What are main queries of sql

Answer 1

do you mean main commands?
SELECT * FROM TableName WHERE Col1='OldValue'
UPDATE TableName SET Col1='Val1', Col2='Val2' WHERE Col1='OldValue'
INSERT INTO TableName (Col1,Col2) VALUES ('Val1','Val2')
DELETE FROM TableName WHERE Col1='OlDValue'

Answer 2

It depends. While taking the course databases I had to make a lot of sql queries. I think the most frequently used queries are just the simplest ones (if you are making a simple website, and there is no need for complex efficient queries). Some exemples:

SELECT *
FROM sometable
WHERE condition

SELECT someattribute
FROM table
WHERE attribute > ALL ( subquery )

SELECT someattribute
FROM table1, ( subquery) table2
WHERE condition

SELECT someattribute
FROM table1 JOIN table2 (some kind of join)

...

Answer 3

I agree with Enes.
The main SQL query would be as follows:

Select *
From <table name>
Where <condition>;