how to check for not null column constraint in oracle sql?

Question

How do i check if a column in a table has a not null constraint in an oracle db? Can it be checked with the data dictionary?

Solution

SELECT nullable
  FROM all_tab_cols
 WHERE owner = <<owner of table>>
   AND table_name = <<name of table>>
   AND column_name = <<name of column>>

will work assuming the column is marked NOT NULL rather than, say, having a CHECK constraint that checks that it is non-NULL.

Comments

[APC]

People who use check constraints rather than column DDL to define not null columo.ns should be severely spoken to.

[Dan Lenski]

@APC, agreed, but internally Oracle represents those NOT NULL columns with check constraints. They're utterly indistinguishable from ALL_CONSTRAINTS. RRgghgh. >:-(