Validating null value in pl sql


When a column in a table is defined there is the possibility to have a default value for this column whenever it is inserted without a value.

CASE { simple_case_expression | searched_case_expression } [ else_clause ] END simple_case_expression expr { WHEN comparison_expr THEN return_expr }...

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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Examples: NVL2(‘A’,’B’,’C’) results in B NVL2(NULL,’B’,’C’) results in C NVL2(1,2,3) results in 2 NVL2(NULL,2,3) results in 3 Syntax: NULLIF returns NULL if expr1 is equal to expr2. Expressions must be of the same data type, There is no implicit conversion performed.

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.

LNNVL can be used in a condition when you would otherwise need to combine a condition with an IS [NOT] NULL or an NVL predicate.

The following queries have the same result: Note that the condition must be inverted when using the LNNVL function.

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