Requesting some information

SELECT <value1>, <value2>;

It's like saying: "Hey, PostgreSQL; please can I have this returned to me?"

For example:

• SELECT 123; returns the number 123 in the results panel
• SELECT 'Hello World'; returns the text 'Hello'

Notes:

• We can execute the SQL by:
  • Clicking the play button on the toolbar at the top
  • Using the shortcut F5
• Note the semi-colons at the end of each query:
  • This tells PostgreSQL they are two separate queries
  • If these are removed and both queries are run, we would get a syntax error
  • If multiple queries are in the same session only the last query will return a result
  • To run a specific query, highlight it before executing it
• Text and Dates need to be surrounded by single-quotes (not double-quotes)
  • e.g. SELECT 'Hello World';
• Integers and Numerics can be put in as they are
  • e.g. SELECT 123;
• Multiple columns can be added by separating with commas
  • e.g. SELECT 'foo', 'bar', 42, 2.73; returns 4 columns

We can use SELECT to perform calculations with arithmetic operators

• SELECT 12 + 23; returns the number 35 "Hey, PostgreSQL; what is 12 + 23?"
• SELECT 10 * 8; returns the number 80 "Hey, PostgreSQL; what is 10 x 8?"
• SELECT 3.14 + 2.73; returns the decimal 5.87 "Hey, PostgreSQL; what is 3.14 + 2.73?"
• SELECT 56 - 23 + 12.3; returns the decimal 45.3
• SELECT 56 - (23 + 12.3); returns the decimal 20.7 (following BODMAS)

Booleans (A data type that returns true or false)

• SELECT true returns a boolean true, SELECT false returns a boolean false

Aliasing

• At the moment the column header is ?column?
• If we include the AS keyword, we can give the column a name
  • e.g. SELECT 123 AS my_number replaces ?column? with my_number (screenshot 5)
• When we query the database the column name of the table will be used by default
  • That behaviour can also be overwritten by the AS keyword