レコードの更新､削除

update users set score = 5.9;

update users set score = 5.9 where id = 1;

update users set name = 'sasaki', score = 2.9 where name = 'tanaka';

delete from users;

delete from users where score < 5.0;

数値の演算

+ - * / %

id が偶数の人のスコアを 1.2倍する。
update users set score = score * 1.2 where id % 2 = 0;

select round(5.355);　　-> 5

select round(5.355, 1); 　-> 5.4

select floor(5.833); 　-> 5

select ceil(5.238); 　-> 6

select rand();
＊rand() を使うと 0 以上 1 未満のランダムな数値を返す。

select * from users order by rand() limit 1;

select length('Hello'); 　--> 5

select substr('Hello', 2);　-->ello
select substr('Hello', 2, 3);　-->ell

select upper('Hello');　--> HELLO

select lower('HELLO');　-->hello

select concat('hello', 'world');　--> helloworld

elect length(name), name from users order by length(name);

select length(name) as len, name from users order by len;