How to delete data from a table using the DELETE
statement in SQL
Answer: Use the DELETE
statement to remove data from a table
For example:
Explain the concept of an Index
and the benefits of using Indexes in SQL
Answer: An Index
is a data structure that improves the speed of data retrieval in a database. It is created on one or more columns of a table and helps to reduce the time required for searching and sorting data. The benefits of using Indexes include improved query performance and faster data retrieval.
How to use the CREATE TABLE
statement to create a new table in SQL
Answer: Use the CREATE TABLE
statement to create a new table in the database.
For example:
How to use the ALTER TABLE
statement to add a new column to a table in SQL.
Answer: Use the ALTER TABLE
statement to add a new column to an existing table.
For example:
How to use the DROP TABLE
statement to delete a table in SQL
Answer: Use the DROP TABLE
statement to remove a table from the database.
For example:
Explain how to use the UNION
and UNION ALL
statements in SQL
Answer:
UNION
: Combines the results of two or moreSELECT
queries into a single result set and removes duplicates.UNION ALL:
Similar toUNION
, but retains duplicate rows.
How to use the LIKE
statement and special characters in search conditions in SQL
Answer: Use the LIKE statement to perform pattern matching for text search. There are two special characters commonly used with LIKE
:
- %: Represents any string of characters, including zero or more characters.
- _: Represents a single character.
Explain the different data retrieval queries: SELECT, SELECT DISTINCT, SELECT TOP
in SQL
Answer:
SELECT
: Retrieves data from one or more tables.SELECT DISTINCT
: Retrieves unique data from a column, removing duplicate values.SELECT TOP
: Retrieves a specified number of rows from the query result.
How to use the GROUP BY, HAVING, ORDER BY
statements together in SQL
Answer: By combining the GROUP BY, HAVING, ORDER BY
statements, we can group data, filter groups, and sort the result.
For example:
Explain the concept of a transaction
and how to use the BEGIN TRANSACTION, COMMIT, ROLLBACK
statements in SQL.
Answer: A transaction is a sequence of one or more database operations treated as a single unit. If any of the operations within the transaction fail, the entire transaction is rolled back and all changes are undone.
BEGIN TRANSACTION
: Starts a new transaction.COMMIT
: Saves and confirms the changes made in the transaction to the database.ROLLBACK
: Cancels the transaction and undoes any changes made in the transaction