The query begins with the SELECT keyword. After it, the data we want to see in the query results are listed separated by commas.

Examples:

SELECT 258

will output the number 258

SELECT 'Elena'

will output the text Elena. Note that text must be enclosed in single quotes.

SELECT current_timestamp

but here current_timestamp without quotes. This is a variable name. The current_timestamp variable always contains the current date and time, which will be output as the result.

We can also calculate expressions:

SELECT 11*5

will output 55

SELECT 'Road ' || '60'

will output Road 60. The operator || concatenates text.

SELECT 'Road ' || 60

will give an error. Did you notice the difference? 60 is not enclosed in quotes and is treated as a number. You cannot concatenate a number to text.

SELECT 2.5

will output the number 2.5

SELECT 2,5

will output two numbers: 2 and 5. Remember that comma is a data separator?

SELECT 2, 5, 84, 3.7

will output 4 numbers

SELECT 3, 'river', 'Omsk region', current_timestamp

will output a number, two text values and a date with time.