Notes for 《Teach Yourself SQL in 10 Minutes(3rd)》

What Is a Database?

a database is a collection of data stored in some organized fashion . The simplest way to think of it is to imagine a database as a filing cabinet. The filing cabinet is simply a physical location to store data, regardless of what that data is or how it is organized.

case-insensitive?

Be aware that while the SQL language is case-in sensitive, the names of tables, columns, and values may not be (that depends on your DBMS and how it is configured).

 

 

ORDER By – must be in the end

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Sorting by Multiple Columns

 

 

SELECT prod_id, prod_price, prod_name
FROM Products
ORDER BY prod_price, prod_name;

== 
SELECT prod_id, prod_price, prod_name
FROM Products
ORDER BY 2, 3;

///////////////////////////////////////////////////
ORDER BY 2, 3 means sort by prod_price and then by prod_name.
///////////////////////////////////////////////////


output:

prod_id    prod_price    prod_name
-------    ----------    --------------------
BNBG02     3.4900        Bird bean bag toy
BNBG01     3.4900        Fish bean bag toy
BNBG03     3.4900        Rabbit bean bag toy
RGAN01     4.9900        Raggedy Ann
BR01       5.9900        8 inch teddy bear
BR02       8.9900        12 inch teddy bear
RYL01      9.4900        King doll
RYL02      9.4900        Queen doll
BR03       11.9900       18 inch teddy bear

 

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ASC or DESC?

DESC is short for DESC ENDING

ASC   is short for ASCE NDING (ascending order is the default sequence)

 

 

SELECT prod_id, prod_price, prod_name
FROM Products
ORDER BY prod_price DESC, prod_name;
means:
prod_price DESC
prod_name ASC (if the DBMS assume it is default sequence)

 

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The single quotes are used to delimit a string.

 

Checking for a Range of Values

SELECT prod_name, prod_price
FROM Products
WHERE prod_price BETWEEN 5 AND 10;
//Note include 5 and 10

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Checking for No Value

SELECT prod_name
FROM Products
WHERE prod_price IS NULL;

 

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Understanding Order of Evaluation

SELECT prod_name, prod_price
FROM Products
WHERE vend_id = 'DLL01' OR vend_id = 'BRS01'
    AND prod_price >= 10;

 

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Resolve ->

         Using () in WHERE Clauses

 

 

WHERE (vend_id = 'DLL01' OR vend_id = 'BRS01')
    AND prod_price >= 10;

 

 

 

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Matching

         %   means match any number of occurrences of any character.

         _    matches just a single character. no more and no less

         []   specify a set of characters, any one of which must match a character in the specified position (the location of the wildcard).

Inner Join

 

 

 

SELECT vend_name, prod_name, prod_price
FROM Vendors, Products
WHERE Vendors.vend_id = Products.vend_id;
==
SELECT vend_name, prod_name, prod_price
FROM Vendors INNER JOIN Products
 ON Vendors.vend_id = Products.vend_id;

 

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Outer Joins

SELECT Customers.cust_id, Orders.order_num
FROM Customers LEFT OUTER JOIN Orders
 ON Customers.cust_id = Orders.cust_id;

The example uses LEFT OUTER JOIN to select 
all the rows from the table on the left in the FROM clause (the Customers table).