Statements

Base

From

I like to start with FROM because it is where we always start. We are basically wanting to process/analyze a specific set of data and that always starts with FROM. It is used to specify which table to select from that specific database from a certain project.

SELECT     column1, col2,....fields..
FROM   table_name

Select

Is usually the first command in your query, as you see above (or a long reference to a select statement). It is used to specify:

the column/field names of the table you want to select
both FROM and SELECT will get more complicated as we start nesting aggregations and conditions into them, but remember the base of all these statements

Select Distinct

Is a specific SELECT where we only choose the unique value in column(s)

In a table, a column often contains many duplicate values, and sometimes we only want the list of unique (distinct) values in that column(s)

SELECT DISTINCT     Country 
FROM                CountryTable;

Where

Is used to filter the chosen records based on a specified condition(s)

you can concatenate multiple conditions using logical operators AND, OR
narrows your query so that the database returns only the data with an exact value match or the data that matches a certain condition that you want to satisfy
WHERE is also used in UPDATE, DELETE and many other SQL commands

SELECT DISTINCT     Country 
FROM                CountryTable
WHERE               Country = "blah"
                    AND Country = "blue"
                    OR  Country = "blee";

That covers the basics of a query, now we move on and build statements with more common commands that help, sort, filter, aggregate, calculate, summarize….and many other functions I haven’t used yet.

Arrange

Command	Syntax (MySQL/DB2)	Description	Example (MySQL/DB2)
ORDER BY	`SELECT column1, column2, ... FROM table_name ORDER BY column1, column2, ... ASC\|DESC;`	`ORDER BY` keyword is used to sort the result-set in ascending or descending order. The default is ascending. In case of multiple columns in ORDER BY, the sorting will be done in the sequence of the appearance of the arguments.	`SELECT f_name, l_name, dep_id FROM employees ORDER BY dep_id DESC, l_name;` This displays the first name, last name, and department ID of employees, first sorted in descending order of department IDs and then sorted alphabetically as per their last names.

Order By Condition

just as it sounds, it sorts/orders ASC by default, always good to specify anyways
DESC has to be specified
Because it sorts in ASC order by default, it will sort alphabetically if used on character strings

SELECT     *
FROM       TableName
ORDER BY   condition 1 ASC, 
           condition 2 DESC;
# or ----
ORDER BY   condition 1 DESC, condition 2 DESC;
ORDER BY   condition 1, condition 2;     -- if you're too lazy to type DESC

several columns

just list them one after the other (as shown above) with their specific type of order you want ASC or DESC

Order By Column

We can also order by columns instead of conditions
Let’s say we use SELECT to extract 2 columns: title & pages
We know that the default sorting order is ascending
If we want to sort the results by number of pages in ascending order we use

SELECT  title, pages
FROM    book
ORDER BY pages;

# ___ OR WE CAN USE 2 THE SECOND COLUMN ON THE LIST OF SELECTED COLUMNS __
ORDER BY 2;

Assign

Aliases

Aliases are used to give a table or a column a temporary name
They make column names, calculations or aggregations more descriptive and readable
Only exist for the duration of that specific query they occupy
AS is used to create an alias, and in most languages you can skip it all together

SELECT  column_name  AS alias_name
FROM    table_name;

# ---- OR -----
SELECT  column_name(s)
FROM    table_name AS  alias_name;

Comparison Operators

>, >=, <, <=, =, !=, OR, AND

We should be familiar with these operators, there is no need to go on.