Validating null value in oracle sql

The constraint is checked and is guaranteed to hold for all rows.

- ENABLE NOVALIDATE means that the constraint is checked, but it does not have to be true for all rows.

However, you want to tell the user that the record is a duplicate and point them to the carbon copy. Thus you can’t just check a column thusly It will work when both source_col and test_value are NOT NULL but if they are both NULL you won’t identify the two records as being copies of each other.

Furthermore, many of the columns you check against for equivalence are NULLABLE and are of different data types (DATE, VARCHAR, NUMBER). I’ve typically handled this by having this clunky bit of logic: If you are testing against five or six records your query quickly becomes kind of ugly and difficult to visually parse so I’ve not been really happy with this technique even though it does work.

I’ve been using Oracle on and off for about twelve years so it seems like I should have known this trick already but today I learned so I’m sharing.

But you need to work with NULL values (which are no actual values).

Syntax: If expr1 contains a NULL value, then return expr3.

Examples: NULLIF(‘A’,’B’) results in A NULLIF(‘A’,’A’) results in NULL NULLIF(2,3) results in 2 NULLIF(2,2) results in NULL NULLIF(‘2’,2) results in an error NULLIF(2,’2’) results in an error Syntax: The coalesce function returns the first non-NULL value of the expressions in the list. If all expressions evaluate to NULL then NULL is returned.

Examples: COALESCE(‘A’,’B’,’C’) results in A COALESCE(NULL,’B’,’C’) results in B COALESCE(NULL, NULL,’C’) results in C COALESCE(NULL,’B’, NULL) results in B COALESCE(‘A’) results in an error Syntax: The LNNVL function is used in the WHERE clause of an SQL statement when one of the operands may contain a NULL value.

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