Question: What Is The Use Of Drop Command?

What is Delete command?

DELETE command is used to delete data from a table.

Following is its general syntax, DELETE FROM table_name; Let’s take a sample table student: s_id..

What is the difference between where and having clause?

WHERE Clause is used to filter the records from the table based on the specified condition. … HAVING Clause is used to filter record from the groups based on the specified condition.

What does the drop command do?

The drop table command is used to delete a table and all rows in the table. … Deleting all of the records in the table leaves the table including column and constraint information. Dropping the table removes the table definition as well as all of its rows.

Why drop table if exists?

The DROP TABLE SQL statement enables you to delete a table from the database. If the table did not exist then attempting to DROP it would cause an error to occur. The DROP TABLE IF EXISTS SQL statement enables a check to see that the table exists prior to attempting the dropping (deletion) of the table.

Which is faster truncate or drop?

TRUNCATE is a DDL(Data Definition Language) command. It is used to delete all the tuples from the table. Like the DROP command, the TRUNCATE command also does not contain a WHERE clause. The TRUNCATE command is faster than both the DROP and the DELETE command.

What are 2 differences between delete and truncate?

Delete and truncate both commands can be used to delete data of the table. 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.

How do I drop all tables?

How to drop all tables in MySQL?SET FOREIGN_KEY_CHECKS = 0; … SELECT table_name FROM information_schema.tables WHERE table_schema = db_name; … DROP TABLE IF EXISTS table1; DROP TABLE IF EXISTS table2; DROP TABLE IF EXISTS table3; … SET FOREIGN_KEY_CHECKS = 1; … echo “SET FOREIGN_KEY_CHECKS = 0;” > ./temp.sql.More items…•

What is modify command?

The MODIFY command can change certain user, application, and global variables. For example, you can put limits on the following parameters: The number of users logged on.

What is difference between drop and delete?

DELETE is a Data Manipulation Language command, DML command and is used to remove tuples/records from a relation/table. Whereas DROP is a Data Definition Language, DDL command and is used to remove named elements of schema like relations/table, constraints or entire schema. … DELETE is DML. DROP is DDL.

What is the use of drop command and what are the differences between drop truncate and delete commands?

DROP TABLE vs. DELETE TABLE vs. TRUNCATE TABLE in SQLDELETEDROPWorks in WHEREYesNoRemoves …One, some, or all rows in a table.Entire table structure: data, privileges, indexes, constraints, triggers.Resets ID auto-incrementNoDoesn’t applyRollbackYesMySQL: No Oracle: Yes PostgreSQL: Yes SQL Server : Yes7 more rows•Jun 24, 2020

Does truncate free space?

A TRUNCATE statement does not affect any structures associated with the table being truncated (constraints and triggers) or authorizations. A TRUNCATE statement also specifies whether space currently allocated for the table is returned to the containing tablespace after truncation.

How do you check if a table exists in SQL?

To check if a table exists in SQL Server, you can use the INFORMATION_SCHEMA. TABLES table. You can use this table with an IF THEN clause do determine how your query responds whether or not a table exists.

How do you drop a table if it exists in SQL?

SQL Server DROP TABLEFirst, specify the name of the table to be removed.Second, specify the name of the database in which the table was created and the name of the schema to which the table belongs. The database name is optional. … Third, use IF EXISTS clause to remove the table only if it exists.

Is update a DDL command?

DDL is Data Manipulation Language and is used to manipulate data. Examples of DML are insert, update and delete statements. … DDL statements are used to create database, schema, constraints, users, tables etc. DML statement is used to insert, update or delete the records.

Which is better truncate or delete?

Truncate reseeds identity values, whereas delete doesn’t. Truncate removes all records and doesn’t fire triggers. Truncate is faster compared to delete as it makes less use of the transaction log.

Can we rollback truncate?

You cannot ROLLBACK TRUNCATE Simply, you cannot rollback a transaction if it is already committed but you can do something else to get the data back (or at least some parts of it). When you execute the TRUNCATE statement, your data is still in the MDF file.

What are the DML commands?

Some commands of DML are:SELECT – retrieve data from the a database.INSERT – insert data into a table.UPDATE – updates existing data within a table.DELETE – deletes all records from a table, the space for the records remain.MERGE – UPSERT operation (insert or update)CALL – call a PL/SQL or Java subprogram.More items…•

Which one sorts rows in SQL?

The SQL ORDER BY Keyword The ORDER BY keyword is used to sort the result-set in ascending or descending order. The ORDER BY keyword sorts the records in ascending order by default. To sort the records in descending order, use the DESC keyword.

What is the use of alter command?

SQL ALTER TABLE Statement. The ALTER TABLE statement is used to add, delete, or modify columns in an existing table. The ALTER TABLE statement is also used to add and drop various constraints on an existing table.

Is Grant DDL or DML?

Data definition language (DDL) statements let you to perform these tasks: Create, alter, and drop schema objects. Grant and revoke privileges and roles. Analyze information on a table, index, or cluster.

How do you drop a database?

The DROP DATABASE statement allows you to delete one or more databases with the following syntax: DROP DATABASE [ IF EXISTS ] database_name [,database_name2,…]; In this syntax, you specify the name of the database that you want to drop after the DROP DATABASE keywords.