There are multiple NULLs in this expression, but because the first non-NULL value was reached on the third parameter, all remaining values were disregarded.Ĥ. Here is how it interprets multiple NULL values: postgres=# SELECT coalesce(null,null, 1, 2, 3, null, 4) The COALESCE function found a NULL value in the first parameter, so it continued to the second parameter, which was not NULL, so that parameter's value was returned.ģ. Here is how COALESCE works when a NULL value is the first parameter: postgres=# select coalesce (null,1,2) The COALESCE function finds the first non-NULL expression at the start, so it will always produce the same result regardless of what the remaining parameters contain.Ģ. Here is how COALESCE works with a non-NULL value for the first parameter: postgres=# select coalesce (1,null,2) It will stop evaluating parameters as soon as the first non-NULL value is reached.ġ.CASE and COALESCE can be used for similar purposes, but the advantage of using COALESCE is that it requires far less typing.Coalesce function provide similar compatibility like NVL and IFNULL which are available in other DBMS. ![]()
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