_setting('var.p_country') AS p_country;
It's not a beauty, but it works.
这不是一种美丽，但它有效。
回答by Wolph
Within a PL/pgSQL function you can declare variables like this:
在 PL/pgSQL 函数中，您可以像这样声明变量：
CREATE FUNCTION identifier (arguments) RETURNS type AS '
DECLARE
-- Declare an integer.
subject_id INTEGER;
-- Declare a variable length character.
book_title VARCHAR(10);
-- Declare a floating point number.
book_price FLOAT;
BEGIN
statements
END;
' LANGUAGE 'plpgsql';
