Principles of Database Systems (Chapter 5: Database Programming)

First, stored procedures

The concept : A stored procedure is a group in order to complete a specific feature set of SQL statements, and its essence is a piece of code stored in the database. It can consist of declarative and procedural sql statement sql statement.

Features:

SQL language can enhance the functionality and flexibility
Good encapsulation
high performance
You can reduce network traffic
It can be used as a security mechanism to ensure the integrity of the database and data security

User-defined terminator ( ELIMITER )

ELimit $$:
Example: The MySQL terminator changed to two exclamation marks "!!" (DELIMITER !!)

Create a stored procedure using the CREATE PROCEDURE statement: CREATE PROCEDURE the SP_NAME ([proc_parameter [, ...]]) routine_body;

proc_paramete: parameter list specifies the stored procedure

routine_body: a body portion stored procedure, also referred to as body of the procedure

[IN | OUT | INOUT] param_name type: parameter name, parameter types

For example: create a stored procedure in mysql_test used to implement a given table customers in a customer id number customers can modify a table in the customer's gender as a specific gender

Use the DECLARE statement to declare local variables: DECLARE var_name [, ...] of the type [the DEFAULT value]

For example: declare a local variable integer cid: DECLARE cid INT (10);

Use DECLARE statement to declare local variables

1) Only BEGIN statement in the stored procedure body ... END statement block;
2) must be declared at the beginning of the stored procedure;
3) its scope is limited to the statement BEGIN ... END statement block;
4) different from the user variable

Local variables and user variables difference:

1) local variable declarations, not in front of the @ sign, and it can be declared only its BEGIN ... END statement block statement used;
2) When you declare a variable user will use the @ symbol in front of its name, user variables declared simultaneously exist in the entire session.

Use of local variable SET statement: SET var_name = expr [, var_name = expr] ... SET CID = 910;

SELECT ... INTO statement using the value of the selected columns directly into a local variable

Flow control statements

1, conditional statement IF ... THEN ... ELSE statement CASE statements (IF condition THEN expression the ELSE expression 1 2 END IF;)
2, loop LOOP statement WHILE statement REPEAT statement

WHILE END WHILE conditional expression

repeat expression END repeat

loop expression END loop

ITERATE statement that out of the current cycle

**************************** cursor CURSOR ******************** *********************

Create a cursor using the DECLARE CURSOR statement

Use the OPEN statement to open a cursor: OPEN cursor_name

Use FETCH ... INTO statement read data:

Close the cursor, using the CLOSE statement: CLOSE cursor_name

************************ ********************** use stored procedures

Use the CALL statement to call a stored procedure

Sp_update_sex call a stored procedure in the database mysql_test, customer id number 909 modified male sex customers "M"

CALL sp_update_sex(909,’M’);

DROP PROCEDURE statement to remove the use of stored procedures

DROP PROCEDURE[IF EXISTS] sp_name

Second, memory function

Stored function with a stored procedure, an SQL statement is the code fragment and a procedural statements of

Creating stored functions using the CREATE FUNCTION statement

CREATE FUNCTION sp_name([func_parameter[,…]]) RETURNS type routine_body

sp_name: Specifies the name of the stored function
func_parameter: parameter specifies the storage function
RETURNS type: declare function returns the type of data stored value; type specifies the data type of the return value
Body portion routine_body specified storage function, also called memory function body

Mysql_test created in the database in a storage function, the function can be based on the requirements of a given customer id number returns the customer's gender, if the database is not given customer id number, then return "is not the client."

Use mysql_test;
DELIMITER $$
CREATE FUNCTION fn_search(cid INT)
RETURNS CHAR(20)
DETERMINISTIC
BEGIN
DECLARE SEX CHAR(20);
SELECT cust_sex INTO SEX FROM customers
 WHERE cust_id=cid;
IF SEX IS NULL THEN
RETURN(SELECT’没有该客户’);
ELSE IF SEX=‘F’ THEN
RETURN(SELECT’女’);
 ELSE RETURN(SELECT ‘男’);
 END IF;
 END IF;
END $$

Use the keyword SELECT call a stored function: SELECT the SP_NAME ([func_parameter [, ...]])

Use DROP FUNCTION statement removes the stored function: DROP FUNCTION [IF EXISTS] the SP_NAME