mysql 資料字元串連函數CONCAT

CONCAT()是字串串連函數
REPLACE()是字串替換函數

CONCAT(參數1,參數2,...)

CONCAT(字串,from_str,to_str)
返回字串str，其字串from_str的所有出現 由 字串to_str代替.

個衍生函數是concat_ws(separator,string1,string2,...)

它與concat的區別在於,串連後,在串連處有一個分隔字元separator.如:

update users set homedir=concat_ws(´/´,´/data/disk1´,´part1´,´user1´) where userid=´user1´;

其結果是user1的homedir=´/data/disk1/part1/user1´

CONCAT(str1,str2,...)

Returns the string that results from concatenating the arguments. Returns NULL if any argument is NULL. May have one or more arguments. If all arguments are non-binary strings, the result is a non-binary string. If the arguments include any binary strings, the result is a binary string. A numeric argument is converted to its equivalent binary string form; if you want to avoid that you can use explicit type cast, like in this example: select CONCAT(CAST(int_col AS CHAR), char_col)

mysql> select CONCAT('My', 'S', 'QL');
-> 'MySQL'
mysql> select CONCAT('My', NULL, 'QL');
-> NULL
mysql> select CONCAT(14.3);
-> '14.3'