PostgreSQL Query data

Select all the data

SELECT * FROM table_name;

The above query will return all the rows form the table.

Select specific column from the table

SELECT column_1 , column_2 FROM table_name;

Adding aliases to column in the table

SELECT column_1 AS "alias" , column_2 AS "alias"  FROM table_name;

Example user table:

SELECT f_name AS "First name" ,l_name AS "Last name"  FROM users;

Same query you can write like this , both are same

SELECT 
f_name  "First name",
l_name  "Last name"
FROM users;

Output:

SELECT f_name ||' '|| l_name AS "Full name"  FROM users;

Sorting data in postgreSQL

We use ORDER BY keyword in order to shot the table data

Data table : 

Sort data in ascending order

SELECT * FROM customer
ORDER BY name ASC;

SELECT * FROM customer
ORDER BY name;

NOTE : ORDER BY default is ASC (ascending)

 Output : 

Sort data in descending order

SELECT * FROM customer
ORDER BY name DESC;

 Output : 

ORDER BY with alias column name

SELECT name AS Name FROM customer
ORDER BY name ASC;

 Output : 

ORDER BY with expression 

SELECT name AS Name , LENGTH(name) AS length FROM customer
ORDER BY length ASC;

 Output : 

Sort NULLS

SELECT * FROM table_name ORDER BY NILLS FIRST;

Above query will short the rows contains null in ascending order.

OUTPUT :  

SELECT * FROM table_name ORDER BY NILLS LAST;

Above query will short the rows contains null in descending order.

OUTPUT :  

SELECT * FROM table_name ORDER BY name ASC NILLS FIRST;

Above query will short the rows contains null in ascending order and shot name in ascending order .

OUTPUT :  

SELECT DISTINCT statement

SELECT DISTINCT statement returns only the distinct values , in table a column can contain multiple duplicate values , so if you want to filter the the distinct value we have to use SELECT DISTINCT

color_table : 

SELECT DISTINCT color FROM color_table;

OUTPUT :