Which of the following statements are correct?

Explanation

DROP TABLE statement is used to drop an existing table in a database.
DELETE statement is used to delete existing records in a table.
There is no REMOVE statement in SQL.
ALTER TABLE statement is used to modify the table structure - add, delete, or modify columns in an existing table, add and drop various constraints on it.

Theory

SQL DROP INDEX, DROP TABLE, and DROP DATABASE
Indexes, tables, and databases can easily be deleted/removed with the DROP statement.
Read more: SQL DROP
The DROP INDEX Statement
The DROP INDEX statement is used to delete an index in a table.
DROP INDEX Syntax for MS Access:
```
DROP INDEX index_name ON table_name
```
DROP INDEX Syntax for MS SQL Server:
```
DROP INDEX table_name.index_name
```
DROP INDEX Syntax for DB2/Oracle:
```
DROP INDEX index_name
```
DROP INDEX Syntax for MySQL:
```
ALTER TABLE table_name DROP INDEX index_name
```
Read more: SQL DROP
The DROP TABLE Statement
The DROP TABLE statement is used to delete a table.
```
DROP TABLE table_name
```
Read more: SQL DROP
The DROP DATABASE Statement
The DROP DATABASE statement is used to delete a database.
```
DROP DATABASE database_name
```
Read more: SQL DROP
The TRUNCATE TABLE Statement
What if we only want to delete the data inside the table, and not the table itself?
Then, use the TRUNCATE TABLE statement:
```
TRUNCATE TABLE table_name
```
Read more: SQL DROP
SQL DELETE Statement
The DELETE statement is used to delete records(rows) in a table.
Syntax
```
DELETE FROM table_name
WHERE some_column=some_value;
```
Note
Notice the WHERE clause in the SQL DELETE statement! The WHERE clause specifies which record or records that should be deleted. If you omit the WHERE clause, all records will be deleted!
Read more.