Float8 underflow

In some cases, open source PostgreSQL returns an error such asERROR: value out of range: underflow if the result of floating point mathwould be truncated to 0. Numbers too close to zero that are not representable asdistinct from zero cause an underflow error.

The PostgreSQL interface doesn't return an error in these cases;it returns the truncated 0 value instead.

concat function

In the PostgreSQL interface, theconcat() function returnsNULL if any argument is NULL. However, in open source PostgreSQL,this function ignores NULLs and returns a concatenation of all non-NULLarguments, or an empty string if all arguments are NULL. For example:

-- Returns `abcdef` in open source PostgreSQL.-- Returns NULL in the PostgreSQL interface.selectconcat('abc',NULL,'def');

The PostgreSQL interface and open source PostgreSQL haveidentical behavior for the|| operator with scalar (non-array) operands.

array_cat() function

In the PostgreSQL interface, thearray_cat() function returnsNULL if any argument is NULL. However, in open source PostgreSQL, thisfunction ignores NULLs and returns a concatenation of all non-NULL arrayarguments, or a NULL array if all arguments are NULL. The same is true for the|| operator with array operands. For example:

-- Returns `{abc, def}` in open source PostgreSQL.-- Returns NULL in the PostgreSQL interface.select '{abc}'::text[] || NULL::text[] || '{def}'::text[];

array_to_string function

In the PostgreSQL interface, thearray_to_string(array text_array, delimiter text [, null_string text ])function returns NULL if thenull_string argument is NULL. However, inopen source PostgreSQL, this function ignores the NULL arrayelements and returns a concatenation of all non-NULL elements as a stringrepresentation if thenull_string argument is NULL. For example:

-- Returns `a,b,c` in open source PostgreSQL.-- Returns NULL in the PostgreSQL interface.selectarray_to_string('{a,b,NULL,c}'::text[],',',NULL);

Object names