slq clause

一、查询：
SELECT被用来检索从一个或多个表中精选的行。select_expression指出你想要检索的列。SELECT也可以用

来检索不引用任何表的计算行
1、select*from table1;
2、select field1,field2 from table1;
3、select count(*)from table2;
4、select table1.filed1,table2.filed2 from table1,table2 where table1.field1='valed1';
5、select *from table1 where field1='valed1' and fiels2='valed2' orded by field1;
6、select*from table1 where filed1='valed1' order byfiled1 desc linit n;
7、select *from table2 where name like '%$lin%';(模糊)
8、sub_selects(高级)
select *from table1 where id In(select id from table2......);
9、select ...into table...(高级)
(可用select...into outfile...;insert...selkect...替代)
10、SELECT MAX(field1) AS field1 FROM table1 列的最大值
其中：表：table /字段：field

二、修改：
"update table1 set field1='value1',field2=value2'where fiels3='values3";
UPDATE用新值更新现存表中行的列，SET子句指出哪个列要修改和他们应该被给定的值，WHERE子句，如果

给出，指定哪个行应该被更新，否则所有行被更新。

三、插入：
1、insert into table1 values('field1',field2',...);
INSERT ... VALUES形式的语句基于明确指定的值插入行.
2、replace into tbl_name(1,2,3)values('1','2','3');
REPLACE功能与INSERT完全一样，除了如果在表中的一个老记录具有在一个唯一索引上的新记录有相同的值

，在新记录被插入之前，老记录被删除。

四、删除：
$a="delet from table1 where field1='$value1' and field2='$value2'";
DELETE从tbl_name表中删除满足由where_definition给出的条件的行，并且返回删除记录的个数。如果你执

行一个没有WHERE子句的DELETE，所有行都被删除。

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