SQL somo la 18: Jinsi ya kutengeneza function kwenye mysql database

Wakati mwingne utahitaji kuwa na function ili kurahisisha uchakataji wa data nyingi bila ya kurudia rudia kuandika code.

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kutengeneza function tunaanza na keyword DELIMITER // hiyo utakuja tena kuiweka mwisho // DELIMITER baada ya hapo tutatumia keyword CREATE FUNCTION ikifuatiwa na jina la hiyo function ikifuatiwa na mabano (). Mfano salamu() kisha utaweka aina aina ya data na length yake ambayo hiyo function ita return katika sql function ni lazima iwe ina return data moja tu. Mfano RETURNS VARCHAR(255). kisha kama functio yako haitakuwa ikibadilikabadilika data weka keyword DETERMINISTIC hii ni option yaani sio lazima.

Baada ya hapo ndipo tutaanza kuandika code za function yetu. code hizo ni zile ambacho kuwa nini unataka kitokee. Utaanza na keyword BEGIN kisha utaweka hizo code kisha utamaliza na END.

Mwisho kumbuka kuwa ili function iweze kufanya kazi utahitaji kuitwa (call). katika mysql tutiita functionkwa kui select mfano utaiita mwishoni select salamu()

MFANO:

Tunataka kutegeneza function ambayo ita display meseji ya “haloo karibu Bongoclass”

DELIMITER //

CREATE FUNCTION salamu()

RETURNS VARCHAR(255)

DETERMINISTIC

BEGIN

RETURN 'hallo karibu Bongoclass';

END

// DELIMITER ;

SELECT salamu();

sasa inaweza kutokea ukirudia tena ku run hizo code ukaambiwa function already exist. hapo itatubidi tuifute ambayo ipo. kufuta tutatumia drop kwa mfano

DROP FUNCTION IF EXISTS salamu; nimetumia if ili kuifuta ambayo kama ipo.

Wacha tuone mfano zaidi. mfano unaofuata tutatumia database na table kutoka kwenye somo lililopita. tutakwenda kutafuta wastani wa bei.

abla hatujasonga sana una jambo nlwee sawa. ata function variable tunaztengeneza ndan ya function na tuna tuma keyword DECLARE ikifuatiwa na jina la variable ikifuatiwa na aina ya data.

Mfano

DECLARE total_price DOUBLE;

DECLARE total_count INT;

Kisha ili kuweza kuweka value kwenye variable tutatumia select into na sio from tunatumia into kwa kuwa tunataka kuingiza data kwenye variable.

Mfano:

SELECT SUM(price) INTO total_price FROM products;

SELECT COUNT(*) INTO total_count FROM products;

Mwisho utatumia keyword RETURN ili ku return data ambazo nio output ya function yako.

Mfano:

DROP FUNCTION IF EXISTS wastani;

DELIMITER //

CREATE FUNCTION wastani()

RETURNS DOUBLE

DETERMINISTIC

BEGIN

DECLARE total_price DOUBLE;

DECLARE total_count INT;

-- Calculate the total price of all products

SELECT SUM(price) INTO total_price FROM products;

-- Calculate the total number of products

SELECT COUNT(*) INTO total_count FROM products;

-- Calculate and return the average price, handle division by zero

IF total_count > 0 THEN

RETURN ROUND(total_price / total_count, 2);

ELSE

RETURN 0;

END IF;

END //

DELIMITER ;

SELECT wastani()

Mwisho:

katika somo linalofuata tutakwenda kujifunza kuhusu stored procedure kwenye mysl na jinsi inavyotofautiana na function

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Author: Rajabu

Tarehe: 1970-01-01 03:33:44 Topic: Database Main: ICT File: Download PDF Views 503

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