Oracle functions, connection queries, constraints

The *order by clause at the end of the SELECT statement.

Use an outer join to query data that does not meet the join criteria

With clause

character function
Lowerupperinitcap
concatsubstrlengthinstrlpad/rpadtrimreplace
number function
roundtruncmod
date
months_betweenadd_monthsnext_daylast_dayroundtrunc
general function
NVL (EXCP,EXCP)
nvl2 (EXRP,EXCP,EXCP)
nullif (EXCP,EXCP)
coalesce ( EXCP,EXCP EXCP)
if-then-else

Merge : Perform an update operation if the row that satisfies the condition exists, or else perform the insert operation:

Constraints
Constraint is a mandatory requirement for manipulating table data
There are five types of constraints:
Not NULL (can only be defined at the column level)
UNIQUE (can be defined at table-level or column-level)
PRIMARY KEY (can be defined at table-level or column-level)
FOREIGN KEY

CHECK (define the conditions that each line must meet)

Add constraint syntax
Use the ALTER TABLE statement:
Add or remove constraints, but cannot modify constraints (Add/drop)
Effective or invalid constraint (enable/disable)
Add not NULL constraint to use MODIFY statement

Oracle functions, connection queries, constraints