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MERGE and TRUNCATE in SQL
SQL has two more table update operators, MERGE and TRUNCATE. MERGE, like INSERT, takes a source table s and uses it to update a target table t. Briefly, a MERGE statement specifies a matching condition to determine which rows of s have at least one matching row in t (under that specified matching condition). It then specifies an open-ended series of conditions to be applied to each row of s paired with actions to be applied on t.
WHEN MATCHED AND c1 THEN x1 specifies that action x1, necessarily an UPDATE or DELETE, is to be applied on t for each matching row in s that satisfies the condition c1. WHEN NOT MATCHED AND c2 THEN x2 specifies that action x2, necessarily an INSERT, is to be applied on t for each non-matching row in s that satisfies the condition c2. The curiously named TRUNCATE statement deletes all the rows from its specified target, bypassing any triggered actions, including compensatory actions, specified for that target. The target must be a base table.
Dynamic Ranges The PL/SQL lets you determine the loop range dynamically at run time, as the example below shows: SELECT COUNT(empno) INTO emp_count FROM emp; FOR i IN 1..emp_cou
set serveroutput on declare a number(5); b number(5); c number(5); begin a:=&a; b:=&b; c:=a/b; dbms_output.put_line(c); exception when zero_d
WHEN or THEN Key Constraints Suppose a table has two columns representing a period of time throughout which the information conveyed by the other columns is recorded as having
MAX and MIN operator in SQL Example: (SELECT MAX (Mark) FROM EXAM_MARK WHERE StudentId = 'S1') (SELECT MIN (Mark) FROM EXAM_MARK WHERE StudentId = 'S1') Example
Raise_application_error - procedure of package DBMS_STANDARD , allows to issue an user_defined error messages by stored sub-program or database trigger.
Implicit Rollbacks Before execute the INSERT, UPDATE, or DELETE statement, the Oracle marks an implicit savepoint . When the statement fails, the Oracle rolls back to the save
EXIT-WHEN The EXIT-WHEN statement permits a loop to complete conditionally. Whenever the EXIT statement is encountered, the condition in the WHEN clause is computed. When the co
Example of Check Constraints Example: Workaround for when subqueries not permitted in CHECK constraints CREATE FUNCTION NO_MORE_THAN_20000_ENROLMENTS ( ) RETURNS BOOLEAN
%ROWCOUNT The %ROWCOUNT yields the number of rows affected by the INSERT, UPDATE, or DELETE statement, or returned by a SELECT INTO statement. The %ROWCOUNT yields zero when a
Naming Conventions The similar naming conventions apply to all PL/SQL program items and units including the variables, cursors, constants, cursor variables, procedures, exception
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