How to find if letter exist in string SQL - sql

Question

DROP TABLE IF EXISTS t_z_ksiazka CASCADE;
DROP TABLE IF EXISTS t_a_ksiazki CASCADE;
DROP TABLE IF EXISTS t_ksiazka CASCADE;
DROP TABLE IF EXISTS t_zamowienie CASCADE;
DROP TABLE IF EXISTS t_autor CASCADE;
DROP TABLE IF EXISTS t_wydawca CASCADE;
DROP TABLE IF EXISTS t_klient CASCADE;
DROP TABLE IF EXISTS t_dostawca CASCADE;
CREATE TABLE t_ksiazka(
ISBN int2 PRIMARY KEY,
tytul varchar(40),
wydawca int2,
rok varchar(4),
oprawa varchar(10),
dostawca int2,
cena decimal(4,2),
ilosc int2
);
CREATE TABLE t_autor (
id_autora int2 PRIMARY KEY,
imie varchar(40),
nazwisko varchar(40)
);
CREATE TABLE t_a_ksiazki (
id_autora int2,
ISBN int2
);
ALTER TABLE t_a_ksiazki ADD CONSTRAINT klucz PRIMARY KEY (id_autora, ISBN);
ALTER TABLE t_a_ksiazki ADD CONSTRAINT klucz_od_ksiazki FOREIGN KEY (ISBN)
REFERENCES t_ksiazka(ISBN) ON DELETE CASCADE;
ALTER TABLE t_a_ksiazki ADD CONSTRAINT klucz_od_autora FOREIGN KEY (id_autora)
REFERENCES t_autor(id_autora) ON DELETE CASCADE ;
CREATE TABLE t_wydawca (
id_wydawcy int2 PRIMARY KEY,
nazwa varchar(10),
adres varchar(40)
);
ALTER TABLE t_ksiazka ADD CONSTRAINT klucz_od_wydawcy FOREIGN KEY (wydawca)
REFERENCES t_wydawca(id_wydawcy) ON DELETE CASCADE ;
CREATE TABLE t_zamowienie (
id_zam int2 primary key,
id_klienta int2,
data_Zam DATE,
karta int2,
zrealizowane int2
);
CREATE TABLe t_z_ksiazka (
id_zam int2,
isbn int2,
data_Wys DATE,
ilosc int2
);
CREATE TABLE t_klient(
id_klienta int2 PRIMARY KEY,
imie varchar(30),
nazwisko varchar(40),
ulica varchar(30),
miasto varchar(30),
wojewodztwo varchar(30),
kod varchar(30),
telefon varchar(30)
);
ALTER TABLE t_zamowienie ADD CONSTRAINT klucz_od_klienta FOREIGN KEY(id_klienta) REFERENCES
t_klient(id_klienta) ON DELETE CASCADE;
ALTER TABLE t_z_ksiazka ADD CONSTRAINT klucz_od_zamowienia FOREIGN KEY(id_zam) REFERENCES
t_zamowienie(id_zam) ON DELETE CASCADE;
CREATE TABLE t_dostawca (
id_dostawcy int2 PRIMARY KEY,
nazwa varchar(30),
ulica varchar(30),
miejscowosc varchar(30),
wojewodztwo varchar(40),
kod varchar(15),
telefon varchar(15)
);
ALTER TABLE t_z_ksiazka ADD CONSTRAINT klucz_z_ksiazki FOREIGN KEY(isbn) REFERENCES
t_ksiazka(ISBN) ON DELETE CASCADE;
ALTER TABLE t_ksiazka ADD CONSTRAINT klucz_z_dostawcy FOREIGN KEY(dostawca) REFERENCES
t_dostawca(id_dostawcy) ON DELETE CASCADE;
INSERT into t_autor VALUES (1, 'Joseph', 'Heller');
INSERT into t_autor VALUES (2, 'Patrick', 'Suskind');
INSERT into t_autor VALUES (3, 'Ryszard', 'Kapuscinski');
INSERT into t_autor VALUES (4, 'Milan', 'Kundera');
INSERT into t_autor VALUES (5, 'Pawel', 'Huelle');
INSERT into t_autor VALUES (6, 'Maria', 'Heller');
INSERT into t_autor VALUES (7, 'Patrick', 'Nieznany');
INSERT into t_autor VALUES (8, 'Ryszard', 'Kapuscinski');
INSERT into t_autor VALUES (9, 'Adam', 'Mickiewicz');
INSERT into t_autor VALUES (10, 'Henryk', 'Sienkiewicz');
INSERT into t_autor VALUES (11, 'Jozef', 'Wybicki');
INSERT into t_autor VALUES (12, 'Cyprian', 'Norwid');
INSERT into t_autor VALUES (13, 'Wincenty', 'Witos');
INSERT into t_autor VALUES (14, 'Milan', 'Kundera');
INSERT into t_autor VALUES (15, 'Pawel', 'Wspolczesny');
INSERT into t_autor VALUES (16, 'Ryszard', 'Mazur');
INSERT into t_autor VALUES (17, 'Beata', 'Powstaniec');
INSERT into t_autor VALUES (18, 'Dariusz', 'Port');
INSERT into t_autor VALUES (19, 'Wiktor', 'Porto');
INSERT into t_autor VALUES (20, 'Pawel', 'Wllman');
INSERT into t_autor VALUES (21, 'Maria', 'Kuncewiczowa');
INSERT into t_autor VALUES (22, 'Jan', 'Zamoyski');
INSERT into t_autor VALUES (23, 'Marian', 'Zamoyski');
INSERT into t_autor VALUES (24, 'Adam', 'Zielony');
INSERT into t_autor VALUES (25, 'Henryk', 'Wolski');
INSERT into t_autor VALUES (26, 'Juliusz', 'Cezar');
INSERT into t_autor VALUES (27, 'Maria', 'Konopnicka');
INSERT into t_autor VALUES (28, 'Tadeusz', 'Rozewicz');
INSERT into t_autor VALUES (29, 'Juliusz', 'Slowacki');
INSERT into t_autor VALUES (30, 'Pawel', 'Wierny');
INSERT into t_dostawca VALUES (1, 'Goniec', 'Wiejska', 'B-stok', 'Podlaskie', '15-351', '85-7444-555');
INSERT into t_dostawca VALUES (2, 'UPS', 'sucha', 'Lublin', 'lubelskie', '22-100', '85-7444-555');
INSERT into t_dostawca VALUES (3, 'Konik', 'miejska', 'Opole', 'opolskie', '31-100', '85-7444-555');
INSERT into t_dostawca VALUES (4, 'Pociag', 'nowa', 'Gdansk', 'pomorskie', '10-200', '85-7444-555');
INSERT into t_dostawca VALUES (5, 'Poczta', 'srebrna', 'K-owice', 'slaskie', '41-000', '85-7444-555');
INSERT into t_dostawca VALUES (6, 'Stolica', 'zlota', 'Wa-wa', 'mazowieckie', '00-950', '85-7444-555');
INSERT into t_dostawca VALUES (7, 'Kelner', 'wysockiego', 'Cz-wa', 'slaskie', '42-200', '85-7444-555');
INSERT into t_wydawca VALUES (1, 'Czytelnik', 'W-wa');
INSERT into t_wydawca VALUES (2, 'PIW', 'W-wa');
INSERT into t_wydawca VALUES (3, 'Znak', 'W-wa');
INSERT into t_wydawca VALUES (4, 'Helion', 'Wroclaw');
INSERT into t_wydawca VALUES (5, 'Robomatic', 'Wroclaw');
INSERT into t_wydawca VALUES (6, 'Znak', 'Cz-wa');
INSERT into t_ksiazka VALUES (1, 'Kontrabasista', 1, '1997', 'twarda', 1, 20, 5);
INSERT into t_ksiazka VALUES (2, 'Mercedes Benz', 3, '2001', 'twarda', 2, 30, 5);
INSERT into t_ksiazka VALUES (3, 'Tozsamosc', 2, '1998', 'miekka', 3, 20, 4);
INSERT into t_ksiazka VALUES (4, 'Cesarz', 1, '1978', 'twarda', 4, 25, 2);
INSERT into t_ksiazka VALUES (5, 'Lapidarium', 1, '1995', 'twarda', 5, 35 , 2);
INSERT into t_ksiazka VALUES (6, 'Pan Tadeusz', 4, '1997', 'twarda', 6, 20, 5);
INSERT into t_ksiazka VALUES (7, 'Potop', 5, '2001', 'twarda', 7, 30, 5);
INSERT into t_ksiazka VALUES (8, 'mazurek dabrowskiego', 6, '1998', 'miekka', 1, 20, 4);
INSERT into t_ksiazka VALUES (9, 'fortepian chopina', 6, '1978', 'twarda', 2, 25, 2);
INSERT into t_ksiazka VALUES (10, 'pole dla wszystkich', 5, '1995', 'twarda', 3, 35 , 2);
INSERT into t_ksiazka VALUES (11, 'stol', 4, '1997', 'twarda', 4, 20, 5);
INSERT into t_ksiazka VALUES (12, 'krzeslo', 3, '2001', 'twarda', 5, 30, 5);
INSERT into t_ksiazka VALUES (13, 'drukarka', 2, '1998', 'miekka', 6, 20, 4);
INSERT into t_ksiazka VALUES (14, 'aparaty cyfrowe', 1, '1978', 'twarda', 7, 25, 2);
INSERT into t_ksiazka VALUES (15, 'nibelung', 6, '1995', 'twarda', 1, 35 , 2);
INSERT into t_ksiazka VALUES (16, 'Pan samochodzik', 1, '2007', 'miekka', 1, 20, 5);
INSERT into t_ksiazka VALUES (17, 'Mlode wilki', 3, '2001', 'twarda', 2, 30, 5);
INSERT into t_ksiazka VALUES (18, 'Tosca', 2, '1998', 'miekka', 3, 20, 4);
INSERT into t_ksiazka VALUES (19, 'Winetoo', 1, '1978', 'twarda', 4, 25, 2);
INSERT into t_ksiazka VALUES (20, 'Stawka wieksza niz zycie', 1, '1995', 'twarda', 5, 35 , 2);
INSERT into t_ksiazka VALUES (21, 'Czterej pancerni bez psa', 4, '1997', 'twarda', 6, 20, 5);
INSERT into t_ksiazka VALUES (22, 'Egzorcysta', 5, '2001', 'twarda', 7, 30, 5);
INSERT into t_ksiazka VALUES (23, 'himalaje', 6, '1998', 'miekka', 1, 20, 4);
INSERT into t_ksiazka VALUES (24, 'nibylandia', 6, '1978', 'twarda', 2, 25, 2);
INSERT into t_ksiazka VALUES (25, 'ostatni mohikanin', 5, '1995', 'twarda', 3, 35 , 2);
INSERT into t_ksiazka VALUES (26, 'ostatni most', 4, '1997', 'twarda', 4, 20, 5);
INSERT into t_ksiazka VALUES (27, 'w samo poludnie', 3, '2001', 'twarda', 5, 30, 5);
INSERT into t_ksiazka VALUES (28, 'powrot do przeszlosci', 2, '1998', 'miekka', 6, 20, 4);
INSERT into t_ksiazka VALUES (29, 'samo zycie', 1, '1978', 'twarda', 7, 25, 2);
INSERT into t_ksiazka VALUES (30, 'klan', 6, '1995', 'twarda', 1, 35 , 2);
INSERT into t_ksiazka VALUES (31, 'm jak milosc', 1, '1997', 'twarda', 1, 20, 5);
INSERT into t_ksiazka VALUES (32, 'bez szans', 3, '2001', 'twarda', 2, 30, 5);
INSERT into t_ksiazka VALUES (33, 'ksiega zakazana', 2, '1998', 'miekka', 3, 20, 4);
INSERT into t_ksiazka VALUES (34, 'Byle do przodu', 1, '1978', 'twarda', 4, 25, 2);
INSERT into t_ksiazka VALUES (35, 'Nic na sile', 1, '1995', 'twarda', 5, 35 , 2);
INSERT into t_ksiazka VALUES (36, 'Anakonda', 4, '1997', 'twarda', 6, 20, 5);
INSERT into t_ksiazka VALUES (37, 'amok', 5, '2001', 'twarda', 7, 30, 5);
INSERT into t_ksiazka VALUES (38, 'koko koko euro spoko', 6, '1998', 'miekka', 1, 20, 4);
INSERT into t_ksiazka VALUES (39, 'na ludowo', 6, '1978','twarda', 2, 25, 2);
INSERT into t_ksiazka VALUES (40, 'K-11', 5, '1995', 'twarda', 3, 35 , 2);
INSERT into t_ksiazka VALUES (41, 'Szczyt', 4, '1997', 'twarda', 4, 20, 5);
INSERT into t_ksiazka VALUES (42, 'piknik pod wiszaca skala', 3, '2001', 'twarda', 5, 30, 5);
INSERT into t_ksiazka VALUES (43, 'killer', 2, '1998', 'miekka', 6, 20, 4);
INSERT into t_ksiazka VALUES (44, 'madagaskar', 1, '1978', 'twarda', 7, 25, 2);
INSERT into t_ksiazka VALUES (45, 'niebo', 6, '1995', 'twarda', 1, 35 , 2);
INSERT into t_a_ksiazki VALUES(2, 1);
INSERT into t_a_ksiazki VALUES(5, 2);
INSERT into t_a_ksiazki VALUES(4, 3);
INSERT into t_a_ksiazki VALUES(3, 4);
INSERT into t_a_ksiazki VALUES(2, 5);
INSERT into t_a_ksiazki VALUES(9, 6);
INSERT into t_a_ksiazki VALUES(10, 7);
INSERT into t_a_ksiazki VALUES(11, 8);
INSERT into t_a_ksiazki VALUES(12, 9);
INSERT into t_a_ksiazki VALUES(5, 10);
INSERT into t_a_ksiazki VALUES(4, 11);
INSERT into t_a_ksiazki VALUES(3, 12);
INSERT into t_a_ksiazki VALUES(2, 13);
INSERT into t_a_ksiazki VALUES(5, 14);
INSERT into t_a_ksiazki VALUES(4, 15);
INSERT into t_a_ksiazki VALUES(2, 31);
INSERT into t_a_ksiazki VALUES(5, 32);
INSERT into t_a_ksiazki VALUES(4, 33);
INSERT into t_a_ksiazki VALUES(15, 34);
INSERT into t_a_ksiazki VALUES(16, 35);
INSERT into t_a_ksiazki VALUES(17, 36);
INSERT into t_a_ksiazki VALUES(19, 37);
INSERT into t_a_ksiazki VALUES(19, 38);
INSERT into t_a_ksiazki VALUES(11, 39);
INSERT into t_a_ksiazki VALUES(25, 40);
INSERT into t_a_ksiazki VALUES(24, 41);
INSERT into t_a_ksiazki VALUES(23, 42);
INSERT into t_a_ksiazki VALUES(22, 43);
INSERT into t_a_ksiazki VALUES(25, 44);
INSERT into t_a_ksiazki VALUES(24, 45);
INSERT into t_a_ksiazki VALUES(22, 16);
INSERT into t_a_ksiazki VALUES(25, 17);
INSERT into t_a_ksiazki VALUES(14, 18);
INSERT into t_a_ksiazki VALUES(13, 19);
INSERT into t_a_ksiazki VALUES(12, 20);
INSERT into t_a_ksiazki VALUES(19, 21);
INSERT into t_a_ksiazki VALUES(30, 22);
INSERT into t_a_ksiazki VALUES(21, 23);
INSERT into t_a_ksiazki VALUES(12, 24);
INSERT into t_a_ksiazki VALUES(15, 25);
INSERT into t_a_ksiazki VALUES(14, 26);
INSERT into t_a_ksiazki VALUES(23, 27);
INSERT into t_a_ksiazki VALUES(22, 28);
INSERT into t_a_ksiazki VALUES(15, 29);
INSERT into t_a_ksiazki VALUES(14, 30);
INSERT into t_klient VALUES (1, 'Jan', 'Kowalski', 'Wiejska', 'W-wa', 'mazowieckie', '00-480', '624-45-56');
INSERT into t_klient VALUES (2, 'Tadeusz', 'Malinowski', 'Nowy Swiat', 'W-wa', 'mazowieckie', '00-480', '624-42-33');
INSERT into t_klient VALUES (3, 'Krystyna', 'Torbicka', 'Krakowska', 'W-wa', 'mazowieckie', '00-480', '624-22-11');
INSERT into t_klient VALUES (4, 'Anna', 'Marzec', 'Suraska', 'B-stok', 'podlaskie', '15-333', '744-34-34');
INSERT into t_klient VALUES (5, 'Adam', 'Kepinski', 'Lipowa', 'B-stok', 'podlaskie', '15-356', '756-34-33');
INSERT into t_zamowienie VALUES(1, 1, '2007-01-10', 1,1);
INSERT into t_zamowienie VALUES(2, 2, '2004-01-10', 1,0);
INSERT into t_zamowienie VALUES(3, 3, '2003-01-10', 0,0);
INSERT into t_zamowienie VALUES(4, 2, '2002-01-11', 0,0);
INSERT into t_zamowienie VALUES(5, 4, '2001-01-11', 1,1);
INSERT into t_zamowienie VALUES(6, 5, '2008-01-11', 1,1);
INSERT into t_zamowienie VALUES(7, 4, '2007-10-12', 1,1);
INSERT into t_zamowienie VALUES(8, 4, '2010-01-12', 1,0);
INSERT into t_zamowienie VALUES(9, 3, '2011-01-12', 0,0);
INSERT into t_zamowienie VALUES(10, 5, '2012-01-12', 0,0);
INSERT into t_zamowienie VALUES(11, 4, '2012-04-12', 1,1);
INSERT into t_zamowienie VALUES(12, 1, '2012-05-12', 1,1);
INSERT into t_z_ksiazka VALUES(1, 1, '2008-01-11', 1);
INSERT into t_z_ksiazka VALUES(1, 2, '2008-01-11', 1);
INSERT into t_z_ksiazka VALUES(1, 3, '2008-01-11', 1);
INSERT into t_z_ksiazka VALUES(2, 3, '2004-01-11', 1);
INSERT into t_z_ksiazka VALUES(2, 4, '2004-01-11', 2);
INSERT into t_z_ksiazka VALUES(3, 1, '2003-01-11', 1);
INSERT into t_z_ksiazka VALUES(4, 2, '2002-01-12', 1);
INSERT into t_z_ksiazka VALUES(4, 5, '2002-01-12', 2);
INSERT into t_z_ksiazka VALUES(5, 5, '2001-01-12', 1);
INSERT into t_z_ksiazka VALUES(5, 4, '2001-01-12', 1);
INSERT into t_z_ksiazka VALUES(6, 15, '2008-01-12', 2);
INSERT into t_z_ksiazka VALUES(7, 11, '2007-01-12', 1);
INSERT into t_z_ksiazka VALUES(8, 12, '2010-01-13', 1);
INSERT into t_z_ksiazka VALUES(9, 13, '2011-01-13', 1);
INSERT into t_z_ksiazka VALUES(9, 3, '2011-01-13', 1);
INSERT into t_z_ksiazka VALUES(9, 4, '2011-01-13', 2);
INSERT into t_z_ksiazka VALUES(10, 10, '2012-01-13', 1);
INSERT into t_z_ksiazka VALUES(11, 7, '2012-04-13', 1);
INSERT into t_z_ksiazka VALUES(11, 5, '2012-04-13', 2);
INSERT into t_z_ksiazka VALUES(12, 5, '2012-05-13', 1);
INSERT into t_z_ksiazka VALUES(12, 8, '2012-05-13', 1);
INSERT into t_z_ksiazka VALUES(12, 9, '2012-05-13', 2);
Search for the name of those authors whose last name is anywhere the same letter as the first letter of the surname author with ID 26.
I was thinking to create a subquery and I come up with :
This return first letter:
select substring(nazwisko,1,1) from t_autor where id_autora=26
select imie from t_autor where nazwisko like ???
how to connect this ? in a normal scenario it would be like '%letter%' but I'm going to get letter after subquery and I have no idea how to get it to work

Answer 1

You have the right idea with the subquery, and to getting the letter to use with LIKE can be accomplished with CONCAT: (as one possible way)
select substring(nazwisko,1,1) from t_autor where id_autora=26;
Gives:
Then using CONCAT as part of the subquery: (I added id_autora to show the reference)
select imie, id_autora from t_autor where nazwisko like (
select CONCAT(substring(nazwisko,1,1), '%') from t_autor where id_autora=26
);
-- The concat has a trailing % for names that start with the letter.
Gives:
As another example:
select substring(nazwisko,1,1) from t_autor where id_autora=20;
Gives:
Then used within the subquery:
select imie, id_autora from t_autor where nazwisko like (
select CONCAT(substring(nazwisko,1,1), '%') from t_autor where id_autora=20
);
Gives:
Here's a DB fiddle example. The query examples used above are at the bottom of the page. As Nick mentioned, having all the other tables was more than enough, so the fiddle only uses table t_autor.