![]() ![]() ![]() All of these are folded to n spaces in char(n) per definition of the type. In char(n) an empty string is not different from any other string consisting of only spaces. In most situations text or character varying should be used instead.ĭo not confuse char(n) with other, useful, character types varchar(n), varchar, text or "char" (with double-quotes). ( char / character are short for char(1) / character(1).) Its use is discouraged in Postgres: This is about the data type char(n), short for: character(n). If the expression is row-valued, then IS NULL is true when the row expression itself is null or when all the rows fields are null, while IS NOT NULL is true. coalesce(stringexpression, '') = ''īut the expressions at the top are faster.Īsserting the opposite is even simpler: " stringexpression is neither null nor empty": stringexpression '' Null is returned only if all arguments are null. They will interchangeably accept character varying arguments. 2 Answers Sorted by: 19 Use max (coalesce (logincount, 0)) to avoid NULLs According to Postgres docs (9.6): The COALESCE function returns the first of its arguments that is not null. Except where noted, these functions and operators are declared to accept and return type text. Strings in this context include values of the types character, character varying, and text. Or use your original expression without trim(), which is costly noise for char(n) (see below), or incorrect for other character types: strings consisting of only spaces would pass as empty string. This section describes functions and operators for examining and manipulating string values. ![]() Works for any character type including char(n). Or the reverse approach (may be easier to read): (stringexpression '') IS NOT TRUE This PostgreSQL IS NULL example will insert records into the contacts table where the employeenumber contains a NULL value. So to check for: " stringexpression is either null or empty": (stringexpression = '') IS NOT FALSE All the remaining arguments from the first non-null argument are not evaluated. The COALESCE function evaluates arguments from left to right until it finds the first non-null argument. for '' (or for any string consisting of only spaces with the data type char(n)) If all arguments are null, the COALESCE function will return null. The expression stringexpression = '' yields: ![]()
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