MySQL SQL 问题

SELECT * FROM user WHERE user_id = *

user_id = 全部 怎么写

补充代码，如果为空， urlname = ???; name = ???; email = ???; 这3个怎么写

javapublic User get(String urlname, String name, String email) {
    try {
        if (urlname == null) {
            urlname = ???;
        }
        if (name == null) {
            name = ???;
        }
        if (email == null) {
            email = ???;
        }
        String sql = "SELECT * FROM tz_user WHERE deleting = 0 AND urlname = ? AND name = ? AND email = ?";
        RowMapper<User> rowMapper = new BeanPropertyRowMapper<User>(User.class);
        User user = jdbcTemplate.queryForObject(sql, rowMapper, urlname, name, email);
        return user;
    } catch (Exception e) {
        return null;
    }
}

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SELECT * FROM user

SELECT * FROM user where uid like %

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判断 urlname, name, email为空的时候最好用 StringUtils.isNotBlank 来判断字符串是否不为空且长度不为0且不由空白符(whitespace)构成.

try {
StringBuffer sql = "SELECT * FROM tz_user WHERE deleting = 0 ";
if (StringUtils.isNotBlank(urlname)) {
sql.append( "and urlname = "+ ???);
}
if (StringUtils.isNotBlank(name)) {
sql.append( "and name= "+ ???);
}
if (StringUtils.isNotBlank(email)) {
sql.append( "and email= "+ ???);
}
RowMapper rowMapper = new BeanPropertyRowMapper(User.class);
User user = jdbcTemplate.queryForObject(sql.toString(), rowMapper, urlname, name, email);
return user;
} catch (Exception e) {
return null;
}