![]() While the expression 4 + 5 + null yields null, the sum() over those (column) values would yield 9, because aggregates ignore null values. For other cases, inserting an explicit coercion to text can be used to have non-string input accepted. The separator or a delimiter symbol will not be included at the end of the output string. x is null yields either true or false, it never yields null, so expressions using the is null or is not null operator never return null - so this is an exception to my statement above (thanks Jonathan for pointing that out).Īnother - maybe surprising - fact about null values is how they are handled by aggregate functions. The string concatenation operator ( ) will accept non-string input, so long as at least one input is of string type, as shown in Table 9.9. PostgreSQL supports various kind of aggregate function, The STRINGAGG () function is one of the aggregate function which is used to concatenate the list of strings and it will add a place to a delimiter symbol or a separator between all of the strings. But negating such an expression yields null again, not "true".īecause null is so special, the only way to check if something is null is to use the operator IS NULL or IS NOT NULL. Although in reality this has the effect of "false", but more because it's "not true", rather then false. So the comparison it's neither true nor false. This also applies to comparisons: 42 > null yields null. This is not limited to string concatenation, it also applies to computations e.g.: 42 * null returns null. The SQL standard requires any expression that involves null yields null. ![]() ![]() Should I just get used to this behavior with '||' concatenation or is this something that should be fixed? Given that, using their concat string function example: For other cases, insert an explicit coercion to text if you need to duplicate the previous behavior." A string can be of any data type char, varchar, or text. It is a standard operation built into PostgreSQL, and may. concat (, ,.) This function accepts a list of arguments that require to be convertible to a string. Concatenation is the process of combining two (or more) strings together to produce another string.However, the string concatenation operator (||) still accepts non-string input, so long as at least one input is of a string type, as shown in Table 9-6. In Postgresql, CONCAT is a function that is generally used to concatenate more than two strings except NULL explained in the arguments. Those coercions have been removed because they frequently caused surprising behaviors. "Note: Before PostgreSQL 8.3, these functions would silently accept values of several non-string data types as well, due to the presence of implicit coercions from those data types to text. Is this desired behavior? Seems weird that string concatenation with a null value would nullify the entire string. I was expecting it would otherwise return 'test'. In Postgres: select 'test' || null returns null
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