Predicates :: EXISTS and SINGULAR: “evolves” → “evaluates” (2x) in Note.Īltering populated tables :: Adding a non-nullable field to a populated table :: Adding a NOT NULL field: Added para + additional programlisting after first programlisting.Īltering populated tables :: Adding a non-nullable field to a populated table :: Adding a CHECKed column: Added second Note.Īltering populated tables :: Adding a non-nullable field to a populated table :: Adding a non-nullable field using domains: Renamed section to Using domains to add a non-nullable field.Īltering populated tables :: Adding a non-nullable field to a populated table :: Using domains to add a non-nullable field: Two programlistings instead of one.Īltering populated tables :: Making existing columns non-nullable :: Making an existing column NOT NULL: Added Warning.Īltering populated tables :: Making non-nullable columns nullable again: Largely rewritten, greatly extended and divided into subsections.Ĭhanging the nullability of a domain :: New top-level section.
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NULL support in Firebird SQL :: Assigning NULL: Added 4th example. What is NULL?: Added subsection NULL as a default state. Making non-nullable columns nullable again: Provisory fix of error regarding removal of NOT NULL constraints.
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* Predicates: IN, ANY, SOME, ALL, EXISTS, SINGULAR It’s not feasible to give a summary of all the changes here.Ĭonsider this a new guide with 15–25% old material. In addition, much of the existing text has been reorganised and thoroughly reworked.
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This is a major update, with so much new material added that the document has grown to around 4 times its former size. Slightly altered “Dealing with NULLs” section. Mentioned that Fb 2.0 legalises “ A = NULL” comparisons.Ĭhanged text in “Testing if something is NULL”. The exact file history is recorded in the firebird-documentation git repository see Revision History With A and B unknown, it’s impossible to know if they are equal. but you also can’t tell if MyField has a different value! If A is unknown, you can’t tell if MyField has the same value… If A is unknown, 'Home sweet ' || A is unknown. Subtract 7 and you end up with another unknown. If A is unknown, then 5 * A is also unknown. If A is unknown, then 6 + A is also unknown. Operations on null entities A and B If A and B are NULL, then: Instead, we use two entities A and B that are both NULL.Ī and B may be fields, variables, or even composite subexpressions - as long as they’re NULL, they’ll all behave the same in the enclosing expressions. In the table we don’t write NULL in the expressions (as said, this is often illegal) You can also look at the following table where per-case explanations are provided. If you have difficulty understanding why, remember that NULL means “unknown”. SINGULAR inconsistent with NULL results.UDFs returning NULL when they should return a value.UDFs returning values when they should return NULL.SELECT DISTINCT with wrong NULLS FIRST|LAST ordering.IN, = ANY and = SOME with indexed subselect.SUBSTRING results described as non-nullable.Appendix A: NULL-related bugs in Firebird.Testing for NULL and equality in practice Adding and removing domain-level CHECK constraints Making non-nullable columns nullable again Adding a CHECK constraint to an existing column Using domains to add a non-nullable field
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Adding a non-nullable field to a populated table “Upgrading” ib_udf functions in an existing database NULL non- NULL conversions you didn’t ask for