正则表达式将字符串中的所有连续空格替换成一个空格

Replace two or more spaces with a single space.

JAVA :
String oldStr = "AAA BBB";
String newStr =oldStr.replaceAll(" {2,}"," ");

JS :
var oldStr = "AAA BBB";
var newStr =oldStr.replace(//s{2,}/g," ");

SQL :
If there two records in table A,the s of A2 is "aa bb" and "aaa bbb".
We can use the like :
UPDATE A SET A2=REGEXP_REPLACE(A2,'( ){2,}',' '),and then the new s of A2 is "aa bb" and "aaa bbb".