MySQL中常见函数

mysql> SELECT NOW();
+---------------------+
| NOW()               |
+---------------------+
| 2019-10-19 10:55:28 |
+---------------------+
1 row in set (0.00 sec)

mysql> SELECT DATE_FORMAT(NOW(),‘%Y年-%m月-%d日 %H时:%i分:%s秒‘);
+----------------------------------------------------+
| DATE_FORMAT(NOW(),‘%Y年-%m月-%d日 %H时:%i分:%s秒‘) |
+----------------------------------------------------+
| 2019年-10月-19日 11时:03分:01秒                    |
+----------------------------------------------------+
1 row in set (0.00 sec)

mysql> SELECT DATE_ADD(NOW(),INTERVAL 1 DAY); 
+--------------------------------+
| DATE_ADD(NOW(),INTERVAL 1 DAY) |
+--------------------------------+
| 2019-10-20 11:07:47            |
+--------------------------------+
1 row in set (0.00 sec)

mysql> SELECT CONCAT(‘My‘,‘SQL‘);
+--------------------+
| CONCAT(‘My‘,‘SQL‘) |
+--------------------+
| MySQL              |
+--------------------+
1 row in set (0.00 sec)

mysql> SELECT FIELD(‘C‘,‘A‘,‘B‘,‘C‘,‘D‘);
+----------------------------+
| FIELD(‘C‘,‘A‘,‘B‘,‘C‘,‘D‘) |
+----------------------------+
|                          3 |
+----------------------------+
1 row in set (0.00 sec)

mysql> SELECT LOWER(‘ABCD‘);
+---------------+
| LOWER(‘ABCD‘) |
+---------------+
| abcd          |
+---------------+
1 row in set (0.00 sec)

mysql> SELECT REVERSE(‘ABCD‘);
+-----------------+
| REVERSE(‘ABCD‘) |
+-----------------+
| DCBA            |
+-----------------+
1 row in set (0.00 sec)

mysql> SELECT ABS(-10);
+----------+
| ABS(-10) |
+----------+
|       10 |
+----------+
1 row in set (0.00 sec)

mysql> SELECT ROUND(1.2345);
+---------------+
| ROUND(1.2345) |
+---------------+
|             1 |
+---------------+
1 row in set (0.00 sec)

mysql> SELECT RAND();
+--------------------+
| RAND()             |
+--------------------+
| 0.5442781900468079 |
+--------------------+
1 row in set (0.00 sec)

mysql> SELECT POW(4,2);  #4的2次方
+----------+
| POW(4,2) |
+----------+
|       16 |
+----------+
1 row in set (0.00 sec)

#返回 Products 表中Price 字段的平均值
mysql> SELECT AVG(price) AS AveragePrice FROM Products; 

#返回 Products 表中 products 字段总共有多少条记录：
mysql> SELECT COUNT(id) AS NumberOfProducts FROM Products;

#返回数据表 Products 中字段 Price 的最大值：
mysql> SELECT MAX(Price) AS LargestPrice FROM Products;

#返回数据表 Products 中字段 Price 的最小值：
mysql> SELECT MIN(Price) AS SmalltPrice FROM Products;

#计算 Products表中字段 Cost的总和：
mysql> SELECT SUM(Cost) AS TotalCost FROM Products;

mysql> SELECT GROUP_CONCAT(name) from crm_product;
+-----------------------+
| GROUP_CONCAT(name)    |
+-----------------------+
| 磷酸铁锂电池,叠片电池 |
+-----------------------+
1 row in set (0.00 sec)