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nd individual wrapping.' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(102, 'OL1', '2005-08-18', 'Can shipped full, refills not available. Need to order new can if refill needed.' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(103, 'SAFE', '2005-08-18', 'Safe is combination locked, combination not provided with safe. This is rarely a problem as safes are typically blown up or dropped by customers.' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(104, 'FC', '2005-08-19', 'Quantity varies, sold by the sack load. All guaranteed to be bright and orange, and suitable for use as rabbit bait.' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(105, 'TNT2', '2005-08-20', 'Included fuses are short and have been known to detonate too quickly for some customers. Longer fuses are available (item FU1) and should be recommended.' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(106, 'TNT2', '2005-08-22', 'Matches not included, recommend purchase of matches or detonator (item DTNTR).' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(107, 'SAFE', '2005-08-23', 'Please note that no returns will be accepted if safe opened using explosives.' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(108, 'ANV01', '2005-08-25', 'Multiple customer returns, anvils failing to drop fast enough or falling backwards on purchaser. Recommend that customer considers using heavier anvils.' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(109, 'ANV03', '2005-09-01', 'Item is extremely heavy. Designed for dropping, not recommended for use with slings, ropes, pulleys, or tightropes.' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(110, 'FC', '2005-09-01', 'Customer complaint: rabbit has been able to detect trap, food apparently less effective now.' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(111, 'SLING', '2005-09-02', 'Shipped unassembled, requires common tools (including oversized hammer).' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(112, 'SAFE', '2005-09-02', 'Customer complaint: Circular hole in safe floor can apparently be easily cut with handsaw.' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(113, 'ANV01', '2005-09-05', 'Customer complaint: Not heavy enough to generate flying stars around head of victim. If being purchased for dropping, recommend ANV02 or ANV03 instead.' ); INSERT INTO productnotes(note_id, prod_id, note_date, note_text) VALUES(114, 'SAFE', '2005-09-07', 'Call from individual trapped in safe plummeting to the ground, suggests an escape hatch be added. Comment forwarded to vendor.' );
mysql> SHOW TABLES;
+———————–+
| Tables_in_crashcourse |
+———————–+
| customers |
| orderitems |
| orders |
| productnotes |
| products |
| vendors |
+———————–+
6 rows in set (0.00 sec)
mysql> SHOW COLUMNS FROM products;
![这里写图片描述](https://www.cppentry.com/upload_files/article/57/1_c6cjl__.png "\")
mysql> SELECT prod_id, vend_id, prod_name, prod_price FROM products;
![这里写图片描述](https://www.cppentry.com/upload_files/article/57/1_w5fwi__.png "\")
二、MySQL创建和操作表
创建和操作表的代码参考上面 create.sql
2.1 NULL
NULL 代表允许在插入行时不给出该列的值，NOT NULL 代表该列不接受没有值的行。
2.2 主键
主键可是是一列，也可以是多列，如果使用多列，则这些列的组合必须唯一，比如：
PRIMARYKEY (order_num, order_item)
2.3 关于 AUTO_INCREMENT
如果某列被指定为 AUTO_INCREMENT，每插入一行该列自动增长，也可以简单的在 INSERT 语句中指定一个值，只要它是唯一的即可，该值将被用来替代自动生成的值，后续的增量将开
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