<left_table> <join_type> JOIN <right_table> ON <join_condition> WHERE <where_condition> GROUP BY <group_by_list> HAVING <having_condition> ORDER BY <order_by_condition> LIMIT <limit_number>二 SELECT语句关键字的执行顺序(7) SELECT (8) DISTINCT <select_list> (1) FROM <left_table> (3) <join_type> JOIN <right_table> (2) ON <join_condition> (4) WHERE <where_condition> (5) GR...
10) NOT NULL,city VARCHAR(10) NOT NULL,PRIMARY KEY(customer_id))ENGINE=INNODB DEFAULT CHARSET=UTF8;CREATE TABLE table2(order_id INT NOT NULL auto_increment,customer_id VARCHAR(10),PRIMARY KEY(order_id))ENGINE=INNODB DEFAULT CHARSET=UTF8;创建表 3.插入测试数据 INSERT INTO table1(customer_id,city) VALUES(‘163‘,‘hangzhou‘); INSERT INTO table1(customer_id,city) VALUES(‘9you‘,‘shanghai‘); INSERT...
对于一条sql 语句，用到很多关键词 SELECT FROM JOIN WHERE GROUP BY HAVING ORDER BY LIMIT，在命名时候不能和这些关键词重名，下面分别讲述意思。 1，select 查询语句命令行 SELECT之后是逗号分隔列或星号(*)的列表，表示要返回所有列 2，from 命令行 FROM指定要查询数据的表或视图。 3，JOIN 命令行 根据某些连接条件从其他表中获取数据。 4，WHERE 条件判断 WHERE过滤结果集中的行。 5，GROUP BY 分组将一组行组合成小分...
语法 SELECT column_1, column_2, ... FROMtable_1 [INNER | LEFT |RIGHT] JOIN table_2 ON conditions WHEREconditions GROUP BY column_1 HAVING group_conditions ORDER BY column_1 LIMIT offset, length;参考资料 易百教程 select 语句 SELECT语句由以下列表中所述的几个子句组成： SELECT之后是逗号分隔列或星号(*)的列表，表示要返回所有列。 FROM指定要查询数据的表或视图。 JOIN根据某些连接条件从其他表中获取数据。 WHE...
查看当前正在运行的sql语句执行最时间：select * from information_schema.PROCESSLIST where info is not null order by time desc ;查看当前有那些表在使用：show OPEN TABLES where In_use > 0;查看与innodb事务先关的语句：SELECT FROM INFORMATION_SCHEMA.INNODB_LOCKS; SELECT from INFORMATION_SCHEMA.INNODB_TRX;SELECT * FROM INFORMATION_SCHEMA.INNODB_LOCK_WAITS; 查看当前数据库的链接情况：SELECT count(*) AS cou...
: 联合查询 /*union 联合合并: 将多条查询语句的结果合并成一个结果语法: 查询语句1 union 查询语句2 union ...应用语境: 要查询的结果来自多个表,但查询的列数的列信息一致时,可将最终结果归于一个表中注意: 需要自己将所有的字段名自己按顺序摆放; */#引入的案例 : 查询部门编号 > 90 或邮箱包含a的员工信息SELECT * FROM employees WHERE email LIKE ‘%a%‘ OR department_id > 90;SELECT * FROM employees WHERE email LIKE...
1、一条SQL语句查询两表中两个字段 首先描述问题,student表中有字段startID，endID。garde表中的ID需要对应student表中的startID或者student表中的endID才能查出grade表中的name字段，这时候问题就来了，如果需要一条sql一句同时查出garde表中的两条数据怎么办？(两表的关联字段为 SID)sql="select b.name,c.name as name2 from student a,garde b,grade c where a.SID=b.SID and a.SID=c.SID and a.startID=b.ID and a.endID=b.ID...
from information_schema.tables where table_schema=‘csdb‘ and table_type=‘base table‘;table_schema：用于限定数据库名称，此处我用了自建的csdb库，你查用你的，注意：information_schema表示系统库。table_type=‘base table‘：限定只查询基表。 2：查询指定数据库中指定表的所有字段名column_name select column_name from information_schema.columns where table_schema=‘csdb‘ and table_name=‘...
<left_table> <join_type> JOIN <right_table> ON <join_condition> WHERE <where_condition> GROUP BY <group_by_list> HAVING <having_condition> ORDER BY <order_by_condition> LIMIT <limit_number>二. SELECT语句关键字的执行顺序(7) SELECT (8) DISTINCT <select_list> (1) FROM <left_table> (3) <join_type> JOIN <right_table> (2) ON <join_condition> (4) WHERE <where_condition> (5) ...
SELECT DISTINCT <select_list> FROM <left_table> <join_type> JOIN <right_table> ON <join_condition> WHERE <where_condition> GROUP BY <group_by_list> HAVING <having_condition> ORDER BY <order_by_condition> LIMIT <limit_number>二 SELECT语句关键字的执行顺序(7) SELECT (8) DISTINCT <select_list> (1) FROM <left_table> (3) <join_type> JOIN <right_table> (2) ON <join_condition> (4) ...
MariaDB安装方式：包管理器(rpm, deb)通用二进制格式；源码编译安装；SQL：数据库、表、索引、视图、存储过程、存储函数、触发器、事件调度器、用户和权限；元数据数据库：库名为mysqlMYSQL语句：有2种DDL, DMLDDL: CREATE, ALTER, DROPDML: INSERT, DELETE, UPDATE, SELECTDCL: GRANT（授权）, REVOKE（撤销授权）MariaDB程序的组成：C/S架构C：Clientmysql：CLI交互式客户端程序；mysqldump：逻辑备份工具；mysqladmin：管理工具...
-- 查询全部内容 SELECT * FROM sc; -- 查询部分列 SELECT zno,sno,sname FROM student; -- 限制条件查询部分列 SELECT zno,sno,sname,ssex FROM student WHERE ssex = 女; -- 限制查询条数 SELECT zno,sno,sname,ssex FROM student WHERE ssex = 女 LIMIT 6; -- 列别名和表别名：可读性增加，简洁性 as可以省略 SELECT zno as 专业代号,sno as 学号,sname 姓名,ssex 性别 FROM student WHERE ssex = 女 LIMIT 6; -- DISTINCT避免重...
我是前端，但总有需求让做后端的活，所以顺带着熟悉了下简单的查询语句 贴出来，如果有需要可以参考下，备注很详细，就不多解释了废话不多说贴代码： #去除unionid 重复的搜索结果 #query_resultsign 表名 select *, count(unionid) from query_resultsign where issign=‘false‘ group by unionid ;#去除unionid 重复的搜索结果 #query_resultsign 表名 select *, count(unionid) from query_resultsign where issign=‘true‘ g...
import pymysqlclass MysqldbHelper(object): def __init__(self, host="192.168.1.243", username="devlop", password="devlop", port=3306, database=‘zl_dcms‘, charset=‘utf8‘): self.host = host self.username = username self.password = password self.database = database self.port = port self.con = None ...
MySQL嵌套查询语句统计每个省的人口最多的与最少的城市 SELECT District,NAME,Population FROM city WHERE Population IN (SELECT MIN(Population) FROM city WHERE city.CountryCode=‘CHN‘ GROUP BY city.District) UNION SELECT District,NAME,Population FROM city WHERE Population IN (SELECT MAX(Population) FROM city WHERE city.CountryCode=‘CHN‘ GROUP BY city.District)MySQL嵌套查询语句标签：mysq 嵌套 mi...