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. 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. In PostgreSQL, the CONCAT function is used to concatenate two or more strings into one. Match a POSIX regular expression against a string and returns the matching substrings.
Remove the longest string that contains specified characters from the left of the input string. So the comparison it's neither true nor false. This page provides you with the most commonly used PostgreSQL string functions that allow you to manipulate string data effectively. This also applies to comparisons: 42 > null yields null. PostgreSQL has many functions which are not defined in the standard SQL. PostgreSQL string functions take care of that for you. String formatting such as concatenation, displaying in a certain format, inserting/deleting substrings, etc., can sometimes be a tedious task. This is not limited to string concatenation, it also applies to computations e.g.: 42 * null returns null. One such category of built-in functions is the PostgreSQL string functions. 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." 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. Since version 9.1, PostgreSQL introduced a built-in string function named CONCAT to concatenate two or more strings into one. 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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