What Is Drop Table If Exists?

What is drop table if exists?

The DROP TABLE statement deletes the specified table, and any data associated with it, from the database. The IF EXISTS clause allows the statement to succeed even if the specified tables does not exist. ... Attempting to drop the table before dropping the procedure will result in an error.

How can I see all tables in SQL?

Then issue one of the following SQL statement:

1. Show all tables owned by the current user: SELECT table_name FROM user_tables;
2. Show all tables in the current database: SELECT table_name FROM dba_tables;
3. Show all tables that are accessible by the current user:

How do I get a list of tables in MySQL?

In MySQL, there are two ways to find names of all tables, either by using "show" keyword or by query INFORMATION_SCHEMA. In the case of SQL Server or MSSQL, You can either use sys. tables or INFORMATION_SCHEMA to get all table names for a database.

How do I view a SQL query table?

This first query will return all of the tables in the database you are querying.

1. SELECT TABLE_NAME FROM INFORMATION_SCHEMA. TABLES.
2. SELECT TABLE_NAME, COLUMN_NAME FROM INFORMATION_SCHEMA. ...
3. SELECT COLUMN_NAME FROM INFORMATION_SCHEMA. ...
4. IF EXISTS( SELECT * FROM INFORMATION_SCHEMA. ...
5. IF EXISTS( SELECT * FROM INFORMATION_SCHEMA.

How do I view a SQL database?

In Object Explorer, connect to an instance of the SQL Server Database Engine, and then expand that instance. Expand Databases, right-click the database to view, and then click Properties. In the Database Properties dialog box, select a page to view the corresponding information.

How do I view an SQL database diagram?

To open a database diagram

1. In Object Explorer, expand the Database Diagrams folder.
2. Double-click the name of the database diagram you want to open. -or- Right-click the name of the database diagram you want to open, and then choose Design Database Diagram.

Can we insert and delete rows into a view?

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.

What is the difference between a table and a view?

A table consists of rows and columns to store and organized data in a structured format, while the view is a result set of SQL statements. A table is structured with columns and rows, while a view is a virtual table extracted from a database.

Which is faster table or view?

MS SQL Indexed views are faster than a normal view or query but indexed views can not be used in a mirrored database invironment (MS SQL). ... In this situation a temporary table using # or @ to hold your data to loop through is faster than a view or a query. So it all depends on the situation.

Is view better than table?

A view consists of rows and columns just like a table. The difference between a view and a table is that views are definitions built on top of other tables (or views), and do not hold data themselves. If data is changing in the underlying table, the same change is reflected in the view.

Can we drop a table that has dependent views on it?

DROP TABLE always removes any indexes, rules, triggers, and constraints that exist for the target table. ... (CASCADE will remove a dependent view entirely, but in the foreign-key case it will only remove the foreign-key constraint, not the other table entirely.)

Does drop table drop constraints?

When a table is dropped, rules or defaults on the table lose their binding, and any constraints or triggers associated with the table are automatically dropped. If you re-create a table, you must rebind the appropriate rules and defaults, re-create any triggers, and add all required constraints.

Does drop table drop index?

DROP TABLE removes tables from the database. ... DROP TABLE always removes any indexes, rules, triggers, and constraints that exist for the target table. However, to drop a table that is referenced by a view or a foreign-key constraint of another table, CASCADE must be specified.

What will happen when the following statement is executed drop table table name?

It completely removes the table structure and associated indexes, statistics, permissions, triggers and constraints. You might have SQL Views and Stored procedures referencing to the SQL table. SQL Server does not remove these stored procedures and views.

Does drop table need commit?

CREATE TABLE and DROP TABLE statements do not commit a transaction if the TEMPORARY keyword is used. ... SELECT causes an implicit commit before and after the statement is executed when you are creating nontemporary tables. (No commit occurs for CREATE TEMPORARY TABLE ... SELECT .)

How do I drop a table with constraints in SQL?

State' -- Drop the foreign key constraint by its name ALTER TABLE dbo....

1. Select the tables you want to DROP.
2. Select "Save to new query window".
3. Click on the Advanced button.
4. Set Script DROP and CREATE to Script DROP.
5. Set Script Foreign Keys to True.
6. Click OK.
7. Click Next -> Next -> Finish.
8. View the script and then Execute.

How do I drop a table in SQL query?

SQL DELETE Statement

1. DELETE FROM table_name WHERE condition;
2. Example. DELETE FROM Customers WHERE CustomerName='Alfreds Futterkiste';
3. DELETE FROM table_name;
4. Example. DELETE FROM Customers;

Which is better truncate or delete?

Truncate is faster compared to delete as it makes less use of the transaction log. Truncate is not possible when a table is referenced by a Foreign Key or tables are used in replication or with indexed views.

What is difference between truncate and delete?

Delete is a DML command whereas truncate is DDL command. ... Truncate can be used to delete the entire data of the table without maintaining the integrity of the table. On the other hand , delete statement can be used for deleting the specific data.

What is truncating a table?

TRUNCATE TABLE removes all rows from a table, but the table structure and its columns, constraints, indexes, and so on remain. To remove the table definition in addition to its data, use the DROP TABLE statement.

Is Drop table faster than truncate?

DROP is a DDL(Data Definition Language) command and is used to remove table definition and indexes, data, constraints, triggers etc for that table. Performance-wise the DROP command is quick to perform but slower than TRUNCATE because it gives rise to complications.

Why use truncate instead of delete?

TRUNCATE TABLE is faster and uses fewer system resources than DELETE , because DELETE scans the table to generate a count of rows that were affected then delete the rows one by one and records an entry in the database log for each deleted row, while TRUNCATE TABLE just delete all the rows without providing any ...

Does truncate table free space?

If you're using innodb_file_per_table=ON, or you're using MyISAM, TRUNCATE TABLE will delete the table files used by the table in question (and create new, empty ones). So, the space used will be released to the file system, and in Unix/Linux, “df” on the file system will show new space.

How do I free up space in SQL?

Freeing up space in local SQL Server Databases

1. Shrink the DB. There is often unused space within the allocated DB files (*. mdf).
2. Shrink the Log File. Same idea as above but with the log file (*. ldf).
3. Rebuild the indexes and then shrink the DB. If you have large tables the indexes are probably fragmented.

How do I free up space in MySQL?

Save your MySQL database from running out of disk space

1. Have a backup. ...
2. Stop the application. ...
3. Dump the unexported records to a file on another server: ...
4. Show last ID of events table as TRUNCATE will reset your sequence for IDs. ...
5. Delete all data from events table — this is the only way to reclaim disk space if you do not have enough space for doing OPTIMIZE TABLE.

How do you release free space in SQL?

To shrink a file in SQL Server, we always use DBCC SHRINKFILE() command. This DBCC SHRINKFILE() command will release the free space for the input parameter....For example,

1. Free space in Data file or Log file.
2. Heavy Transaction Log data file.
3. Increasing Log file Size and not shrinking due to heavy transaction stuck.