基础SELECT实例

SELECT查询语句

　　---进行单条记录、多条记录、单表、多表、子查询……

SELECT [ALL | DISTINCT | DISTINCTROW ] [HIGH_PRIORITY] [MAX_STATEMENT_TIME = N] [STRAIGHT_JOIN] [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT] [SQL_CACHE | SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS] select_expr [, select_expr ...] [FROM table_references [PARTITION partition_list] [WHERE where_condition] [GROUP BY {col_name | expr | position} [ASC | DESC], ... [WITH ROLLUP]] [HAVING where_condition] [ORDER BY {col_name | expr | position} [ASC | DESC], ...] [LIMIT {[offset,] row_count | row_count OFFSET offset}] [PROCEDURE procedure_name(argument_list)] [INTO OUTFILE 'file_name' [CHARACTER SET charset_name] export_options | INTO DUMPFILE 'file_name'
      | INTO var_name [, var_name]] [FOR UPDATE | LOCK IN SHARE MODE]]

select书写使用技巧：

　　①确认须要访问数据来自哪几张表

　　　　from来自某张表或者某几张表

　　　　join添加某张表

　　　　on表链接条件

　　记住一点：每关联一个表就须要加上对应的on条件（on条件就是主外键条件）

　　②经过where条件过滤数据

　　③确认需求里面是否有分组聚合的含义

　　　　分组：group by

　　　　聚合：聚合函数

　　　　聚合条件过滤：having

　　④是否须要排序

　　　　order by

 

一、查询某张表全部数据

mysql> select * from temp; 解析：*表明全部列，temp表明表名，不带条件就查询全部数据

 

二、查询指定列和条件的数据

mysql> select name,age from temp where age = 22; 解析：查询name和age这两列，age 等于22的数据。

 

三、对查询的数据进行运算操做

mysql> select age+2,age/2,age-2,age*2 from temp where age-2 > 22; mysql> select PLAYRNO,AMOUNT,AMOUNT*6.5 “Ren Min Bi” from PENALTIES; 解析：查询AMOUNT列数据乘6.5并改列名为Ren Min Bi 使用小括号能够改变运算的优先级

 

四、concat函数，字符串链接

mysql> select NAME,concat(TOWN,STREET,HOUSENO) “player Home Address” from PLAYERS; 解析：利用concat函数将TOWN,STREET,HOUSENO三列的字符串链接起来，别名列为player Home Address(能够在concat里加' '进行分隔) 注意：concat和null进行链接，会致使链接后的数据成为null mysql> select * from t1; +------+--------+--------+
| id   | First  | Last   |
+------+--------+--------+
|    1 | zhang  | jiacai |
|    2 | linghu | NULL   |
+------+--------+--------+ mysql> select id,concat(First,' ',Last) from t1; +------+------------------------+
| id   | concat(First,' ',Last) |
+------+------------------------+
|    1 | zhang jiacai           |
|    2 | NULL                   |
+------+------------------------+

concat_ws函数，指定分隔符的字符串链接

mysql> select id,concat_ws(':',First,Last) "Full Name" from t1; +------+--------------+
| id   | Full Name    |
+------+--------------+
|    1 | zhang:jiacai |
|    2 | linghu       |
+------+--------------+ 圆括号里的第一个位置用来指定字符串链接的分隔符

 

五、as 列别名(或省略，留空格)

mysql> select id as 'num' from t1; mysql> select id 'num',First from t1;

 

六、distinct关键字去掉重复数据

mysql> select * from t2; +------+
| num  |
+------+
|    1 |
|    1 |
|    1 |
|    2 |
+------+ mysql> select distinct num from t2; +------+
| num  |
+------+
|    1 |
|    2 |
+------+ distinct 多列：去重的是同行多列组合的重复数据 mysql> select distinct id, age from temp;

 

七、where条件查询

where语句中的条件比较：大于>、大于等于>=、小于<、小于等于<=、等于=、不等于<> mysql> select * from tableName where a>2 or a>=3 or a<5 or a<=6 or a=7 or a<>0;

 

八、and 而且、or 或者、not非

mysql> select * from temp where age>20 and name=‘jack’; 解析：查询name等于jack而且年龄大于20的 mysql> select * from tmep where name=‘jack’ or name=‘jackson’; 解析：查询name是jack或是jackson的 mysql> select * from temp where not (age > 20); 解析：取小于等于20的数据 mysql> select * from temp where id not in(1, 2); 解析：查询id数不是1，也不是2的

 

九、between v1 and v2：v1和v2之间

mysql> select * form temp where age between 20 and 25; 解析：查询age在20和25之间的

 

十、in 查询：多个条件 相似于or

mysql> select * from temp where id in (1, 2, 3); 解析：查询id在括号中出现的数据

 

十一、like 模糊查询

%:替代0个或多个字符 _：替代一个字符 mysql> select * from temp where name like ‘j%’; 解析：查询name以j开头的(%通配全部) mysql> select * from temp where name like ‘%k%’; 解析：查询name包含k的 escape转义 mysql> select * from temp where name like ‘\_%’ escape ‘\’; 解析：指定\为转义字符，上面的就能够查询name中以“_”开头的数据

 

十二、is null、is not null

mysql> select * from temp where name is null; 解析：查询为null的数据 mysql> select * from temp where name is not null; 解析：查询不为null的数据

 

1三、order by排序：desc降序、asc升序

mysql> select * from temp order by id; (默认asc升排序) mysql> select * from temp order by id desc; (指定降序排) 多列组合 mysql> select * from temp order by id, age;

 

1四、limit子句：从结果集中选取最前面或最后面的几行

　　一般和order by连用，放其后面

limit  <获取的行数> [OFFSET <跳过的行数>]

limit [<跳过的行数>,] <获取的行数> 

mysql> select playerno,name from players order by playerno asc limit 3,5; mysql> select playerno,name from players order by playerno asc limit 5 offset 3; 解析：跳过前面的3行，从第4行开始取，取5行

注意：MySQL5.7 doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery'

 

1五、group by、having 分组聚合

select [聚合函数] 字段名 from 表名

　　[where 查询条件]

　　[group by 字段名]

　　[having 过滤条件]

mysql> select salary,count(*) from salary_tab -> where salary>=2000
    -> group by salary -> having count(*)>=0; +---------+----------+
| salary  | count(*) |
+---------+----------+
| 2000.00 |        1 |
| 3000.00 |        1 |
+---------+----------+

 

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