SQL for QA - Full Course

Basic SQL commands for QA

On this page, I will help you collect the basic SQL command that you will use to test Database of your product.

Please follow this video to setup a local database at your computer first.

We will use it to practice Basic SQL commands.

+ Select command

Select command is the command to query data of a table. Here is the syntax of basic Select command:

SELEECT * FROM schema_name.table_name WHERE <condition>

Example:

• We query data of all column of actor table, we will run this command:

SELECT * FROM public.actor;

• Select with condition

SELECT * FROM public.actor where actor_id = 10;

• Limit

If the result of a query has many record, we can use Limit function to limit the number of record return in a query command:

SELECT * FROM public.actor limit 5;

+ Order by:

In some cases query result returns rows in an unspecified order. , To sort the rows of the result set, you use the ORDER BY clause in the SELECT statement.

The ORDER BY clause allows you to sort rows returned by a SELECT clause in ascending (ASN) or descending (DECS) order based on a sort expression.

Syntax:

SELECT select_list
FROM
    table_name
ORDER BY
    sort_expression1 [ASC | DESC],
        ...
    sort_expressionN [ASC | DESC];

Example:

• Order by 1 field and ASC is default option, when we don’t mention type of odering.

SELECT * FROM public.customer ORDER BY last_name

• Order by 1 field and DESC

SELECT * FROM public.customer ORDER BY first_name DECS, last_name ASC

+ Like in condition:

We can input relative condition in our SELECT command with LIKE statement.

Example: We will all customer with their names start with ‘L’

+ INNER JOIN

INNER JOIN enables us to query data from multiple tables with INNER JOIN and SELECT keyword.

Example: In the simple database, we have the relationship between payment table and staff table

Example for 2 tables: payment and staff to query data of payment for a staff_id.

Whenever a staff sell a payment, there will a record inserted into Payment table with staff_id, amount, payment_date info.

We will query start_info include his payment that he sold.

SELECT
	staff.staff_id,
	first_name,
	last_name,
	amount,
	payment_date
FROM
	staff
INNER JOIN payment 
    ON payment.staff_id = staff.staff_id
ORDER BY payment_date;

Example: Using SQL INNER JOIN to join three tables. we have the relationship between payment table, customer_table and staff table

To join the three tables, you can do the first INNER JOIN clause and the second INNER JOIN after the fist one as the following query:

SELECT
    c.customer_id,
    c.first_name customer_first_name,
    c.last_name customer_last_name,
    s.first_name staff_first_name, 	
    s.last_name staff_last_name, 	
    amount, 	
    payment_date 
FROM customer c 
INNER JOIN payment p      
           ON p.customer_id = c.customer_id 
INNER JOIN staff s     
           ON p.staff_id = s.staff_id 
ORDER BY payment_date;

+ GROUP BY:

We’re going to group value from Select statement. We can use Group By. In the simple database, We can group data of payment table by customer_id, staff_id.

Example:

SELECT
   staff_id
FROM
   payment
Group By staff_id;

Example - GROUP BY with SUM() function:

In some cases, we expect to get the sum of payment amount that each customer has been paid.

Group by with Sum function we can do that:

SELECT
    customer_id,
 	SUM (amount)
FROM
 	payment
GROUP BY
 	customer_id;

+ INSERT STATEMENT

In order to insert a new row into a table, we can use INSERT statement with this syntax:

INSERT INTO table_name(column1, column2, …) VALUES (value1, value2, …);

We can use Insert statement to insert 1 new record into staff, In the simple database, we have 2 staff records, we will insert 3rd staff with this command

INSERT INTO public.staff (staff_id, first_name, last_name, address_id, email, store_id, active, username, password, last_update, picture) VALUES ('3','Jack','Son','5','Jack.Son@sakilastaff.com','2','t','Jack','8cb2237d0679ca88db6464eac60da96345513964','2021-05-16 16:13:11.79328','');

++ Delete:

Syntax for Delete statement:

DELETE FROM table_name WHERE condition;

We can use this statement to delete the new record that we insert before

Delete public.staff where staff_id = 3;

INCLUSION

We just learn together basic SQL commands / statement for a QA. They are very useful when we do testing.

• SEL:ECT

• INNER JOIN

• GROUP BY

• INSERT

+DELETE

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