MySQL 04 advanced query (II)

MySQL 04 Advanced query （ Two ）

One 、 Learning goals

1. master IN Usage of subquery
2. master EXISTS Subquery
3. Master the use principles and precautions of sub query
4. Able to use SQL Conduct comprehensive query

Two 、 Subquery replacement table connection

problem ：

• The query in “2020-01-02” I did it this day “ Urine routine ” List of patients for this examination

Use a variety of methods to realize query

Method 1 ： Use table connection

• perform prescription、patient and checkitem Three watches JOIN operation , Then screen the list of patients according to the conditions

Use JOIN Keyword implementation

SELECT patientName FROM patient pa 
INNER JOIN prescription pre ON pa.patientID = pre.patientID 
INNER JOIN checkitem c ON pre.checkItemID = c.checkItemID 
WHERE c.checkItemName = ' Urine routine ' AND pre.examDate = '2020-01-02';

Use WHERE Clause realization

SELECT patientName FROM patient pa,prescription pre, checkitem c
WHERE pa.patientID =  pre.patientID AND pre.checkItemID = c.checkItemID 
AND c.checkItemName = ' Urine routine ' AND pre.examDate = '2020-01-02';

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Mode two ： Use sub query to realize patient information screening of review conditions

Realize the idea :

1. Inquire about checkitem surface , get “ Urine routine ” Inspection item number of
2. According to the inspection item number , stay prescription The query in the table is “2020-01-02” The number of patients who had this examination on this day
3. According to the patient number in patient Look up the patient's name in the table

SELECT patientName FROM patient
WHERE patientID =
 (SELECT patientID FROM prescription
        WHERE checkItemID = 
            (SELECT checkItemID FROM checkitem
                 WHERE checkItemName = ' Urine routine ')  
AND examDate = '2020-01-02');

Summary and analysis ：

• Subquery is more flexible 、 convenient , It is often used as a screening condition for addition, deletion, modification and query , Suitable for manipulation A table of data
• Table connection change Suitable for see Multi table data

3、 ... and 、IN Subquery

problem ：

• If processing a subquery returns multiple records ？

analysis ：

• Use IN Subquery

grammar ：

• IN The syntax of the subquery

SELECT …… FROM  Table name  
WHERE  Field name   IN ( Subquery );

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3.1. Subquery returns multiple result examples ：

• The query in “2020-03-02” done “ blood fat 、 Blood glucose test ” List of patients for this examination

  SELECT patientName FROM patient WHERE patientID =
      (SELECT patientID FROM prescription WHERE checkItemID = 
          (SELECT checkItemID FROM checkitem 
                  WHERE checkItemName = ' blood fat 、 Blood glucose test ')
  AND examDate = '2020-03-02');
  

• Running results

  

• resolvent ： Use IN Subquery

3.2.IN Subquery example 1

• Commonly used IN Replace the equal sign operator （＝） Subquery of

• IN Subsequent subqueries can return multiple records

  #in: It limits the screening range of patient number , And subsequent sub queries can return multiple records 
  SELECT patientName FROM patient WHERE patientID IN
      (SELECT patientID FROM prescription WHERE checkItemID = 
          (SELECT checkItemID FROM checkitem 
           WHERE checkItemName = ' blood fat 、 Blood glucose test ')
  AND examDate = '2020-03-02');
  

  3.3.in Subquery example 2

problem ：

• The query was made in the last time “ blood fat 、 Blood glucose test ” Names of all patients who have seen the disease in the Department examined 、 Gender 、 Date of birth and address

Realize the idea ：

1. get “ blood fat 、 Blood glucose test ” The inspection item number of this inspection
2. Query the latest inspection date according to the obtained inspection item number
3. According to the obtained item number and the latest inspection date , Inquire the department number
4. Query the number of all patients who have seen diseases in these departments according to the department number
   • Be careful ： The department number obtained may be multiple records
5. Query the name of the patient according to the patient number 、 Gender 、 Date of birth and address

#1. get “ blood fat 、 Blood glucose test ” The inspection item number of this inspection 
SELECT checkItemID FROM checkitem WHERE checkItemName = ' blood fat 、 Blood glucose test ';

#2. Query the latest inspection date according to the obtained inspection item number 
SELECT MAX(examDate) FROM prescription WHERE checkItemID=(
SELECT checkItemID FROM checkitem WHERE checkItemName = ' blood fat 、 Blood glucose test ');

#3. According to the obtained item number and the latest inspection date , Inquire the department number 
SELECT depID FROM prescription 
WHERE examDate=(
SELECT MAX(examDate) FROM prescription WHERE checkItemID=(
 SELECT checkItemID FROM checkitem WHERE checkItemName = ' blood fat 、 Blood glucose test '))
  AND checkItemID = (
   SELECT checkItemID FROM checkitem WHERE checkItemName = ' blood fat 、 Blood glucose test ');

  #4. Query the number of all patients who have seen diseases in these departments according to the department number 
SELECT patientID FROM prescription 
WHERE depID IN (    
 SELECT depID FROM prescription 
   WHERE examDate = (
      SELECT MAX(examDate) FROM prescription 
      WHERE checkItemID = (
        SELECT checkItemID FROM checkitem 
        WHERE checkItemName = ' blood fat 、 Blood glucose test '  
       )  
    )
    AND checkItemID = (
      SELECT checkItemID FROM checkitem 
      WHERE checkItemName = ' blood fat 、 Blood glucose test '
    )
   )
   
#5. Query the name of the patient according to the patient number 、 Gender 、 Date of birth and address 
SELECT patientName, gender, birthDate, address FROM patient 
WHERE patientID IN (
SELECT patientID FROM prescription 
WHERE depID IN (    
   SELECT depID FROM prescription 
   WHERE examDate = (
      SELECT MAX(examDate) FROM prescription 
      WHERE checkItemID = (
        SELECT checkItemID FROM checkitem 
        WHERE checkItemName = ' blood fat 、 Blood glucose test '  
       )  
    )
    AND checkItemID = (
      SELECT checkItemID FROM checkitem 
      WHERE checkItemName = ' blood fat 、 Blood glucose test '
    )
   )
   );

Four 、NOT IN Subquery

problem ：

• The query was made in the last time “ blood fat 、 Blood glucose test ” Names of all patients who have seen the disease in other departments except the Department examined 、 Gender 、 Date of birth and address

  analysis ：

Realize the idea ：

1. get “ blood fat 、 Blood glucose test ” The inspection item number of this inspection
2. Query the latest inspection date according to the obtained inspection item number
3. According to the obtained item number and the latest inspection date , Inquire the department number
4. Query the number of all patients who have seen diseases in other departments except these departments according to the department number
5. Query the name of the patient according to the patient number 、 Gender 、 Date of birth and address

SELECT patientName, gender, birthDate, address FROM patient 
WHERE patientID IN (
#4. Query the number of patients who have seen diseases in other departments 
SELECT patientID FROM prescription WHERE depID NOT IN (
   #3. Inquire the department number 
   SELECT depID FROM prescription WHERE examDate=(
      #2. Query the latest inspection date according to the inspection item number 
      SELECT MAX(examDate) FROM prescription 
      WHERE checkItemID=(
        #1. get “ blood fat 、 Blood glucose test ” Check item number 
        SELECT checkItemID FROM checkitem 
        WHERE checkItemName = ' blood fat 、 Blood glucose test ' 
      )
    )
    AND checkItemID = (
      #1. get “ blood fat 、 Blood glucose test ” Check item number 
      SELECT checkItemID FROM checkitem 
      WHERE checkItemName = ' blood fat 、 Blood glucose test ' 
    )
   )
   );
  

5、 ... and 、EXISTS Subquery

problem ：

• How to use SQL Statement detection log Whether the table has been created ？

  DROP TABLE IF EXISTS log;
  CREATE TABLE IF NOT EXISTS log (
      … … # Omit the table creation statement 
  );
  

• EXISTS Whether there are other uses of keywords ？

  • EXISTS Subquery

grammar ：

SELECT …… FROM  Table name  WHERE  EXISTS ( Subquery );

• Subqueries have returned results ： EXISTS The subquery result is TRUE
• The subquery returns no results ： EXISTS The subquery result is FALSE, The outer query does not execute

Example ：

demand ：

• Find out if any patients have done “ blood fat 、 Blood glucose test ”
  • If there is , Please display the name of the patient who has undergone this examination 、 Gender 、 Age 、 Inspection date and results

analysis ：

• Use EXISTS Subquery to find out whether any patients have done “ blood fat 、 Blood glucose test ”
  • If a patient has done “ blood fat 、 Blood glucose test ”, from patient Table and prescription Query the name of the patient who has done this examination in the table 、 Gender 、 Age 、 Inspection date and results
  • Use EXISTS Subquery can detect whether there are records that meet the query criteria. If there are , Then query the corresponding records that meet the requirements according to the business logic

# Query patient information and examination information , The patient's age is calculated according to the date of birth 
SELECT 
	patientName,
	gender,
	FLOOR(DATEDIFF(CURDATE(),birthDate)/365) AS age 
FROM patient
# Use EXISTS Clause to determine whether it has been done “ blood fat 、 Blood glucose test ” Patients 
WHERE EXISTS(
 SELECT patientID FROM prescription 
 WHERE checkItemID = (
		SELECT checkItemID FROM checkitem 
		WHERE checkItemName=' blood fat 、 Blood glucose test ') 
 AND patient.patientID = prescription.patientID);

• and IN Like subqueries ,EXISTS Subqueries can also be added NOT Keyword implements the opposite operation
  • NOT EXISTS It means that there is no record in the result set and it returns true, Otherwise return to false！

6、 ... and 、NOT EXISTS Subquery

problem ：

• Inquire patients “ Li Siyu ” Have you ever done it “ Coagulation five ” Check
  • If I haven't done it , Then insert a record
    • With “ internal medicine ” In the name of today, give her a “ Coagulation five ” The inspection of

analysis ：

• You can use NOT EXISTS Subquery detection “ Li Siyu ” Have you ever done it “ Coagulation five ” Check
  • If NOT EXIST The execution result of the subquery returns true, Then perform data insertion

INSERT INTO prescription(patientID,depID,examDate,checkItemID)
SELECT patientID, 3 as depID, CURDATE() as examDate, 4 as checkItemID 
FROM patient 
WHERE NOT EXISTS (SELECT patientID FROM prescription 
                   WHERE checkItemID = (
	            SELECT checkItemID FROM checkitem 
		     WHERE checkItemName=' Coagulation five ') 
	    AND patient.patientID = prescription.patientID) 
AND patientName=' Li Siyu ';

7、 ... and 、 Sub query summary

• What is subquery ？
  • When one query is a condition of another , It's called a subquery
• Subqueries can appear in SQL Where is the statement ？
  • Subqueries can be used wherever expressions are allowed
  • Nested in parent query SELECT Subquery of statement , May include
    1. SELECT Clause
    2. FROM Clause
    3. WHERE Clause
    4. GROUP BY Clause
    5. HAVING Clause

8、 ... and 、 Sub query considerations

• Usually , Place subqueries to the right of the comparison criteria to increase readability
• Subqueries can return single or multiple rows of data , At this point, choose the appropriate keyword
  • When the sub query returns single row data , Comparison operators can be used in comparison conditions
  • When the sub query returns multiple rows of data , You need to use IN or NOT IN keyword
  • If you decide whether there is data returned from the sub query , Need to use EXISTS or NOT EXISTS keyword
• Only appear in subqueries 、 Columns that do not appear in the parent query cannot be included in the output column

Nine 、 Summary of this chapter