How to find the maximum value of a column in a table?

Question

PostgreSQL

The bottom line is that there is a posgresql database, it is necessary in the users database to determine the maximum value in the id field in MySQL, I ran the query SELECT MAX( id) FROM users; and everything worked now i get an empty response.

Answer 1

SELECT MAX(id) FROM users WHERE id is not null

Answer 2

I use system tables, it's more reliable and better in terms of performance

_lenght_number = ( SELECT aa.character_maximum_length FROM INFORMATION_SCHEMA.COLUMNS aa
                                 WHERE aa.table_name = TG_TABLE_NAME AND column_name = 'number' );