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Database Articles
Page 254 of 547
How can we create a MySQL view with a subquery?
To illustrate the making of MySQL view with subquery we are using the following data from the table ‘Cars’ −mysql> select * from cars; +------+--------------+---------+ | ID | Name | Price | +------+--------------+---------+ | 1 | Nexa | 750000 | | 2 | Maruti Swift | 450000 | | 3 | BMW | 4450000 | | 4 | VOLVO | 2250000 | | 5 | Alto | 250000 | | 6 | Skoda ...
Read MoreWhere MySQL views can be inconsistent and how can we ensure their consistency?
In case of updateable views, it is quite possible that we update the data that is not visible through the view because we create a view to revealing only the partial data of a table. Such kind of updates makes the view inconsistent. We can ensure the consistency of views by using WITH CHECK OPTION while creating or modifying the views. Although WITH CHECK OPTION clause is an optional part of CREATE VIEW statement but it is very useful to make views consistent.Basically, the WITH CHECK OPTION clause prevents us from updating or inserting the rows which are not visible ...
Read MoreHow can I create a MySQL view that takes the values from a table based on some condition(s)?
If we want to create a view that takes the values from a table based on some particular condition(s) then we have to use WHERE clause while creating the view. The values depending upon the WHERE clause will be stored in view. The syntax of creating a MySQL view with WHERE clause can be as follows −SyntaxCreate View view_name AS Select_statements FROM table WHERE condition(s);ExampleTo illustrate the above concept, we are using the following data from table ‘Student_info’ −mysql> Select * from student_info; +------+---------+------------+------------+ | id | Name | Address | Subject ...
Read MoreHow can we see the metadata of a view(s) stored in a particular MySQL database?
The INFORMATION_SCHEMA database has a VIEWS table that contains view metadata i.e. data about views. To illustrate it we are taking the example of a view named ‘Info’.ExampleThe following query will show the metadata of a view named ‘Info’ −mysql> SELECT * from INFORMATION_SCHEMA.VIEWS WHERE TABLE_NAME = 'Info' AND TABLE_SCHEMA = 'query'\G *************************** 1. row *************************** TABLE_CATALOG: def TABLE_SCHEMA: query TABLE_NAME: info VIEW_DEFINITION:select`query`.`student_info`.`id`AS`ID`, `query`.`student_info`.`Name` AS `NAME`, `query`.`student_info`.`Subject` AS `SUBJECT`, `query`.` student_info`.`Address` AS `ADDRESS` from `query`.`student_info` CHECK_OPTION: NONE IS_UPDATABLE: YES ...
Read MoreHow can we get the structure of a MySQL view as we can get the structure of a MySQL table?
As we know that views are a type of virtual tables and are a composition of tables too hence we can use the same query to get the structure of a view which we use to get the structure of a table. In other words, we can use DESCRIBE statement to get the structure of a MySQL view. Its syntax would be as follows −SyntaxDESCRIBE view_name;Here, view_name is the name of the view of which we want to get the structure.ExampleSuppose we want to get the structure of a view named ‘Info’ then it can be done with the help, of the following query ...
Read MoreHow can we list all the columns of a MySQL view as we can list the columns of a MySQL table?
As we know that views are a type of virtual tables and are the composition of tables too hence we can use the same query to list all the columns of a MySQL view as we can list the columns of a MySQL table. In other words, we can use SHOW FULL COLUMNS statement to get the structure of a MySQL view. Its syntax would be as follows −SyntaxSHOW FULL COLUMNS FROM View_name;Here view_name is the name of the view from which we want to get the list of columns.ExampleSuppose if we want to get a list of columns of ...
Read MoreHow can we update any value in MySQL view as we can update the values in MySQL table?
As we know that with the help of UPDATE statement we can update the values in MySQL table and in the similar way we can update the values in MySQL views. The syntax of UPDATE statement would be the same except at the place of table name we have to provide the name of the view. We are taking the data as follows from a view named ‘Info’ to illustrate the above concept −mysql> Select * from Info; +------+---------+------------+ | Id | Name | Subject | +------+---------+------------+ | 101 | YashPal ...
Read MoreAfter updating any value in a particular view, will MySQL updates the same in the base table and its associated views (if any)?
Yes, MySQL will update the value, if it is updated in a view, in the base table as well as in its associated views. To illustrate it we are taking the example of table Student_info having the following data −mysql> Select * from student_info; +------+---------+------------+------------+ | id | Name | Address | Subject | +------+---------+------------+------------+ | 101 | YashPal | Amritsar | History | | 105 | Gaurav | Chandigarh | Literature | | 125 | Raman | Shimla | Computers | | NULL | Ram | Jhansi ...
Read MoreHow can we get the total number of rows affected by MySQL query?
MySQL ROW_COUNT() can be used to get the total number of rows affected by MySQL query. To illustrate it we are creating a procedure with the help of which we can insert records in a table and it will show us how many rows have been affected.Examplemysql> Delimiter // mysql> CREATE PROCEDURE `query`.`row_cnt` (IN command VarChar(60000)) -> BEGIN -> SET @query = command; -> PREPARE stmt FROM @query; -> EXECUTE stmt; -> SELECT ROW_COUNT() AS 'Affected rows'; -> END // Query OK, 0 rows ...
Read MoreHow can we use MySQL REPLACE statement to prevent of insertion of duplicate data?
We can use the REPLACE statement while inserting the data to prevent the insertion of duplicate data. If we will use the REPLACE command rather than the INSERT command then if the record is new, it is inserted just as with INSERT else if it is a duplicate, the new record replaces the old one.SyntaxREPLACE INTO table_name(…)Here, table_name is the name of the table in which we want to insert the values.ExampleIn this example we will insert the data with the help of REPLACE statement as follows −mysql> REPLACE INTO person_tbl (last_name, first_name) -> VALUES( 'Ajay', 'Kumar'); Query OK, ...
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