mysql 中的字符串连接 CONCAT(str1,str2,...)
返回来自于参数连结的字符串。如果任何参数是NULL，返回NULL。可以有超过2个的参数。一个数字参数被变换为等价的字符串形式。
mysql> select CONCAT('My', 'S', 'QL');
-> 'MySQL'
mysql> select CONCAT('My', NULL, 'QL');
-> NULL
mysql> select CONCAT(14.3);
-> '14.3'
如：update test set ID=concat(ID,'ABC');
放在前面就连接到前面，放在后面就连接在后面。
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