What is the difference between inner and outer join?.

Inner Join

Inner join is the most common type of Join which is used to combine the rows from two tables and create a result set containing only such records that are present in both the tables based on the joining condition

SELECT dept.name DEPARTMENT, emp.name EMPLOYEE 
FROM DEPT dept, EMPLOYEE emp
WHERE emp.dept_id = dept.id

Outer Join

Outer Join, on the other hand, will return matching rows from both tables as well as any unmatched rows from one or both the tables (based on whether it is single outer or full outer join respectively).

Notice in our record set that there is no employee in the department 5 (Logistics). Because of this if we perform inner join, then Department 5 does not appear in the above result. However in the below query we perform an outer join (dept left outer join emp), and we can see this department.

SELECT dept.name DEPARTMENT, emp.name EMPLOYEE 
FROM DEPT dept, EMPLOYEE emp
WHERE dept.id = emp.dept_id (+)

Pivot In SQL Query

We use pivot queries when we need to transform data from row-level to columnar data.

Pivot query help us to generate an interactive table that quickly combines and compares large amounts of data. We can rotate its rows and columns to see different summaries of the source data, and we can display the details for areas of interest at a glance. It also help us to generate Multidimensional reporting.

SELECT *
FROM (
    SELECT
        year(invoiceDate) as [year],left(datename(month,invoicedate),3)as [month],
        InvoiceAmount as Amount
    FROM Invoice
) as s
PIVOT
(
    SUM(Amount)
    FOR [month] IN (jan, feb, mar, apr,
    may, jun, jul, aug, sep, oct, nov, dec)
)AS pivot

SQL Wildcards

A wildcard character can be used to substitute for any other character(s) in a string.

Using the SQL % Wildcard

The following SQL statement selects all customers with a City starting with "ber":

SELECT * FROM table_Name
WHERE column_Name LIKE 'ber%';

Using the SQL _ Wildcard

The following SQL statement selects all customers with a City starting with any character, followed by "erlin":

SELECT * FROM table_Name
WHERE column_Name LIKE '_erlin';

Using the SQL [charlist] Wildcard

The following SQL statement selects all customers with a City starting with "b", "s", or "p":

SELECT * FROM table_Name
WHERE column_Name LIKE '[bsp]%';


The following SQL statement selects all customers with a City starting with "a", "b", or "c":

SELECT * FROM table_Name
WHERE column_Name LIKE '[a-c]%';

The following SQL statement selects all customers with a City NOT starting with "b", "s", or "p":

SELECT * FROM table_Name
WHERE column_Name LIKE '[!bsp]%';