mysql数据库之函数、流程控制

函数

注意与存储过程的区别，mysql内置的函数只能在sql语句中使用！

参考博客：http://www.cnblogs.com/linhaifeng/articles/7495918.html#_label2

CREATE TABLE blog (
    id INT PRIMARY KEY auto_increment,
    NAME CHAR (32),
    sub_time datetime
);
​
INSERT INTO blog (NAME, sub_time)
VALUES
    ('第1篇','2015-03-01 11:31:21'),
    ('第2篇','2015-03-11 16:31:21'),
    ('第3篇','2016-07-01 10:21:31'),
    ('第4篇','2016-07-22 09:23:21'),
    ('第5篇','2016-07-23 10:11:11'),
    ('第6篇','2016-07-25 11:21:31'),
    ('第7篇','2017-03-01 15:33:21'),
    ('第8篇','2017-03-01 17:32:21'),
    ('第9篇','2017-03-01 18:31:21');
​
select date_format(sub_time,'%Y-%m'),count(id) from blog group by date_format(sub_time,'%Y-%m');

# 查询结果：

+-------------------------------+-----------+
| date_format(sub_time,"%Y-%m") | count(id) |
+-------------------------------+-----------+
| 2015-03 | 2 |
| 2016-07 | 4 |
| 2017-03 | 3 |
+-------------------------------+-----------+

流程控制

# if条件语句
delimiter //
CREATE PROCEDURE proc_if ()
BEGIN

    declare i int default 0;
    if i = 1 THEN
        SELECT 1;
    ELSEIF i = 2 THEN
        SELECT 2;
    ELSE
        SELECT 7;
    END IF;
​
END //
delimiter ;
# while循环
delimiter //
CREATE PROCEDURE proc_while ()
BEGIN
​
    DECLARE num INT ;
    SET num = 0 ;
    WHILE num < 10 DO
        SELECT
            num ;
        SET num = num + 1 ;
    END WHILE ;
​
END //
delimiter ;