SQL luyện code - JinMing Lab

dinh nghia truoc

SQL la gi

SQL dung de viet chi dan chinh xac. O day ban hoc theo lo trinh thuc hanh de hoc SQL tu con so 0. Hay bat dau voi mot mo hinh: dau vao qua cac buoc roi thanh dau ra.

thong tin chay toi thieutep query.sqlchay psql -f query.sqlthoi quen hoc mot phan nho cua SQL, go vi du toi thieu roi chay

chuong trinh

tap hop lenh duoc chay theo thu tu.

gia tri va bien

gia tri la du lieu. bien la ten de giu du lieu.

ham

mot viec nho co ten, nhan dau vao va tao ket qua.

moi truong

PostgreSQL compatible SQL chay code trong query.sql.

doan code dau tien

Select

columns table rows

SELECT name, score FROM users;

dau ra name score rows

pha he ngon ngu

cay pha he SQL

xem SQL den tu dau, gan voi ngon ngu nao, va nen hoc gi tiep.

goc

relational algebraSEQUEL

hien taiSQLho du lieu va tinh toan khoa hoc

gan nhau

R Python Julia MATLAB

ho ngon nguho du lieu va tinh toan khoa hoc

phu hop cho

phu hop cho lo trinh thuc hanh de hoc SQL tu con so 0

hoc tiep

Python Go Bash

tu con so 0

1doc mot quy tac2doan dau ra3go bang tri nho4chay kiem tra5lap lai voi mot thay doi

Ngan hang cau hoi

Tim truoc khi luyen

Chon giai doan hoac tim trong ngan hang cua ngon ngu nay roi mo bai tap.

18 ket qua

Tim cau hoi lap trinh

Q 1Lua chonGiai doan 1 dinh nghia

SQL cau 1

SQL cau 1. Chon mo ta phu hop nhat voi select columns.

Q 2Lua chonGiai doan 1 dinh nghia

SQL cau 2

SQL cau 2. Chon mo ta phu hop nhat voi where filter.

Q 3Lua chonGiai doan 1 dinh nghia

SQL cau 3

SQL cau 3. Chon mo ta phu hop nhat voi count aggregate.

Q 4Lua chonGiai doan 1 dinh nghia

SQL cau 4

SQL cau 4. Chon mo ta phu hop nhat voi join tables.

Q 5Lua chonGiai doan 1 dinh nghia

SQL cau 5

SQL cau 5. Chon mo ta phu hop nhat voi select columns.

Q 6Lua chonGiai doan 1 dinh nghia

SQL cau 6

SQL cau 6. Chon mo ta phu hop nhat voi where filter.

Q 7Lua chonGiai doan 1 dinh nghia

SQL cau 7

SQL cau 7. Chon mo ta phu hop nhat voi count aggregate.

Q 8Lua chonGiai doan 1 dinh nghia

SQL cau 8

SQL cau 8. Chon mo ta phu hop nhat voi join tables.

Q 9Lua chonGiai doan 1 dinh nghia

SQL cau 9

SQL cau 9. Chon mo ta phu hop nhat voi select columns.

Q 10Lua chonGiai doan 1 dinh nghia

SQL cau 10

SQL cau 10. Chon mo ta phu hop nhat voi where filter.

Q 11Lua chonGiai doan 1 dinh nghia

SQL cau 11

SQL cau 11. Chon mo ta phu hop nhat voi count aggregate.

Q 12Lua chonGiai doan 1 dinh nghia

SQL cau 12

SQL cau 12. Chon mo ta phu hop nhat voi join tables.

Q 13Lua chonGiai doan 1 dinh nghia

SQL cau 13

SQL cau 13. Chon mo ta phu hop nhat voi select columns.

Q 14Lua chonGiai doan 1 dinh nghia

SQL cau 14

SQL cau 14. Chon mo ta phu hop nhat voi where filter.

Q 15Lua chonGiai doan 1 dinh nghia

SQL cau 15

SQL cau 15. Chon mo ta phu hop nhat voi count aggregate.

Q 16Lua chonGiai doan 1 dinh nghia

SQL cau 16

SQL cau 16. Chon mo ta phu hop nhat voi join tables.

Q 17Lua chonGiai doan 1 dinh nghia

SQL cau 17

SQL cau 17. Chon mo ta phu hop nhat voi select columns.

Q 18Lua chonGiai doan 1 dinh nghia

SQL cau 18

SQL cau 18. Chon mo ta phu hop nhat voi where filter.

trac nghiem

SQL cau 1

Q 1Lua chonmoi

cau

SQL cau 1. Chon mo ta phu hop nhat voi select columns.

SELECT name FROM users;

tham khao

mau cho query.sql

PostgreSQL compatible SQLpsql -f query.sql

nho laidoc mot y nho roi viet lai ma khong nhin

lan theo codeghi gia tri bien tung dong truoc khi chay

tu goit copy hon go nhieu hon va sua mot loi nho

columns table rows

Select

SELECT name, score FROM users;

Select only needed columns
Read from one table first
Add limits while exploring

where order limit

Filter

SELECT name FROM users WHERE score >= 60;

WHERE filters rows
ORDER BY sorts
LIMIT protects exploration

count sum avg group by

Group

SELECT role, COUNT(*) FROM users GROUP BY role;

Aggregate after filtering
Group by non aggregate columns
Name metrics clearly