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SQL 查询优化指南：SELECT、SELECT DISTINCT、WHERE 和 ORDER BY 详解

以下是一些示例：从Customers表中选择CustomerName和City列的数据： SELECT CustomerName, City FROM Customers; 从Customers表中选择所有列的数据...以下是ORDER BY关键字的基本语法： SELECT column1, column2, ... FROM table_name ORDER BY column1, column2, ......以下是一些示例：按价格对产品进行升序排序： SELECT * FROM Products ORDER BY Price; 按价格对产品进行降序排序： SELECT * FROM Products ORDER...BY Price DESC; 按产品名称升序排序： SELECT * FROM Products ORDER BY ProductName; 按产品名称降序排序： SELECT * FROM Products...最后看完如果觉得有帮助，欢迎点赞、收藏和关注

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Cassandra Cqlsh 2

是 Cassandra 的客户端接着上一篇，下面分享一下 Cqlsh 的简单使用方法参考 Cassandra Tools Tip: 当前版本 Cassandra 3.11.1 和 cqlsh 5.0.1...* from system_schema.columns ; keyspace_name | table_name | column_name | clustering_order...Use EXPAND ON to enable. cqlsh> EXPAND on Now Expanded output is enabled cqlsh> select * from system_schema.columns...| 0 type | text (1 rows) cqlsh> select * from system_schema.columns limit 2; @ Row 1...| text (2 rows) cqlsh> EXPAND off Disabled Expanded output. cqlsh> select * from system_schema.columns

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cassandra高级操作之索引、排序以及分页

本次就给大家讲讲cassandra的高级操作：索引、排序和分页；处于性能的考虑，cassandra对这些支持都比较简单，所以我们不能希望cassandra完全适用于我们的逻辑，而是应该将我们的逻辑设计的更适合于...cassandra 一、索引和排序　　Cassandra对查询的支持很弱，只支持主键列及索引列的查询，而且主键列还有各种限制，不过查询弱归弱，但它还是支持索引和排序的。...=1 ORDER BY address ASC; SELECT * FROM teacher WHERE id=1 ORDER BY address ASC, name ASC; SELECT * FROM...ORDER BY address DESC, name DESC; SELECT * FROM tt WHERE id=1 ORDER BY address DESC; SELECT * FROM tt...三、参考 cassandra的索引查询和排序 cassandra2.0 如何实现分页查询

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Cassandra查询操作趟坑记录

BY (age asc, bornDate asc, createDate desc ) 1.主键顺序查询限制 cassandra主键是一个partition key主键和多个clustering...分区主键查询限制 cassandra中分区主键只能以等号或in查询,不能使用范围查询也就是不能以出生日期进行范围查询 select * from employee where bornDate..., 所以这样写就是错误 select * from employee where bornDate in ('1999-01-01','1999-01-02') and name = '张三' order...01') and name = '张三' order by age desc, bornDate desc, createDate asc 或 select * from employee where...bornDate = '1999-01-01' and name = '张三' order by age desc, bornDate desc, createDate asc 6.使用In和Order

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Mybatis + Oracle CRUD

"/> FROM zt_terminal_producer a include refid="ztTerminalProducerJoins"/> WHERE a.id = #{id} select...> findList 获取多条记录 Xml select id="findList" resultType="ZtTerminalProducer" > SELECT include refid...="ztTerminalProducerColumns"/> FROM zt_terminal_producer a include refid="ztTerminalProducerJoins..." > SELECT include refid="ztTerminalProducerColumns"/> FROM zt_terminal_producer a include refid...-- 根据实体名称和字段名称和字段值获取唯一记录 --> select id="findUniqueByProperty" resultType="ZtTerminalProducer" statementType

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.NET ORM核心功能之导航属性- EFCore和 SqlSugar

p.* FROM Person p WHERE EXISTS ( SELECT 1 FROM PersonFile pf INNER JOIN File f ON pf.FileId =...假设您有以下实体：人员（Person）、部门（Department）、职位（Position）、学历（Education）和工作经验（WorkExperience）。...(z1 => z1.Department) .Include(z1 => z1.Position) .Include(z1 => z1.Education) .Include(z1 => z1...//EF CORE查询 var Persons= dbContext.Person .Include(z1 => z1.Department) .Include(z1 => z1.Position)...(s=>s.id==1).ToList()) .IncludesAllFirstLayer().ToList();//自动导航和Order重复

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MySQL - order by和 group by 优化初探

position = ‘dev’ order by age explain select * from employees where name = 'LiLei' and position = 'dev...where name = ‘LiLei’ order by position mysql> explain select * from employees where name = 'LiLei'...再来看一个 ---- 案例三：explain select * from employees where name = ‘LiLei’ order by age , position 这个SQL和案例二的很相似...mysql> explain select * from employees where name = 'LiLei' order by age , position ; +----+--------...* from employees where name = ‘LiLei’ order by position , age 再分析一个，和案例上也很像。

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Cassandra应用实践

修改~/.bashrc 添加Java和Cassandra相关路径的环境变量修改Cassandra的配置。...* FROM t; 2、查询条件 Cassandra查询时只支持主键列及索引列的查询，主键查询必须按照主键顺序指定查询条件。...BY (domain DESC); 可以支持的查询条件 select * from t where domain = ?...select * from t where domain = ? and day = ? select * from t where domain = ? and day > ?...如果要以domain和key作为查询条件，需要加上allow filtering select * from t where domain = ? and key = ?

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Apache Drill 专为Hadoop、NoSQL和云存储设计的Schema-free类型的SQL引擎

* FROM cp....这里有一个示例，通过一个简单的SQL来查询JSON文件中的嵌套元素和数组： SELECT * FROM (SELECT t.trans_id, t.trans_info.prod_id...TPC-H 标准查询： TPC-H第四个语句 SELECT o.o_orderpriority, COUNT(*) AS order_count FROM orders o WHERE o.o_orderdate...这里有一个示例，使用Drill查询Hive表： SELECT `month`, state, sum(order_total) AS sales FROM hive.orders GROUP BY `month...这里有一个示例，将Hive表，HBase表（视图）和JSON文件进行组合查询： SELECT custview.membership, sum(orders.order_total) AS sales

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sqlzoo练习12-more-join

Star Trek movies, include the id, title and yr (all of these movies include the words Star Trek in the...Order results by year. select id, title, yr from movie where title like '%Star Trek%' order by yr; What...movie 和actor两个表是没有直接联系的，只能通过casting表的actorid字段来进行搭桥 select title from movie join casting on movie.id...找出JA演员参加的电影和主演 select title, name -- 找出电影和主演 from movie join casting on (movieid=movie.id and ord...找出和AG合作的全部演员 select name from actor join casting on casting.actorid=actor.id where movieid in (select

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工作中遇到的99%SQL优化，这里都能给你解决方案(二)

EXPLAIN select * from employees WHERE name='LiLei' order by position; ?...EXPLAIN select * from employees WHERE name='LiLei' order by age,position; ?...EXPLAIN select * from employees WHERE name='LiLei' order by position,age; ?...filesort排序 EXPLAIN select * from employees where name='LiLei' order by position; ?...* from employees where name = 'LiLei' order by position; select * from information_schema.OPTIMIZER_TRACE

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MySQL索引（四）常见的索引优化手段

ORDER BY 和 GROUP BY EXPLAIN SELECT * FROM employees WHERE name = 'LiLei' AND position = 'dev' ORDER BY...EXPLAIN SELECT * FROM employees WHERE name = 'LiLei' ORDER BY age,position; 但如果不跳过 age 字段，同样不会使用文件排序，...EXPLAIN SELECT * FROM employees WHERE name = 'LiLei' AND age = 22 ORDER BY position,age; 同样使用上一个排序顺序，...EXPLAIN SELECT * FROM employees WHERE name IN ('LiLei','zhangsan') ORDER BY age, position; 如果使用多个相等条件...EXPLAIN SELECT * FROM employees WHERE name ORDER BY name; --- 覆盖索引优化 EXPLAIN SELECT name,age,position

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MySQL如何选择合适的索引

EXPLAIN select * from employees where name > 'a'; ?...EXPLAIN select name,age,position from employees where name > 'a'; ?...在看另一个case： EXPLAIN select * from employees where name > 'zzz'; ?...name > 'a' ORDER BY position; SELECT * FROM information_schema.OPTIMIZER_TRACE; 查看trace字段： { "steps...SELECT * FROM employees WHERE name > 'zzz' ORDER BY position; SELECT * FROM information_schema.OPTIMIZER_TRACE

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MYSQL回顾（单表查询相关）

; SELECT COUNT(*) FROM employee WHERE depart_id=1; SELECT MAX(salary) FROM employee; SELECT...MIN(salary) FROM employee; SELECT AVG(salary) FROM employee; SELECT SUM(salary) FROM employee...; SELECT SUM(salary) FROM employee WHERE depart_id=3; mysql> select count(dep_id), dep_id from...Having发生在分组group by之后，因而Having中可以使用分组的字段，无法直接取到其他字段,可以使用聚合函数 order by查询排序分为升序ASC和降序DESC mysql> select...where group by having select distinct order by limit ?

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MySQL - 使用trace工具来窥探MySQL是如何选择执行计划的

='员工记录表'; 来看个执行计划 mysql> EXPLAIN select * from employees where name > 'a'; +----+-------------+----...强制走索引（不一定效率高）使用覆盖索引，这样只需要遍历name字段的联合索引树就能拿到所有结果，来看下 mysql> EXPLAIN select name,age,position from...* from employees where name > 'a' order by position; --- 执行SQL mysql> SELECT * FROM information_schema.OPTIMIZER_TRACE...`position` AS `position`,`employees`.`hire_time` AS `hire_time` from `employees` where (`employees`....* from employees where name > 'zzz' order by position; --- 执行SQL mysql> SELECT * FROM information_schema.OPTIMIZER_TRACE

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shading-jdbc 4.1.1 + tk.mybatis + pagehelper 1.3.x +spring boot 2.x 使用注意事项

order_id, order_name, order_date from t_order_logic_0 where order_date='2020-09-06'; 会首先被改写为： select...如上图，加了group by 后，下面的语句 SELECT count(0) FROM (SELECT order_id FROM t_order_logic WHERE order_date = ?...GROUP BY order_id) table_count sharding-jdbc并不能正确解析为t_order_0，仍然还是t_order_logic SELECT count(0) FROM...(SELECT order_id FROM t_order_logic WHERE order_date = ?...1 select id="selectList2" resultMap="BaseResultMap"> 2 select order_id from t_order_logic

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MySQL 查询最后分区

-- MySQL 5.6 select sname,tname,pname,position,method,expression from ( select if (table_schema=@sname...,(select @a:=0,@sname:='',@tname:='') t1 where partition_name is not null order by table_schema,table_name...,partition_ordinal_position desc) t where rn=0; -- MySQL 8 select * from ( select table_schema sname...by partition_ordinal_position desc) rn from information_schema.partitions where partition_name is...not null) t where rn=1 order by sname,pname,position,tname; -- 生成按天分区 select concat('partition

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询mysql所有表数据、字段信息

根据库名获取所有表的信息 SELECT * FROM information_schema....`TABLES` WHERE TABLE_SCHEMA = 'erp'; 根据库名获取所有表名称和表说明 SELECT TABLE_NAME, TABLE_COMMENT FROM...`COLUMNS` WHERE TABLE_SCHEMA = 'erp' ORDER BY TABLE_NAME, ORDINAL_POSITION; view: 根据库名获取所有的库和表字段的基本信息...*,t1.* FROM (select COLUMN_NAME as '字段',COLUMN_DEFAULT as '默认值',IS_NULLABLE as '允许为空',COLUMN_TYPE as...'数据类型', COLUMN_COMMENT as '描述' from information_schema.columns where table_schema =(select database(

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MySQL #{驼峰字段} for MyBatis

# 查找在那个表并生成字段名 SQL SELECT TABLE_SCHEMA, TABLE_NAME, concat('SELECT ', group_concat(COLUMN_NAME ORDER...BY ORDINAL_POSITION SEPARATOR ', ' ) , ' FROM ' , TABLE_SCHEMA, '...ORDINAL_POSITION SEPARATOR ', ')) AS COLUMN_NAMES FROM information_schema.COLUMNS WHERE 1=1 AND TABLE_NAME...BY ORDINAL_POSITION SEPARATOR ',\n') , '\nWHERE col=val;')AS SQLStr FROM information_schema.COLUMNS...ELSE concat_ws(' AS ', COLUMN_NAME, COLUMN_COMMENT) END ORDER BY ORDINAL_POSITION SEPARATOR ',

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【YashanDB 知识库】对比 Oracle 和 YashanDB 对象不一致的方法

如果需要更复杂的对比方法，可采用本文中的对比思路和方法。..., TABLE_OWNER, TABLE_NAME, COLUMN_NAME, COLUMN_POSITION, COLUMN_LENGTH, DESCEND FROM SYS.DBA_IND_COLUMNS..., COLUMN_NAME, POSITION FROM SYS.DBA_CONS_COLUMNS; create table oracle.dba_types as select * from sys.dba_types..., COLUMN_NAME, POSITION FROM SYS.DBA_CONS_COLUMNS; create table yashan.dba_types as select * from sys.dba_types...SYS.DBA_TRIGGERS;4、利用数据库能力，直接对比Oracle用户和YashanDB用户的差异。

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SQL 查询优化指南：SELECT、SELECT DISTINCT、WHERE 和 ORDER BY 详解

Cassandra Cqlsh 2

cassandra高级操作之索引、排序以及分页

Cassandra查询操作趟坑记录

Mybatis + Oracle CRUD

.NET ORM核心功能之导航属性- EFCore和 SqlSugar

MySQL - order by和 group by 优化初探

Cassandra应用实践

Apache Drill 专为Hadoop、NoSQL和云存储设计的Schema-free类型的SQL引擎

sqlzoo练习12-more-join

工作中遇到的99%SQL优化，这里都能给你解决方案(二)

MySQL索引（四）常见的索引优化手段

MySQL如何选择合适的索引

MYSQL回顾（单表查询相关）

MySQL - 使用trace工具来窥探MySQL是如何选择执行计划的

shading-jdbc 4.1.1 + tk.mybatis + pagehelper 1.3.x +spring boot 2.x 使用注意事项

MySQL 查询最后分区

询mysql所有表数据、字段信息

MySQL #{驼峰字段} for MyBatis

【YashanDB 知识库】对比 Oracle 和 YashanDB 对象不一致的方法

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