PgSQL learning notes

PgSQL course

1. value type
   

2. Create database

-- Create a  runoobdb  The database of ：
create database runoobdb;

5. Delete database

--  Delete database 
DROP DATABASE xyx;

7. Create a table

--  Create a table 
CREATE TABLE table_01(
id INT PRIMARY KEY NOT NULL,
name VARCHAR(50),
age INT
);

9. Delete table

--  Delete table 
DROP TABLE table_01;

11. PostgreSQL Pattern （SCHEMA）

--  Create mode 
CREATE SCHEMA test01
--  Delete the pattern 
DROP SCHEMA test01

13. INSERT INTO （ Insert ）

--  Insert table-01 surface   Insert only id,name
INSERT INTO table_01 ( ID, NAME )
VALUES
	( 15, ' Li Si ' );

--  Insert all 
INSERT INTO table_01
VALUES
	( 45, ' Zhang San ', 25 );

Return result description ：

INSERT oid 1

 Insert only one row and the target table has  OID The return information of ,  that  oid  Is assigned to the inserted row  OID.

INSERT 0 #

 Insert multiple rows of returned information , #  Is the number of rows inserted .

The following insert statement JOIN_DATE Fields use DEFAULT Clause to set the default value , Instead of specifying a value ：

--  The following insert statement  JOIN_DATE  Fields use  DEFAULT  Clause to set the default value , Instead of specifying a value ：
INSERT INTO table_01	(	ID,	NAME ,age ,JOIN_DATE )
VALUES
	(78,' Aton ',28,DEFAULT);

15. SELECT（ Inquire about ）

--  Inquire about 
SELECT * FROM table_01;

16. Operator
    
    A simple example ：

SELECT 2+3;
SELECT 2*3;
SELECT 10/5;
SELECT 2-3;
--  Remainder 
SELECT 12%5;
--  Index 
SELECT 2^3;
--  square root 
SELECT |/ 25.0;
--  Cube root 
SELECT ||/ 27.0;

18. expression
    

--  Read  SALARY  Field is greater than the  50000  The data of 
SELECT * FROM COMPANY WHERE salary>5000;
--  Read  SALARY  Field equals  20000  The data of 
SELECT * FROM COMPANY WHERE salary=20000;
--  Read  SALARY  The field is not equal to  20000  The data of 
SELECT * FROM COMPANY WHERE salary>65000;
--  Read  SALARY  Field is greater than or equal to  65000  The data of 
SELECT * FROM COMPANY WHERE salary>=65000;

Logical operators

PostgreSQL  There are several logical operators ：

SQL Use a three valued logic system , Include true、false and null,null Express " Unknown ".

--  Read  AGE  Field is greater than or equal to  25  And  SALARY  Field is greater than or equal to  6500  The data of ：
SELECT * FROM company WHERE age>=25 and salary>=6500;
--  Read  AGE  Field is greater than or equal to  25  or  SALARY  Field is greater than the  6500  The data of ：
SELECT * FROM company WHERE age >=25 or salary>6500; 
--  Read  SALARY  Field is not  NULL  The data of ：
SELECT * FROM company WHERE salary is NOT NULL;

19. WHERE Clause

A Boolean expression reads data according to a specified condition ：

SELECT * FROM COMPANY WHERE salary=20000;

Numeric expressions are often used in mathematical operations in query statements ：

SELECT (17 + 6) AS ADDITION ;

Besides PostgreSQL There are also built-in mathematical functions , Such as ：

avg() ： Returns the average value of an expression
sum() ： Returns the sum of the specified fields
count() ： Returns the total number of records queried

--  Total number of records queried 
SELECT COUNT(*) AS "RECORDS" FROM COMPANY;

--  Query the current time  current_timestamp
SELECT CURRENT_TIMESTAMP;

21. AND & OR Operator

WHERE Clause using a comparison operator or a logical operator , for example >, <, =, LIKE, NOT wait

IN following SELECT Statement lists AGE( Age ) Field is 25 or 27 The data of ：

SELECT * FROM COMPANY WHERE AGE IN ( 25, 27 );

NOT IN
following SELECT Statement lists AGE( Age ) Field is not 25 or 27 The data of ：

SELECT * FROM COMPANY WHERE AGE NOT IN ( 25, 27 );

BETWEEN
following SELECT Statement lists AGE( Age ) Field in 25 To 27 The data of ：

SELECT * FROM COMPANY WHERE AGE BETWEEN 25 AND 27;

Subquery
Following SELECT The sentence uses SQL Subquery of , Read... In subquery statement SALARY( Salary ) Field is greater than the 65000 The data of , And then through EXISTS Operator to determine whether it returns a line , If there is a return line, read all AGE( Age ) Field .

SELECT age FROM company WHERE EXISTS (SELECT age from
company WHERE salary >6500);

Read... In subquery statement SALARY( Salary ) Field is greater than the 65000 Of AGE( Age ) Field data , And then use > The operator query is greater than this AGE( Age ) Field data ：

--  Read... In subquery statement  SALARY( Salary )  Field is greater than the  65000  Of  AGE( Age )  Field data , And then use  >  The operator query is greater than this  AGE( Age )  Field data 
SELECT * FROM company WHERE age>(SELECT age FROM company WHERE salary>65000);

22. UPDATE sentence

to update COMPANY In the table id by 3 Of salary field value ：

UPDATE company SET 	salary = '90000' WHERE id=3;

Simultaneous updating salary Fields and address Value of field ：

--  Simultaneous updating  salary  Fields and  address  Value of field 
UPDATE company SET salary = '10000',address=' Beijing China ' WHERE id=3;

Delete delete

--  Delete id=8 The data of 
DELETE FROM company WHERE id=8;

23. LIKE Clause

-- find  SALARY  In the field, use  200  Initial data .
WHERE SALARY::text LIKE '200%' 
--------------------------------------------------------------------------------------------------------------
-- find  SALARY  The field contains  200  Character data .
WHERE SALARY::text LIKE '%200%'
--------------------------------------------------------------------------------------------------------------
-- find  SALARY  There are... In the second and third positions in the field  00  The data of 
WHERE SALARY::text LIKE '_00%'
--------------------------------------------------------------------------------------------------------------
-- find  SALARY  In the field, use  2  The length of the first character is greater than  3  The data of .
WHERE SALARY::text LIKE '2_%_%'
--------------------------------------------------------------------------------------------------------------
-- find  SALARY  In the field, use  2  Data at the end 
WHERE SALARY::text LIKE '%2'
--------------------------------------------------------------------------------------------------------------
-- find  SALARY  Field  2  In the second position and with  3  Data at the end 
WHERE SALARY::text LIKE '_2%3'
--------------------------------------------------------------------------------------------------------------
--  find  SALARY  In the field, use  2  start ,3  It ends with  5  Digit data 
WHERE SALARY::text LIKE '2___3'
--------------------------------------------------------------------------------------------------------------

example , Extract... From the third place 3 A record

SELECT * FROM COMPANY LIMIT 3 OFFSET 2;