PostgreSQL - 选择查询

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  简述

  PostgreSQLSELECT语句用于从数据库表中获取数据，以结果表的形式返回数据。这些结果表称为结果集。
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  句法

  SELECT 语句的基本语法如下 -

  
  SELECT column1, column2, columnN FROM table_name;
  

  这里，column1,column2...是表的字段，您要获取其值。如果要获取字段中所有可用字段，则可以使用以下语法 -

  
  SELECT * FROM table_name;
  

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  例子

  考虑具有以下记录的表 COMPANY -

  
  -- This is the file to create COMPANY table and to populate it with 7 records.
  -- Just copy and past them on psql prompt.
  DROP TABLE COMPANY;
  CREATE TABLE COMPANY(
     ID INT PRIMARY KEY     NOT NULL,
     NAME           TEXT    NOT NULL,
     AGE            INT     NOT NULL,
     ADDRESS        CHAR(50),
     SALARY         REAL
  );
  INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
  VALUES (1, 'Paul', 32, 'California', 20000.00 );
  
  INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
  VALUES (2, 'Allen', 25, 'Texas', 15000.00 );
  
  INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
  VALUES (3, 'Teddy', 23, 'Norway', 20000.00 );
  
  INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
  VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 );
  
  INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
  VALUES (5, 'David', 27, 'Texas', 85000.00 );
  
  INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
  VALUES (6, 'Kim', 22, 'South-Hall', 45000.00 );
  
  INSERT INTO COMPANY VALUES (7, 'James', 24, 'Houston', 10000.00 );
  

  
   id | name  | age | address   | salary
  ----+-------+-----+-----------+--------
    1 | Paul  |  32 | California|  20000
    2 | Allen |  25 | Texas     |  15000
    3 | Teddy |  23 | Norway    |  20000
    4 | Mark  |  25 | Rich-Mond |  65000
    5 | David |  27 | Texas     |  85000
    6 | Kim   |  22 | South-Hall|  45000
    7 | James |  24 | Houston   |  10000
  (7 rows)
  

  以下是一个示例，它将获取 CUSTOMERS 表中可用客户的 ID、Name 和 Salary 字段 -

  
  testdb=# SELECT ID, NAME, SALARY FROM COMPANY ;
  

  这将产生以下结果 -

  
    id | name  | salary
   ----+-------+--------
     1 | Paul  |  20000
     2 | Allen |  15000
     3 | Teddy |  20000
     4 | Mark  |  65000
     5 | David |  85000
     6 | Kim   |  45000
     7 | James |  10000
  (7 rows)
  

  如果要获取 CUSTOMERS 表的所有字段，请使用以下查询 -

  
  testdb=# SELECT * FROM COMPANY;
  

  这将产生以下结果 -

  
   id | name  | age | address   | salary
  ----+-------+-----+-----------+--------
    1 | Paul  |  32 | California|  20000
    2 | Allen |  25 | Texas     |  15000
    3 | Teddy |  23 | Norway    |  20000
    4 | Mark  |  25 | Rich-Mond |  65000
    5 | David |  27 | Texas     |  85000
    6 | Kim   |  22 | South-Hall|  45000
    7 | James |  24 | Houston   |  10000
  (7 rows)