MySql ya mwaka upi unatumia, na front end unatumia ipi?
coz wakati mwingine inategemeana na version ipi unatumia ya MySql vs front end.
tukija kwenye jinsi ya kutumia EXISTS:
SELECT *
FROM klienci
WHERE EXISTS (
SELECT adres
FROM klienci
WHERE id = '1'
)
kwanza kabisa hii query itaanza kua executed kwenye mabano:
(
SELECT adres
FROM klienci
WHERE id = '1'
)
then baada ya kuona kwamba query inareturn rows ndio itakwenda kwenye EXISTS condition.
kwamfano ikiwa query hii ikakupa result, then EXISTS condition itakua executed na itareturn rows zote kutoka kwenye table ya klienci.
kwamahesabu ya haraka haraka nadhani utakua umekosea kwenye datatype. naitilia mashaka hiyo column ya id, inaweza ikawa umedeclare as integer lakini hapa umeandika as 'varchar' cheki hapa: WHERE id = '1'
hebu jaribu kutumia hizi data hapa chini kwenye mysql yako kisha unijuze kama umepata result ama vipi, nimejaribu kutumia simple query inayofanana na yako.
ukipata result then jaribu kucompare na query yako uone tatizo likwapi.
JUST COPY AND PASTE INTO QUERY ANALZER AND RUN IT.
CREATE TABLE Books
(
BookID SMALLINT NOT NULL PRIMARY KEY,
BookTitle VARCHAR(60) NOT NULL,
Copyright varchar(10)
)
INSERT INTO Books VALUES (12786, 'Java',1934)
INSERT INTO Books VALUES (13331, 'MySQL',1919)
INSERT INTO Books VALUES (14356, 'PHP',1966)
INSERT INTO Books VALUES (15729, 'PERL',1932)
INSERT INTO Books VALUES (16284, 'Oracle',1996)
INSERT INTO Books VALUES (17695, 'Pl/SQL',1980)
INSERT INTO Books VALUES (19264, 'JavaScript',1992)
INSERT INTO Books VALUES (19354, 'Vb.NET', 1993)
RKisha malizia kwa run hii query hapa chini
SELECT *
FROM books
WHERE EXISTS (
SELECT bookid
FROM books
WHERE bookid = 12786
)