![]() ![]() This obviously prevents us from adding the same value more than once:ĮRROR: duplicate key value violates unique constraint "i"īut what about NULLs? NULL means undefined, so what should the unique index do when you try to insert more than one row with the value of NULL? Are two NULL values the same or not? If you ask PostgreSQL if NULL equals NULL, you get undefined (or NULL):Ĭomparing something which is not defined against something which is not defined does not make much sense. Null is returned only if all arguments are null. Postgres=# create unique index i on t ( a ) 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. To replace the null values with some default values, you must use the IS NULL operator with the UPDATE query as follows: UPDATE tablename SET columnname. What is it about? The answer is quite easy if we do a little example which shows the effect of this new feature.Ĭonsider the following table and unique index: ![]() It is very important to understand that a NULL value is different from a zero value or a field that contains spaces. To insert a NULL value into a PostgreSQL database table column using PHP, you can use the NULL keyword in your INSERT query. ![]() A field with a NULL value is a field with no value. NULL NULL results in NULL, as opposed to, which evaluates to TRUE. In PostgreSQL, COALESCE() function allows to return an. Finding the size or length of NULL results in NULL. The NULL function can be used to provided alternate value of a column if it contains NULL value. A NULL value in a table is a value in a field that appears to be blank. It doesn’t have a value, as opposed to an empty string, which is a value but an empty one. Another nice feature was just committed for PostgreSQL 15: Add UNIQUE null treatment option (discussion here, commit details here). The PostgreSQL NULL is the term used to represent a missing value. ![]()
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