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MySQL学习足迹记录08–创建计算字段–Concat(),AS
本文所用到的表格数据
mysql> SELECT * FROM vendors;+---------+----------------+-----------------+-------------+------------+----------+--------------------------------------------+| vend_id | vend_name | vend_address | vend_city | vend_state | vend_zip | vend_country |+---------+----------------+-----------------+-------------+------------+----------+---------------------------------------------+| 1001 | Anvils R Us | 123 Main Street | Southfield | MI | 48075 | USA || 1002 | LT Supplies | 500 Park Street | Anytown | OH | 44333 | USA || 1003 | ACME | 555 High Street | Los Angeles | CA | 90046 | USA || 1004 | Furball Inc. | 1000 5th Avenue | New York | NY | 11111 | USA || 1005 | Jet Set | 42 Galaxy Road | London | NULL | N16 6PS | England || 1006 | Jouets Et Ours | 1 Rue Amusement | Paris | NULL | 45678 | France |+---------+----------------+-----------------+-------------+------------+----------+-----------------------------------------------+6 rows in set (0.00 sec)
1.计算字段并不实际存在于数据库表中，计算字段是在运行时在SELECT语句内创建的。
2.拼接字段Concat()
*拼接：将值连结到一起构成单个值
拼接两个列
eg: mysql> SELECT Concat(vend_name,'(',vend_country,')') FROM vendors -> ORDER BY vend_name;+-------------------------------------------------------+| Concat(vend_name,'(',vend_country,')') |+--------------------------------------------------------+| ACME(USA) || Anvils R Us(USA) || Furball Inc.(USA) || Jet Set(England) || Jouets Et Ours(France) || LT Supplies(USA) |+---------------------------------------------------------+6 rows in set (0.00 sec)
3.删除右侧多余的空格RTrim()
删除左侧多余的空格LTrim()
删除两侧多余的空格Trim()
以RTrim()为例：
eg: mysql> SELECT Concat(RTrim(vend_name),'(',RTrim(vend_country),')') -> FROM vendors -> ORDER BY vend_name;+------------------------------------------------------+| Concat(RTrim(vend_name),'(',RTrim(vend_country),')') |+------------------------------------------------------+| ACME(USA) || An<div>本文来源gaodai.ma#com搞#代!码网_</div>vils R Us(USA) || Furball Inc.(USA) || Jet Set(England) || Jouets Et Ours(France) || LT Supplies(USA) |+------------------------------------------------------+6 rows in set (0.00 sec)
4.使用别名（alias),关键字AS
eg: mysql> SELECT Concat(Trim(vend_name),'(',Trim(vend_country),')') -> AS vend_title -> FROM vendors -> ORDER BY vend_name;+------------------------+| vend_title |+------------------------+| ACME(USA) || Anvils R Us(USA) || Furball Inc.(USA) || Jet Set(England) || Jouets Et Ours(France) || LT Supplies(USA) |+------------------------+6 rows in set (0.00 sec)
5.执行算术计算
先检索订单号20005中的所有物品
eg: mysql> SELECT prod_id,quantity,item_price -> FROM orderitems -> WHERE order_num = 20005;+---------+----------+------------+| prod_id | quantity | item_price |+---------+----------+------------+| ANV01 | 10 | 5.99 || ANV02 | 3 | 9.99 || TNT2 | 5 | 10.00 || FB | 1 | 10.00 |+---------+----------+------------+4 rows in set (0.00 sec)
再汇总物品的价格（单价*数量）
eg: mysql> SELECT prod_id,quantity,item_price, -> quantity*item_price AS expanded_price -> FROM orderitems -> WHERE order_num = 20005;+---------+----------+------------+----------------+| prod_id | quantity | item_price | expanded_price |+---------+----------+------------+----------------+| ANV01 | 10 | 5.99 | 59.90 || ANV02 | 3 | 9.99 | 29.97 || TNT2 | 5 | 10.00 | 50.00 || FB | 1 | 10.00 | 10.00 |+---------+----------+------------+----------------+4 rows in set (0.00 sec)
6.MySQL支持的基本算术操作符+,-,*,/
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转载请注明原文链接：MySQL学习足迹记录08–创建计算字段–Concat(),AS_MySQL
转载请注明原文链接：MySQL学习足迹记录08–创建计算字段–Concat(),AS_MySQL
