JavaEE基础知识学习----PostgreSQL数据库（二）查询工具

PostgreSQL查询工具

INSERT语句

INSERT INTO EMPLOYEES(  ID, NAME, AGE, ADDRESS, SALARY)  
VALUES
 (1, 'Maxsu', 25, '海口市人民大道2880号', 109990.00 ), 
(2, 'minsu', 25, '广州中山大道 ', 125000.00 ), 
(3, '李洋', 21, '北京市朝阳区', 185000.00),   
(4, 'Manisha', 24, 'Mumbai', 65000.00), 
(5, 'Larry', 21, 'Paris', 85000.00);

SELECT语句

SELECT ID, NAME, AGE, SALARY  FROM EMPLOYEES;

UPDATE语句

UPDATE table_name  
SET column1 = value1, column2 = value2...., columnN = valueN  
WHERE [condition];

DELETE语句

DELETE FROM table_name  
WHERE [condition];

注意：如果不使用“WHERE”条件，整个表中的记录都将被删除

ORDER BY语句

ORDER BY子句用于按升序或降序对数据进行排序。数据在一列或多列的基础上进行排序。

SELECT column-list  
FROM table_name  
[WHERE condition]  
[ORDER BY column1, column2, .. columnN] [ASC | DESC];

GROUP BY语句

GROUP BY子句用于将具有相同数据的表中的这些行分组在一起。 它与SELECT语句一起使用。GROUP BY子句通过多个记录收集数据，并将结果分组到一个或多个列。 它也用于减少输出中的冗余

SELECT column-list  
FROM table_name  
WHERE [conditions ]  
GROUP BY column1, column2....columnN  
ORDER BY column1, column2....columnN

实例,按name分组，统计薪水

SELECT NAME, SUM(SALARY)   
FROM EMPLOYEES   
GROUP BY NAME;

HAVING IN语句

HAVING子句与GROUP BY子句组合使用，用于选择函数结果满足某些条件的特定行。

SELECT column1, column2  
FROM table1, table2  
WHERE [ conditions ]  
GROUP BY column1, column2  
HAVING [ conditions ]  
ORDER BY column1, column2

实例，查询表中名字相同数大于2

SELECT NAME,COUNT (NAME) 
FROM EMPLOYEES  
GROUP BY NAME HAVING COUNT (NAME) > 2;