w将查询结果赋值给本地变量。
http://dev.mysql.com/doc/refman/5.7/en/stored-program-variables.html
Results from queries can be retrieved into local variables using SELECT ... INTO or by opening a cursor and using var_listFETCH ... INTO . See Section 14.2.9.1, “SELECT ... INTO Syntax”, and Section 14.6.6, “Cursors”.var_list
Results from queries can be retrieved into local variables
原文：http://www.cnblogs.com/yuanjiangw/p/6322674.html