БЛОК 3. / (15:00 - 18:30) · 2020. 5. 23. · (knjige), even if there are no matches in the...

АКАДЕМИЈА СТРУКОВНИХ СТУДИЈА ЗАПАДНА СРБИЈА

Базе података, SQL, MariaDB др Милован Миливојевић

60

БЛОК 3. / (15:00 - 18:30)

SPAJANJE TABELA: JOIN

Joining Tables with JOIN Clauses

Here is a simple example of three basic JOIN types, which you can experiment

with in order to see what the different joins accomplish:

CREATE TABLE mi1 ( a INT );

CREATE TABLE mi2 ( b INT );

INSERT INTO mi1 VALUES (1), (2), (3);

INSERT INTO mi2 VALUES (2), (4);



61

SELECT * FROM mi1 INNER JOIN mi2 ON mi1.a = mi2.b;

(INNER) JOIN: Returns records that have matching values in both tables

SELECT * FROM mi1 CROSS JOIN mi2;

A CROSS JOIN produces a result set in which every row in each table is joined to

every row in the other table; this is also called a cartesian product.

In MariaDB the CROSS keyword can be omitted, as it does nothing. Any JOIN

without an ON clause is a CROSS JOIN.



62

SELECT * FROM mi1 LEFT JOIN mi2 ON mi1.a = mi2.b;

The LEFT JOIN is an outer join, which produces a result set with all rows from the

table on the "left" (t1); the values for the columns in the other table (t2) depend on

whether or not a match was found.

If no match is found, all columns from that table are set to NULL for that row.

SELECT * FROM mi2 LEFT JOIN mi1 ON mi1.a = mi2.b;

The RIGHT JOIN is similar to the LEFT JOIN, though its resultset contains all rows

from the right table, and the left table's columns will be filled with NULLs when

needed..



63

NAPOMENA: Ako ne postiji u tabeli knjige roman DOROTEJ (izdanje 2017.)

dodati zapis za izdanje romana Dorotej iz 2017.

MariaDB [biblioteka]> INSERT INTO knjige(naslovKnjige,serijaID,autorID,godIzd)

-> VALUE

-> ("Dorotej",2,3,"2017");

Query OK, 1 row affected (0.737 sec)



64

Tekuće stanje u tabelama autori i knjige:

NAPOMENA!!!: Ako tekuće stanje u tabelama nije kao u tabelama

iznad, ažurirati tabele knjige i autori po uzoru na sledeće naredbe.

INSERT INTO autori(imeAutora, prezimeAutora, porekloAutora)

-> VALUE

-> ("Dobrica","Cosic","Srbija");

ili

UPDATE knjige SET

-> izdavacID=1,godIzd=1987,opis=" Prag, ljubav, politika..."

-> WHERE knjigaID=1;

ili

MariaDB [biblioteka]> INSERT INTO knjige(naslovKnjige, godIzd)

-> VALUE

-> ("Kad su cvetale tikve",1987);



65

Da bi mogli navesti spisak knjiga (nasloveKnjiga) po autorima, mora tablica knjiga

SPOJITI sa tablicom autora. To se moze realizovati pomocu JOIN klauzule:

Notice that the primary table from which we're drawing data is given in

the FROM clause. The table to which we're joining is given in the JOIN clause along

with the commonly named column (i.e., autorID) that we're using for the join.

U prethodnom primeru prikazani su svi autori.

Ako je potrebno prikazati samo dela Milana Kundere onda je postupak sledeci:

This statement will list the titles of Kundera books stored in the database.

Notice that we've added the AS parameter next to the column name naslovKnjige to change the

column heading in the results set to Kunderine knjige. This is known as an alias.

https://mariadb.com/kb/en/join-syntax/



66

Primer sa kompletnijim JOIN izrazom:

There are a few possible ways to construct a join.

This method works if you're using a newer version of MariaDB and if both tables

contain a column of the same name and value.

Otherwise you'll have to redo the JOIN clause to look something like this:

...

JOIN autori ON autorID = rowID

...

This excerpt is based on the assumption that the key field in the autori table is not

called autorID, but rowID instead.

There's much more that can be said about joins, but that would make for a much

longer text.

U izrazu WHERE često se, radi fleksibilnosti, koriste džoker znaci:

WHERE name_last LIKE 'Dostoevsk%'

https://mariadb.com/kb/en/join-syntax/



67

PARAMETRI u naredbi SELECT

Kao što je dato u opštem prikazu, izrazi i ključna reč SELECT imaju veliki broj

parametara. Navode se neki, koji mogu biti od koristi:

DISTINCT

KLJUČNA reč DISTINCT, se koristi kada želimo da izbegnemo duplicate u prikazu.

Na primer, ako u bazi postoji više naslova SMESNE LUBAVI od Milana Kundere ali

sa razlicitim ID brojevima (jer su različite godine i/ili izdavači), a potrebno je da se

prikaze samo spisak naslova (nezavisno od izdavača i godine izdavanja onda se

može koristiti DISTINCT.

Ako je potrebno kreirati listing sa prikazima naslova D. Nenadica, onda je sintaksa

sledeca:

Ali ako je potrebno kreirati listing sa prikazima naslova D. Nenadica, ALI BEY

PONAVLJANJA onda je sintaksa sledeca:

SELECT DISTINCT naslovKnjige,

CONCAT(imeAutora,” “,prezimeAutora) AS pisac

FROM knjige

JOIN autori USING (autorID)



68

WHERE prezimeAutora = “Nenadic”

HIGH PRIORITY

Koristi se kod baza koje su veoma opterecene UPITIMA.

SELECT DISTINCT HIGH PRIORITY naslovKnjige,


FROM knjige



ORDER BY naslovKnjige;

SQL_CALC_FOUND_ROWS

Prebrajanje broja zapisa koju su u rezultatu upita - primer

SELECT DISTINCT SQL_CALC_FOUND_ROWS naslovKnjige,


FROM knjige




69


ORDER BY naslovKnjige;



70

Primer UPITA:

MariaDB [biblioteka]> SELECT knjigaID, naslovKnjige,imeAutora,

prezimeAutora

-> FROM knjige

-> RIGHT JOIN autori ON knjige.autorID = autori.autorID

-> ORDER BY autori.autorID;

The RIGHT JOIN keyword returns all records from the right

table (autori), even if there are no matches in the left table

(knjige).

(Pitanje: Zasto u rezultatu upita ne postoji knjiga „Kad su cvetale

tikve“?)

Primer UPITA ver1:

MariaDB [biblioteka]> SELECT knjigaID, naslovKnjige,imeAutora,

prezimeAutora

-> FROM knjige

-> LEFT JOIN autori ON knjige.autorID = autori.autorID




71

The LEFT JOIN keyword returns all records from the left table

(knjige), even if there are no matches in the right table (autori).

Primer UPITA ver2:

SELECT knjigaID, naslovKnjige,imeAutora, prezimeAutora

-> FROM autori

-> LEFT JOIN knjige ON knjige.autorID = autori.autorID


OBRATITI PAZNJU: LEVI I DESNI UPIT MOGU IMATI iste REZULTATE (u zavisnosti od

rasporeda tabela LEVO/DESNO u odnosu na kljucnu rec JOIN)!

БЛОК 3. / (15:00 - 18:30) · 2020. 5. 23. · (knjige), even if there are no matches in the...

Documents