如何在MySQL中将“ MONTHNAME（）”函数设置为列默认值？

Question

Actually I need current month name as lowercase string as default value in one of the table column; DB table may look like Like:

name : john
joined : january

When I try to use mysql function LOWER( MONTHNAME( NOW() ) ) as defailt value this gives me error. Btw I'm not interested in creating triggers.

any magic queries to do that?

Answer 1

From the MySQL documentation :

With one exception, enclose expression default values within parentheses to distinguish them from literal constant default values.

So, the following should work:

CREATE TABLE yourTable (
    month_name VARCHAR(12) DEFAULT (LOWER(MONTHNAME(NOW())))
    ...
)

As @Madhur has pointed out, using an expression as a default will only work from MySQL 8 onwards.

Answer 2

If you use MySQL 8.0 or later, then the answers provided by @TimBiegeleisen and @fa06 should solve the problem. In otherwise

... the default value specified in a DEFAULT clause must be a literal constant; it cannot be a function or an expression.

See details in documentation .

So, for previous versions you need to find another way. For example, you could define a trigger that sets default value for the column if the value is not specified:

CREATE TABLE MyTable (
  id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
  name VARCHAR(50),
  joined  VARCHAR(12)
);

CREATE TRIGGER defaultMonth
BEFORE INSERT ON MyTable
FOR EACH ROW 
SET NEW.joined = IFNULL(NEW.joined, LOWER(MONTHNAME(NOW())));

See also live example for the proposed solution.

Answer 3

You can try below

CREATE TABLE orderdata (

    order_date DATE
  , order_month VARCHAR(50) AS (lower(MONTHNAME(order_date))) 

);