1 Create 唯一索引and普通索引
The table structure is as follows:
demand
To first_namecreate 唯一索引uniq_idx_firstname, to last_namecreate 普通索引idx_lastname.
SQL statement
create unique index uniq_idx_firstname on actor(first_name);
create index idx_lastname on actor(last_name);
2 转义符use
The table structure is as follows
demand
Connect all employees' last_namesums first_namewith '(single quotes).
SQL statement
select concat(last_name, '\'', first_name) as name from employees;
select concat(last_name, '''', first_name) as name from employees;
select concat(last_name, "'", first_name) as name from employees;
The above three statements can all be processed. The difference is that 'the processing method is different, and the commonly used one is to use backslash escape \.
operation result
3 subqueries `nested
The table structure is as follows
demand
Find belongs to Action分类all the movies of the corresponding title, description.
SQL statement
select title, description from film
where film_id in (select film_id from film_category where category_id =
(select category_id from category where name = "Action"));
Here's a query involves three tables title, descriptiononly the film表relevant, film_idthen with category表and film_category表related to the need 两重嵌套relationships.
operation result
4 Insert a record,忽略重复项
The table structure is as follows
demand
Insert a piece of data for the table actor, if the data already exists, please ignore
| actor_id | first_name | last_name | last_update |
|---|---|---|---|
| ‘3’ | ‘ED’ | ‘CHASE’ | ‘2006-02-15 12:34:33’ |
SQL statement
insert ignore into actor values ('3', 'ED', 'CHASE', '2006-02-15 12:34:33');
Use ignorekeywords to avoid the problem of primary key duplication
operation result
5 Insert the query result as a record into the table
The table structure is as follows
Table actor
Table actor_name
demand
The actor表all first_nameand last_nameimporting actor_name表.
SQL statement
insert into actor_name select first_name, last_name from actor;
operation result
