同事問(wèn)MySQL數(shù)據(jù)類(lèi)型DECIMAL(N,M)中N和M分別表示什么含義，M不用說(shuō)，顯然是小數(shù)點(diǎn)后的小數(shù)位數(shù)，但這個(gè)N究竟是小數(shù)點(diǎn)之前的最大位數(shù)，還是加上小數(shù)部分后的最大位數(shù)？這個(gè)還真記不清了。于是乎，創(chuàng)建測(cè)試表驗(yàn)證了一番，結(jié)果如下：
測(cè)試表，seller_cost字段定義為decimal(14,2)
| CREATE TABLE `test_decimal` ( `id` int(11) NOT NULL, `seller_cost` decimal(14,2) DEFAULT NULL) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
起初，表中內(nèi)容為空
| mysql> select * from test_decimal;Empty set (0.00 sec) |
插入整數(shù)部分長(zhǎng)度為14的數(shù)字，報(bào)超出列范圍的錯(cuò)誤
| mysql> insert into test_decimal(id,seller_cost) values(1,12345678901234);ERROR 1264 (22003): Out of range value for column 'seller_cost' at row 1 |
插入整數(shù)部分長(zhǎng)度為12的數(shù)字，可以正確插入
| mysql> insert into test_decimal(id,seller_cost) values(1,123456789012);Query OK, 1 row affected (0.00 sec) |
查詢(xún)表，發(fā)現(xiàn)插入的整數(shù)值末尾被MySQL補(bǔ)了兩位小數(shù)“.00”
| mysql> select * from test_decimal;+----+-----------------+| id | seller_cost |+----+-----------------+| 1 | 123456789012.00 |+----+-----------------+1 row in set (0.00 sec) |
繼續(xù)插入整數(shù)部分12位，小數(shù)部分5位的數(shù)字，可以成功插入，但是有警告，警告表明小數(shù)部分發(fā)生了截?cái)啵唤厝〕闪藘晌恍?shù)
| mysql> insert into test_decimal(id,seller_cost) values(1,123456789012.12345);Query OK, 1 row affected, 1 warning (0.00 sec) mysql> show warnings;+-------+------+--------------------------------------------------+| Level | Code | Message |+-------+------+--------------------------------------------------+| Note | 1265 | Data truncated for column 'seller_cost' at row 1 |+-------+------+--------------------------------------------------+1 row in set (0.00 sec) mysql> select * from test_decimal;+----+-----------------+| id | seller_cost |+----+-----------------+| 1 | 123456789012.00 || 1 | 123456789012.12 |+----+-----------------+2 rows in set (0.00 sec) |
縮小整數(shù)部分的長(zhǎng)度為2，小數(shù)部分的長(zhǎng)度繼續(xù)保持為5，可以成功插入，但小數(shù)部分被截?cái)酁閮晌弧?/p>
| mysql> insert into test_decimal(id,seller_cost) values(1,12.12345);Query OK, 1 row affected, 1 warning (0.00 sec) mysql> show warnings;+-------+------+--------------------------------------------------+| Level | Code | Message |+-------+------+--------------------------------------------------+| Note | 1265 | Data truncated for column 'seller_cost' at row 1 |+-------+------+--------------------------------------------------+1 row in set (0.00 sec) mysql> select * from test_decimal;+----+-----------------+| id | seller_cost |+----+-----------------+| 1 | 123456789012.00 || 1 | 123456789012.12 || 1 | 12.12 |+----+-----------------+3 rows in set (0.00 sec) |
