几个PLSQL FUNC的MARK

MINUS 

The MINUS query returns all rows in the first query that are not returned in the second query.

Each SQL statement within the MINUS query must have the same number of fields in the result sets with similar data types.

The syntax for an MINUS query is:

select field1, field2, . field_n
from tables
MINUS
select field1, field2, . field_n
from tables;

 DECODE

In Oracle/PLSQL, the decode function has the functionality of an IF-THEN-ELSE statement.

The syntax for the decode function is:

decode( expression , search , result [, search , result]... [, default] )

expression is the value to compare.

search is the value that is compared against expression.

result is the value returned, if expression is equal to search.

default is optional. If no matches are found, the decode will return default. If default is omitted, then the decode statement will return null (if no matches are found).

NVL

In Oracle/PLSQL, the NVL function lets you substitute a value when a null value is encountered.

The syntax for the NVL function is:

NVL( string1, replace_with )

string1 is the string to test for a null value.

replace_with is the value returned if string1 is null.