| 類型 | 備注 |
|---|---|
| DATE | YYYY-MM-DD |
| DATETIME | YYYY-MM-DD HH:mm:ss |
| TIME | HH:mm:ss |
| DECIMAL | 通常用于帶小數位 |
| CHAR | 固定長度字符串 |
| NCHAR | 類型于CHAR一致 |
| SIGNED | 一個有符號的64整數位 |
| UNSIGNED | 一個無符號的64整數位 |
| BINARY | 二進制字符串 |
| JSON | MySQL 5.7.8 及更高版本 |
注意:
其中DATE支持的范圍是: 1000-01-01 至 9999-12-31，(實驗版本為:)
如果為: 999-01-01 結果則會0999-01-01。
如果為: 01-01-01則會為:2001-01-01。
mysql> select cast('999-11-11' as DATE);
+---------------------------+
| cast('999-11-11' as DATE) |
+---------------------------+
| 0999-11-11 |
+---------------------------+
1 row in set (0.00 sec)
mysql> select cast('01-11-11' as DATE);
+--------------------------+
| cast('01-11-11' as DATE) |
+--------------------------+
| 2001-11-11 |
+--------------------------+
1 row in set (0.00 sec)
mysql> select version(); +-----------+ | version() | +-----------+ | 5.7.20 | +-----------+ 1 row in set (0.00 sec)
2. CAST函數中expr的值可以轉換為type，其轉換的結果才正確，否則轉換后的結果默認值，如Null，0等。
例如：一個Char類型轉換為Demical類型，轉換的結果就為0。
mysql> SELECT CAST('ANDYQIAN' AS DECIMAL);
+-----------------------------+
| CAST('ANDYQIAN' AS DECIMAL) |
+-----------------------------+
| 0 |
+-----------------------------+
1 row in set, 1 warning (0.00 sec)
轉換案例
這里給出一些常用的類型轉換例子。
DATE 類型
mysql> select cast('2017-12-14' as DATE);
+----------------------------+
| cast('2017-12-14' as DATE) |
+----------------------------+
| 2017-12-14 |
+----------------------------+
1 row in set (0.00 sec)
TIME 類型
mysql> select cast('12:00:00' as TIME);
+--------------------------+
| cast('12:00:00' as TIME) |
+--------------------------+
| 12:00:00 |
+--------------------------+
1 row in set (0.00 sec)
DATETIM 類型
mysql> select cast('2017-12-14 00:11:11' as DATETIME);
+-----------------------------------------+
| cast('2017-12-14 00:11:11' as DATETIME) |
+-----------------------------------------+
| 2017-12-14 00:11:11 |
+-----------------------------------------+
1 row in set (0.00 sec)
SIGNED類型
mysql> select cast('-1024' as SIGNED);
+-------------------------+
| cast('-1024' as SIGNED) |
+-------------------------+
| -1024 |
+-------------------------+
1 row in set (0.00 sec)
UNSIGNED類型
mysql> select cast('-1024' as UNSIGNED);
+---------------------------+
| cast('-1024' as UNSIGNED) |
+---------------------------+
| 18446744073709550592 |
+---------------------------+
1 row in set, 1 warning (0.00 sec)
DECIMAL類型
mysql> select cast('18.11' as DECIMAL(18,2));
+--------------------------------+
| cast('18.11' as DECIMAL(18,2)) |
+--------------------------------+
| 18.11 |
+--------------------------------+
1 row in set (0.00 sec)
以上就是本次整理的全部內容，大家測試的時候可以輸入命令嘗試下，如果還有任何不明白的地方，大家可以在下方的留言區域討論。
