Create a view and don't let the database update mysql? - mysql

Question

create table Branch
(
BranchNo char(4),
Street varchar(30),
City varchar(30),
PostCode varchar(10)
)
INSERT INTO BRANCH
VALUES ('B002', '55 cOVER', 'LONDON',NULL)
INSERT INTO BRANCH
VALUES ('B003', '163 Main Street', 'Glasgow',NULL)
INSERT INTO BRANCH
VALUES ('B004', '32 Manse Road', 'Bristol',NULL)
INSERT INTO BRANCH
VALUES ('B005', '22 Dear Road', 'LONDON',NULL)
INSERT INTO BRANCH
VALUES ('B007', '16 Argyll', 'Abend',NULL)
Create a view named ViewDeC that displays information of all branches. Must say
make sure it is not possible to update the data for the branch table (Branch) through this View
Create a view and don't let the database update mysql?
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Answer 1

If I am not mistaken, this is about how to create a readonly view. Though MySQL does not support creating a view with readonly attribute DIRECTLY, certain things can be done to make the view READONLY. One workaround is to make the view through joined tables.
create view ViewDeC as
select BranchNo,Street,City,PostCode
from Branch
join (select 1) t;
select * from ViewDec;
INSERT INTO ViewDec
VALUES ('B009', '99 Argyll', 'bender',NULL);
-- Error Code: 1471. The target table ViewDec of the INSERT is not insertable-into
Note, this is implemented at the cost of some performance, but not terribly unbearable. I have a table with 1.4 million rows. Here is the test with and without join using a table scan as the access method.
select * from proctable;
-- 1429158 rows in set (1.26 sec)
select * from proctable join (select 1) t;
-- 1429158 rows in set (1.40 sec)
However, for an index lookup access method, this is almost non-existent.
select * from proctable join (select 1) t where id between 100 and 500;
-- 401 rows in set (0.00 sec)
explain select * from proctable join (select 1) t where id between 100 and 500;
+----+-------------+------------+------------+--------+---------------+---------+---------+------+------+----------+----------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+------------+------------+--------+---------------+---------+---------+------+------+----------+----------------+
| 1 | PRIMARY | <derived2> | NULL | system | NULL | NULL | NULL | NULL | 1 | 100.00 | NULL |
| 1 | PRIMARY | proctable | NULL | range | PRIMARY | PRIMARY | 4 | NULL | 401 | 100.00 | Using where |
| 2 | DERIVED | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used |
+----+-------------+------------+------------+--------+---------------+---------+---------+------+------+----------+----------------+