How do I drop a view?

How do I drop a view?

The syntax for the SQL DROP VIEW Statement is: DROP VIEW view_name; view_name. The name of the view that you wish to drop.

What will happen if a view is dropped?

If a VIEW, by definition of a view, is a subset of that which is in the database (whether on one or more tables), then if you drop even one of those tables then then VIEW becomes invalid. Therefore according to database logic such a View cannot exist. (All the data in that table is 'destroyed' on dropping).

How do you define a drop view in SQL?

Dropping a View in an database is not as scary as dropping a table or rows of data. Since a view is a virtual table, it is relatively easy to drop the view and begin again. The syntax is DROP VIEW followed by the table name: use the IF EXISTS command to make sure the system checks for the existence of the table.

How are views created and dropped?

We can create a view by selecting fields from one or more tables present in the database. A View can either have all the rows of a table or specific rows based on certain condition. In this article we will learn about creating , deleting and updating Views. We can create View using CREATE VIEW statement.

Can we insert and delete rows into a view?

You can insert, update, and delete rows in a view, subject to the following limitations: If the view contains joins between multiple tables, you can only insert and update one table in the view, and you can't delete rows. You can't directly modify data in views based on union queries.

Is view faster than query MySQL?

3 Answers. No, a view is simply a stored text query. You can apply WHERE and ORDER against it, the execution plan will be calculated with those clauses taken into consideration.

Is a view faster than a query?

Views make queries faster to write, but they don't improve the underlying query performance. ... In short, if an indexed view can satisfy a query, then under certain circumstances, this can drastically reduce the amount of work that SQL Server needs to do to return the required data, and so improve query performance.

Which is faster stored procedure or view?

A view is essentially a saved SQL statement. Therefore, I would say that in general, a stored procedure will be likely to be faster than a view IF the SQL statement for each is the same, and IF the SQL statement can benefit from optimizations. Otherwise, in general, they would be similar in performance.

Why is MySQL running slow?

If a query is too complicated and the code is not optimized, it will use more CPU. If the queries are causing the database to hit the upper limits of its allotted CPU, the database will become slow.

How can I see which MySQL queries are running slow?

To enable the slow query log, type the following command at the mysql> prompt: SET GLOBAL slow_query_log = 'ON'; There are additional options that you can set for the slow query log: By default, when the slow query log is enabled, it logs any query that takes longer than 10 seconds to run.

What is slow query in MySQL?

The MySQL slow query log is where the MySQL database server registers all queries that exceed a given threshold of execution time. This can often be a good starting place to see which queries are slowest and how often they are slow. MySQL on your server is configured to log all queries taking longer than 0.

Does limit speed up query?

The answer, in short, is yes. If you limit your result to 1, then even if you are "expecting" one result, the query will be faster because your database wont look through all your records. It will simply stop once it finds a record that matches your query.

Can I use offset without limit?

theory (iovation) asked a question. How do I use OFFSET without LIMIT? The LIMIT / FETCH docs claim PostgreSQL support for LIMIT and OFFSET, but Postgres does not require LIMIT to use OFFSET, while Snowflake does.

What is query limit?

The limit keyword is used to limit the number of rows returned in a query result. ... "LIMIT N" is the keyword and N is any number starting from 0, putting 0 as the limit does not return any records in the query.

What is top in MySQL?

The SELECT TOP clause is used to specify the number of records to return. The SELECT TOP clause is useful on large tables with thousands of records. ... Note: Not all database systems support the SELECT TOP clause. MySQL supports the LIMIT clause to select a limited number of records, while Oracle uses ROWNUM.

How do I select top 5 rows in SQL?

SQL SELECT TOP Clause

  1. SQL Server / MS Access Syntax. SELECT TOP number|percent column_name(s) FROM table_name;
  2. MySQL Syntax. SELECT column_name(s) FROM table_name. LIMIT number;
  3. Example. SELECT * FROM Persons. LIMIT 5;
  4. Oracle Syntax. SELECT column_name(s) FROM table_name. WHERE ROWNUM 25000; If there were two salaries of $30,000/year, only one of these values would be used in the AVG function.

    How do I find the second largest number in SQL?

    SELECT MAX (column_name) FROM table_name WHERE column_name NOT IN (SELECT Max (column_name) FROM table_name); First we selected the max from that column in the table then we searched for the max value again in that column with excluding the max value which has already been found, so it results in the 2nd maximum value.

    How do I find the second largest number in mysql?

    To get the *N*th highest value, better to use this solution: SELECT * FROM `employees` WHERE salary = (SELECT DISTINCT(salary) FROM `employees` ORDER BY salary DESC LIMIT {N-1},1); or you can try with: SELECT * FROM `employees` e1 WHERE (N-1) = (SELECT COUNT(DISTINCT(salary)) FROM `employees` e2 WHERE e1.

    What is Rownum in SQL?

    For each row returned by a query, the ROWNUM pseudocolumn returns a number indicating the order in which Oracle selects the row from a table or set of joined rows. The first row selected has a ROWNUM of 1, the second has 2, and so on. ... The results can vary depending on the way the rows are accessed.

    What is trigger in SQL?

    A trigger is a special type of stored procedure that automatically runs when an event occurs in the database server. DML triggers run when a user tries to modify data through a data manipulation language (DML) event. ... SQL Server lets you create multiple triggers for any specific statement.

    How do you trigger in SQL?

    Creating Triggers

    1. CREATE [OR REPLACE] TRIGGER trigger_name − Creates or replaces an existing trigger with the trigger_name.
    2. {BEFORE | AFTER | INSTEAD OF} − This specifies when the trigger will be executed. ...
    3. {INSERT [OR] | UPDATE [OR] | DELETE} − This specifies the DML operation.

    How do you run a trigger in SQL?

    This article explains the execution order of triggers In SQL. Triggers are stored programs that are automatically executed or fired when a specified event occurs. It is a database object that is bound to a table and is executed automatically....Execution Order of Triggers In SQL.
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    What does (+) mean in SQL JOIN?

    outer join