SQL

Question 1

What does CRUD stand for?

Answer 1

Create
Read
Update
Delete

Question 2

Example of Create in SQL?

Answer 2

INSERT INTO TableName (ColName1, ColName2)
VALUES (value1, value2)

Question 3

Example of Read in SQL?

Answer 3

SELECT column name
FROM table name
WHERE Condition is true
AND another Condition

Question 4

Example of Update in SQL?

Answer 4

UPDATE table name
SET column name = new value 1
WHERE column name = some value

Question 5

Example of Delete in SQL?

Answer 5

DELETE FROM table name
WHERE column name = some value

Question 6

Example of INNER JOIN in SQL?

Answer 6

SELECT TableName1.ColName1 TableName2.ColName2
FROM TableName1 JOIN TableName2 ON TableName1.PK = TableName2.FK

Question 7

What are the variations of the use of LIKE in SQL?

Answer 7

LIKE ‘Ber%’ (selects items with “ber” at the start).
LIKE ‘%co%’ (selects all customers with a city containing the pattern “co”)

Question 8

What does an NESTED SELECT look like in SQL?

Answer 8

SELECT ColumnName1
FROM TableName1
WHERE ColumnName1 =/IN (SELECT ColumnName2
FROM TableName2
WHERE ColumnName2 = someValue)

IN is used when more than one result will return.

Question 9

What are transactions?

Answer 9

BEGIN TRANSACTIONS;
They have to happen all at once as if there is a power cut, the data will be lost.

Question 10

What is the ACID principle?

Answer 10

Atomicity - all or nothing.
Consistent - all of the database rules must be followed.
Isolation - order of execution doesn’t matter.
Durability - once committed, the transaction must stay committed.

Question 11

What is record locking?

Answer 11

When a record is locked so it won’t get overwritten.