Data integrity
1. What is data integrity
Ensure the preservation of user-entered data into the database is correct.
2. How to add data integrity
Add a constraint to the table when you create a table
3. Integrity Category
Entity integrity, domain integrity, referential integrity
Entity integrity
1. What is the entity integrity
Table row (record) on behalf of an entity (Entity)
2. The role of entity integrity
Identify each row of data is not repeated. Row-level constraints
3. constraint type
Primary key constraint (primary key)
The only constraint (unique)
Automatic growth column (auto_increment)
The primary key constraint
Features: each table have a primary key. The only data, and not be null
Adding way
CREATE TABLE table name (field data type 1 primary key, the field data type 2);
CREATE TABLE table name (data type of the field 1, field 2 data type, primary key (primary key fields to be set));
CREATE TABLE table name (data type of the field 1, field 2 data type, primary key (primary key of the primary key 2));
Primary key
Two fields with the same data at the same time, only the primary key constraint violation.
1. create table
2. go to modify the table, add a primary key
ALTER TABLE student ADD CONSTRAINT PRIMARY KEY (id);
The only constraint
Features: data specified column can not be repeated, can be null
format
CREATE TABLE table name (1 Field Name Field Data Type Data Type UNIQUE 2);
Automatic growth column
Features: automatic data specified column growth, even if the data is deleted, or continue down the serial number removed
format
CREATE TABLE table name (1 Field Name Data Type PRIMARY KEY AUTO_INCREMENT, the data type field UNIQUE 2);
Domain integrity
use
Limit this cell data is correct, the comparison of other cells in the column as such does not
Domain represents the current cell
Domain integrity constraints
Data type: numeric type, date type, string type
Non-empty constraint (not null)
CREATE TABLE table name (1 Field Name Data Type PRIMARY KEY AUTO_INCREMENT, the second data type field UNIQUE not null);
The default value constraints (default)
CREATE TABLE table name (1 Field Name Data Type PRIMARY KEY AUTO_INCREMENT, the second data type field UNIQUE not null default 'M');
When inserted, the value of which is directly to the default values
Referential integrity
1. What is referential integrity
It refers to a correspondence between the table and the table
Normally provided by the primary bond between the two tables, the foreign key relationship, two or write trigger table to achieve.
There are two tables correspond to reference the integrity of their data in the process of insert, update, delete, the system will be modified to correspond to the table and another table were compared, thereby preventing operation of some incorrect data.
2. Note
Primary keys and foreign keys in the database must be consistent with the type;
If the two tables have to type InnoDB
After setting the referential integrity, the contents of which the foreign key, the contents have to be among the primary key
Field as the primary key of a table is provided which, provided the primary key table based
CREATE TABLE student(sid int PRIMARY key,name varchar(50) not null,sex varchar(10) default '男');
When you create a table, foreign key, foreign key of the child table
CREATE TABLE score( sid INT, score DOUBLE, CONSTRAINT fk_stu_score_sid FOREIGN KEY(sid) REFERENCES student(sid) );
Relationships between tables
One: monogamy
Many relationship: A person can have many cars, all requests for access to a vehicle owned by individuals.
-- Person表 CREATE TABLE person( id int primary key NOT NULL, name VARCHAR(50)， age int, sex CHAR(1) );
-- Car表 CREATE TABLE car( cid int primary key, cname varchar(50), color varchar(25), pid int, CONSTRAINT fk_Person FOREIGN KEY(pid) REFERENCES person(id) );
Many relationship:
Student enrollment, a student may have many courses, each course for more students to choose.
A student can have multiple teacher, and a teacher can have more than one student
1. Create table teacher
CREATE TABLE teacher( tid INT PRIMARY KEY auto_increment, name VARCHAR(50), age int, gender char(1) DEFAULT '男' );
2. Create a table of students
CREATE TABLE student( sid int PRIMARY KEY auto_increment, name VARCHAR(50) NOT NULL, age int, gender CHAR(1) DEFAULT '男' );
3. Create a table of students and teachers
CREATE TABLE tea_stu_rel( tid INT, sid INT );
4. Add Foreign Key
ALTER TABLE tea_stu_rel ADD CONSTRAINT fk_tid FOREIGN KEY(tid) PEFERENCES teacher(tid); ALTER TABLE tea_stu_rel ADD CONSTRAINT fk_sid FOREIGN KEY(sid) PEFERENCES student(id);
Why split the table? Avoid large numbers of redundant data
Multi-table query
The combined result set
1. What is the combined result set
The combined result set is to query the results of two select statements merged together
2. merge two ways the result set
Merging repeated removal recording UNION
UNION ALL is not removed when the combined duplicate records
format:
SELECT * FROM 表1 UNION SELECT * FROM 表2；
SELECT * FROM 表1 UNION ALL SELECT * FROM 表2;
Examples
1. Create a table
CREATE TABLE A(name varchar(10),score int); CREATE TABLE B(name varchar(10),score int); INSERT INTO A VALUES('a',10),('b',20),('c',30); INSERT INTO B VALUES('a',10),('b',20).('d',40);
2.UNIONSELECT * FROM A UNION SELECT * FROM B;
3.UNION ALLSELECT * FROM A UNION ALL SELECT * FROM B;
Precautions
The combined results of the two: the number of columns, the column must be the same type.
Join query
1. What is the connection query
Queries can also be called across the table, you need to associate multiple tables query
2. What is the Cartesian set
Hypothesis set A = {a, b}, set B = {0,1,2},
Cartesian product of the two sets of {(a, 0), (a, 1), (a, 2), (b, 0), (b, 1), (b, 2)}.
It can be extended to a plurality of sets of
Meanwhile queries two tables, there is the Cartesian set of results
Since the alias to the table when the query
SELECT * FROM student stu,score sc;
3. multi-table joint investigation, how to ensure data is correct
When the query should the primary and foreign keys consistent SELECT * FROM stu st, score sc WHERE st.id = sc.sid;
Primary table data among the reference data among the sub-table
principle
Progressive judgment, leaving an equal, not equal whole do not
Classified according to the connection
En
First, the equivalent connection
id number (value) of only two simultaneous display table
SELECT * FROM stu st INNER JOIN score sc ON st.id = sc.sid;
Table check constraints associated with multiple primary foreign key is the same, but changing the wording.
Write-back of only the main foreign key ON
If there are conditions where write directly behind
SELECT st.name,sc.score,sc.km FROM stu st INNER JOIN score sc ON st.id = sc.sid WHERE score>=70;
Multi-table joint investigation and there are conditions to write and direct
Second, multi-table joins
The establishment of student scores, chart
99 using the joining method
SELECT st.name,c.name,sc.score FROM stu st,score sc,course c WHERE st.id = sc.sid AND sc.cid = c.cid;
Use inline query
SELECT st.name,c.name,sc.name FROM stu st INNER JOIN score sc ON st.id = sc.sid INNER JOIN course c ON sc.cid = c.cid;
Third, non-equivalent connection
Example Table
Query the names of all employees, wages, the name of the department and the level of wages
1. Query the names of all employees, wages
SELECT ename,salary FROM emp;
2. Query the names of all employees, wages and all sectors - SELECT e.ename, e.salary, d.dname FROM emp e, dept d WHERE e.deptno = d.deptno; SELECT e.name, e.salaru, d.dname FROM emp e JOIN dept d ON e.deptno = d.deptno;
3. Query the names of all employees, wages and wage levels and where the department
SELECT e.ename,e.salary,d.dname,g.grade FROM emp e JOIN dept d ON e.deptno = d.deptno JOIN salgrade g ON e.salary BETWEEN g.lowSalary AND g.highSalary;
Fourth, external connection
1. The left outer connector (left connector)
Meet the conditions of the same two data tables check out, if there is not the same among the left of the data table, the data table on the left is also among the check out.
Among all the data table on the left found the right watch them, just find out the condition of contents
When using the connector, seven weeks does not check out, no score, the absent. All the test over the test scores of students to check out.
SELECT st.name,sc.score,sc.km FROM stu st,score sc WHERE st.id = sc.sid
SELECT st.name,sc.score,sc.km FROM stu st INNER JOIN score sc ON st.id = sc.sid;
Use the left join query for all students and student test scores
SELECT st.name,sc.score,sc.km FROM stu st LEFT OUTER JOIN score sc ON st.id = sc.sid;
All data is left connected to the left table will among identified, of which only found the right table to meet the conditions of data
You can not write omitted outer
Query, two tables may not be required to establish the primary foreign key constraint
2. The right outer connector (right connection)
All data among the right connection will find out the right, the left table only find out which satisfy the conditions of data
SELECT st.name,sc.score,sc.km FROM stu st RIGHT JOIN score sc ON st.id = sc.sid;
All in all the right data tables found among the left table only find out the condition of the recording
Standing on the perspective to see the table, use the left left put the connection table of contents among all found the right found to meet the criteria.
Using the right connection, put the data table on the right among all find out. The left found to meet the conditions.
Fifth, the natural connection
Join query produces unwanted Cartesian set, we usually use the primary foreign key relationship equation to remove it.
The natural connection without you having to give the primary foreign key equation, it will automatically find this equation
That do not have to write condition
Claim
Two table names and column connection type of column as the identical conditions
Removes the same column
SELECT * FROM stu NATURAL JOIN score;
Subqueries
1. What is a subquery
A select statement contains another complete select statement.
Or two or more SELECT, then that is a sub-query.
2. The position of the sub-queries appear
After the where, the select query results as a condition of the value of another select
After the from, to check out the new results as a table;
Example Table
use
Xiang Yu query with the same department staff person
1. First, find out where the department number Xiang Yu
SELECT deptno FROM emp WHERE ename = '项羽';
2. According to again check the number of employees in the same department
SELECT ename,depatno FROM emp WHERE depatno = (SELECT deptno FROM emp WHERE ename = '项羽');
Article 1 the result of check out when the condition statement Day 2
Queries wages higher than Yaojin employees
1. identify Yaojin wages
SELECT salary FROM emp WHERE ename = 'Yaojin';
2. go check out the name of the employee record is greater than the value of the results ISOLATED
SELECT ename,salary FROM emp WHERE salary > (SELECT salary FROM emp WHERE ename='程咬金');
Paid more than 30 department employee information for all
1. First, find out the 30th highest paid man department
SELECT MAX(salary) FROM emp WHERE deptno = 30;
2. then query the entire table is greater than 30, the highest wage sectors of the man
SELECT ename,salary FROM emp WHERE salary > (SELECT MAX(salary) FROM emp WHERE deptno = 30);
Queries jobs and wages and Daji same employee information
1. Da has been working to identify and wages
SELECT job,salary FROM emp WHERE ename='妲己';
The query results as a condition to go to work and the same wages
SELECT ename,job,salary FROM emp WHERE (job,salary) IN (SELECT job,salary FROM emp WHERE enname='妲己');
Since the two conditions, the determination using the IN
There are more than two employee information direct reports
1. group all the superior numbers
SELECT mgr,GROUP_CONCAT(mgr) FROM emp GROUP BY mgr;
2. Identify greater than 2 and greater than 2 illustrates two subordinates
SELECT mgr,GROUP_CONCAT(mgr) FROM emp GROUP BY mgr HAVING COUNT(*) >= 2;
3. When the row of the query results as employee number on the bar
SELECT ename FROM emp WHERE empno IN (SELECT mgr FROM emp GROUP BY mgr HAVING COUNT(*) >= 2)
Queries employee number for employees to name 7788, staff salaries, department name, department address
SELECT e.name,e.salary,d.dname,d.local FROM emp e,dept d WHERE e.deptno = d.deptno AND empno = 7788;
Since the connection
7369 seeking employee number, name, number, and manager Managers Name
SELECT * FROM emp WHERE empno = (SELECT mgr FROM emp WHERE empno=7369);
Above this method can only check out the name of a manager
Since the connection: connect your own, surnamed
SELECT * FROM emp e1,emp e2 WHERE e1.mgr = e2.empno AND e1.empno = 7369;
Old nine school community members produced