MySql- VII single-table queries

1, MySQL can use +, -, *, /.

    1 "is not provided in the MySQL string concatenation operator, you may be used concat (a_str, 'xxx') are connected.

    2 "with a null in an arithmetic expression, it will cause the entire return arithmetic expression is null, the result is obtained in the null string connection.

2, some of the syntax

    1 "can play an alias for a field, then use a space or as a field with an alias. If the alias has spaces or case sensitive, can be achieved by double quotes as an alias.

select e_id+5 "My id"
from emp;