Professor: Dr. Shu-Ching Chen TA: Hsin-Yu Ha Function, Trigger used in PosgreSQL

What are stored procedures A subroutine available to applications that access a relational database system. PL/pgSQL : A loadable procedural language. Creates functions and trigger procedures Adds control structures Performs complex computation Inherits all user-defined types, functions Can be defined to be trusted by the server Easy to use

Why do we need stored procedure One Query Wait, receive, process/compute Database Server Internet Reduce roundtrips across the network Can make security easier to manage Are precompiled

Structure of PL/pgSQL

Declarations (1) Declaring PL/pgSQL variable

Declarations (2) Declaring PL/pgSQL variable and assigning values

Declarations (3) Declaring Function Parameters (1) directly give a name to the parameter in the command (2) name ALIAS FOR $n;

Declarations (4) Directly using argument variables

Declarations (5) Attributes %TYPE attribute

Declarations (6) Attributes %ROWTYPE attribute

Comment syntax Single-line comments Block comments

Basic Statements (1) Assignment Executing a Command with NO RESULT – PERFORM

Basic Statements (2) Executing a Command with a Single-row result

Basic Statements (3) Example

Basic Statements (4)

Basic Statements (5) FOUND – Boolean variable

Control Structures(1) RETURN expression

Control Structures(2) IF statements IF … THEN IF … THEN … ELSE IF … THEN … ELSIF … THEN … ELSE

Control Structures(3) CASE statements CASE … WHEN … THEN … ELSE … END CASE CASE WHEN … THEN … ELSE … END CASE

Control Structures(4) LOOP EXIT

Control Structures(5) CONTINUE WHILE

Control Structures(6) FOR (Integer Variant)

Control Structures(7) FOR (Looping through query results)

Control Structures(8) Trapping Errors appendix.html#ERRCODES-TABLE appendix.html#ERRCODES-TABLE

Trigger(1) Triggers that are specified to fire INSTEAD OF the trigger event must be marked FOR EACH ROW, and can only be defined on views. BEFORE and AFTER triggers on a view must be marked as FOR EACH STATEMENT. before constraints are checked and the INSERT, UPDATE, or DELETE is attempted after constraints are checked and the INSERT, UPDATE, or DELETE has completed in the case of inserts, updates or deletes on a view

Trigger(2) Triggers that are specified to fire INSTEAD OF the trigger event must be marked FOR EACH ROW, and can only be defined on views. BEFORE and AFTER triggers on a view must be marked as FOR EACH STATEMENT.

Trigger(3) In row-level triggers the WHEN condition can examine the old and/or new values of columns of the row. Statement-level triggers can also have WHEN conditions, although the feature is not so useful for them since the condition cannot refer to any values in the table. SELECT does not modify any rows so you cannot create SELECT triggers. Rules and views are more appropriate in such cases.

Trigger(4) Execute the function check_account_update whenever a row of the table accounts is about to be updated: The same, but only execute the function if column balance is specified as a target in the UPDATE command: This form only executes the function if column balance has in fact changed value:

Trigger(5) Call a function to log updates of accounts, but only if something changed: Execute the function view_insert_row for each row to insert rows into the tables underlying a view:

Trigger(6) DROP TRIGGER removes an existing trigger definition.: ALTER TRIGGER changes properties of an existing trigger. The RENAME clause changes the name of the given trigger without otherwise changing the trigger definition.

Trigger(7) One built in trigger function, suppress_redundant_updates_trigger, which will prevent any update that does not actually change the data in the row from taking place, in contrast to the normal behaviour which always performs the update regardless of whether or not the data has changed. The suppress_redundant_updates_trigger function can be added to a table like this:

Cursors (1) Declaring Cursor Variables OPEN FOR query

Cursors (2) Using Cursors FETCH MOVE NEXT PRIOR FIRST LAST ABSOLUTE count RELATIVE count FORWARD BACKWORD

Cursors (3) Using Cursors CLOSE Returning Cursor

Cursors (4) Looping Through a Cursor’s Result

Errors and Messages RAISE Example

Reference PostgreSQL Manuals PostgreSQL Practical PostgreSQL

Stored Procedure in PgAdmin 1 2 3