Yesterday Content:
a variant (*************) foreign key.
Unique index
unique ( 'name'): This column is not repeated
joint unique index:
UNIQUE ( 'name', ' age '): in these two columns can not be repeated
many
Department:
ID depart_name
. 1 PR
2 xxx portion
User:
ID username depart_id (foreign key constraints)
. 1. 1 the root
2 root2 2
. 3. 1 root3
one
to see traffic demand
User:
ID username depart_id (foreign key constraint)
. 1. 1 the root
2 root2 2
. 3. 1 root3
Blog:
ID user_id URL (unique foreign key constraints +)
. 1 / the root /. 1
2 / root3 /. 3
-many
User:
ID username
the root. 1
2 root2
. 3 root3
Host:
hostname ID
. 1 c1.com
2 c2.com
. 3 c3.com
user2host:
ID HID UID (unique joint foreign key +)
. 1. 1. 1
2. 1 2
. 3. 3. 1
. 4. 3. 3
two detailed operation of the data line.
by:
INSERT INTO T1 (name, Age) values ( 'LXXX', 12 is);
INSERT INTO T1 (name, Age) values ( 'LXXX', 12 is), ( 'XXXXX', 13 is), ( 'xxxxxx', 13 is);
INSERT INTO T1 (name, age) select name, age from t2;
deletion:
Delete from T1;
Delete from T1 WHERE name = 'XXX' and Age = 12 is;!
update:
update T1 SET name = 'XXX', Age = 123 WHERE name = 'xxxx' and age = 13;
query:
wildcard:
like name 'Li'
%: match all
_: matches one character
limit access to data:
limit from the start to take the first few (index) strip, the number of pieces of data to
Page: (***********)
Page = 1,2,3,4,5 ... n-
offset = 10
limit (-Page. 1) * offset, offset;
sort:
Order by column name ASC (ascending), desc (descending)
packet:
the data are grouped by a column
group by + aggregate functions (COUNT / SUM () / AVG () / max () / min ())
HAVING
connected table:
left the Join:
left the entire show
right join:
all right of the
left join
Today contents:
A job
navcate formysql
1, the query is more than 60 points all students name and student number
ideas:
that a few tables:
associate two tables: Student Score
the SELECT * from Score score.student_id = ON left the Join Student Student. sid;
query never learned "Ping" the teacher's class of students number, name
inquiry learned "Li Ping" the students of the teacher's lesson number, name
"Ping teacher" taught courses ID
query
has at least one course with students learn the same curriculum number and name student number "1," the students have learned
1 2, 4
the SELECT COURSE_ID from the WHERE student_id Score = 1; ##, 2, 4
the SELECT student_id Score from COURSE_ID in the WHERE (COURSE_ID from the SELECT WHERE the student_id. 1 = Score)
SELECT SID, SID in sname from Student WHERE (SELECT from the student_id Score COURSE_ID in WHERE (SELECT = COURSE_ID Score. 1 from the student_id WHERE) HAVING SID! =. 1)
select student.sid, student.sname from student left join score on student.sid = score.student_id where sid!=1 and course_id in (select course_id from score where student_id=1)
tee : 重定向导入某一个文件
Two pymysql (Python operations MySQL).
PIP3 install pymysql
Note:
. A conn, the Cursor run out need to close the resource connection
b query time, fetchone, fetchmany, fetchall, default returns a tuple, need to return to dictionary words:. Cursor = conn.cursor (the Cursor = pymysql.cursors.DictCursor)
c. deletion and update when we needed after execute, add conn.commit ()