为MariaDB获取正确的SQL查询语法

Question

I am converting some SQL queries to run against MariaDB instead of via SQL Anywhere. One part of the query I need to update looks like this:

and datepart(mm,c.dob) = datepart(mm,today()) + 1

After consulting some MariaDB documentation, I think the second part may need to be this:

MONTH(NOW()) + 1

But, I'm not sure how to re-create the logic from the original line, since datepart is not used in MariaDB. When I try this, the query runs:

and MONTH(c.dob) = MONTH(NOW()) + 1

Does this look like the correct replacement syntax?

Answer 1

Hiding a column inside a function call prevents use of an index. Try to avoid such.

When doing date arithmetic, use syntax like this:

 date_value + INTERVAL 4 DAY

If using MONTH(NOW()) , what should you expect in December?

You can treat dates as strings in the format 2019-09-06 , so this is one way to get the start of the current month:

mysql> SELECT NOW(), CONCAT(LEFT(CURDATE(), 7), '-01');
+---------------------+-----------------------------------+
| NOW()               | CONCAT(LEFT(CURDATE(), 7), '-01') |
+---------------------+-----------------------------------+
| 2019-09-06 11:38:37 | 2019-09-01                        |
+---------------------+-----------------------------------+

Hence this will give you the start of next month, even in December:

CONCAT(LEFT(CURDATE(), 7), '-01') + INTERVAL 1 MONTH

It is usually preferable to compare dates than to pick apart a date -- I am thinking of the December issue. And leap-day.

WHERE my_date >= CONCAT(LEFT(CURDATE(), 7), '-01') + INTERVAL 1 MONTH

will check for my_date being next month (or later). This works whether my_date is DATE , DATETIME , or TIMESTAMP .

But, since dob is "date of birth", most of what I say is irrelevant, and you really need MONTH(dob)