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MySQL Load Data 的多种用法
。
1、LOAD 基本背景
我们在数据库运维过程中难免会涉及到需要对文本数据进行处理,并导入到数据库中,本文整理了一些导入导出时常见的场景进行示例演示.
2、LOAD 基础参数
文章后续示例均使用以下命令导出的 csv 格式样例数据(以 , 逗号做分隔符,以 " 双引号作为界定符) 。
- -- 导出基础参数
- select * into outfile '/data/mysql/3306/tmp/employees.txt'
- character set utf8mb4
- fields terminated by ','
- enclosed by '"'
- lines terminated by ' '
- from employees.employees limit 10;
-
- -- 导入基础参数
- load data infile '/data/mysql/3306/tmp/employees.txt'
- replace into table demo.emp
- character set utf8mb4
- fields terminated by ','
- enclosed by '"'
- lines terminated by ' '
- ...
3、LOAD 示例数据及示例表结构
以下为示例数据,表结构及对应关系信息 。
- -- 导出的文件数据内容
- [root@10-186-61-162 tmp]# cat employees.txt
- "10001","1953-09-02","Georgi","Facello","M","1986-06-26"
- "10002","1964-06-02","Bezalel","Simmel","F","1985-11-21"
- "10003","1959-12-03","Parto","Bamford","M","1986-08-28"
- "10004","1954-05-01","Chirstian","Koblick","M","1986-12-01"
- "10005","1955-01-21","Kyoichi","Maliniak","M","1989-09-12"
- "10006","1953-04-20","Anneke","Preusig","F","1989-06-02"
- "10007","1957-05-23","Tzvetan","Zielinski","F","1989-02-10"
- "10008","1958-02-19","Saniya","Kalloufi","M","1994-09-15"
- "10009","1952-04-19","Sumant","Peac","F","1985-02-18"
- "10010","1963-06-01","Duangkaew","Piveteau","F","1989-08-24"
-
- -- 示例表结构
- SQL > desc demo.emp;
- +-------------+---------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +-------------+---------------+------+-----+---------+-------+
- | emp_no | int | NO | PRI | NULL | |
- | birth_date | date | NO | | NULL | |
- | first_name | varchar(16) | NO | | NULL | |
- | last_name | varchar(16) | NO | | NULL | |
- | fullname | varchar(32) | YES | | NULL | | -- 表新增字段,导出数据文件中不存在
- | gender | enum('M','F') | NO | | NULL | |
- | hire_date | date | NO | | NULL | |
- | modify_date | datetime | YES | | NULL | | -- 表新增字段,导出数据文件中不存在
- | delete_flag | char(1) | YES | | NULL | | -- 表新增字段,导出数据文件中不存在
- +-------------+---------------+------+-----+---------+-------+
-
- -- 导出的数据与字段对应关系
- emp_no birth_date first_name last_name gender hire_date
- "10001" "1953-09-02" "Georgi" "Facello" "M" "1986-06-26"
- "10002" "1964-06-02" "Bezalel" "Simmel" "F" "1985-11-21"
- "10003" "1959-12-03" "Parto" "Bamford" "M" "1986-08-28"
- "10004" "1954-05-01" "Chirstian" "Koblick" "M" "1986-12-01"
- "10005" "1955-01-21" "Kyoichi" "Maliniak" "M" "1989-09-12"
- "10006" "1953-04-20" "Anneke" "Preusig" "F" "1989-06-02"
- "10007" "1957-05-23" "Tzvetan" "Zielinski" "F" "1989-02-10"
- "10008" "1958-02-19" "Saniya" "Kalloufi" "M" "1994-09-15"
- "10009" "1952-04-19" "Sumant" "Peac" "F" "1985-02-18"
- "10010" "1963-06-01" "Duangkaew" "Piveteau" "F" "1989-08-24"
4、LOAD 场景示例
场景1. LOAD 文件中的字段比数据表中的字段多 。
只需要文本文件中部分数据导入到数据表中 。
- -- 临时创建2个字段的表结构
- SQL > create table emp_tmp select emp_no,hire_date from emp;
- SQL > desc emp_tmp;
- +-----------+------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +-----------+------+------+-----+---------+-------+
- | emp_no | int | NO | | NULL | |
- | hire_date | date | NO | | NULL | |
- +-----------+------+------+-----+---------+-------+
-
- -- 导入数据语句
- load data infile '/data/mysql/3306/tmp/employees.txt'
- replace into table demo.emp_tmp
- character set utf8mb4
- fields terminated by ','
- enclosed by '"'
- lines terminated by ' '
- (@C1,@C2,@C3,@C4,@C5,@C6) -- 该部分对应employees.txt文件中6列数据
- -- 只对导出数据中指定的2个列与表中字段做匹配,mapping关系指定的顺序不影响导入结果
- set hire_date=@C6,
- emp_no=@C1;
-
- -- 导入数据结果示例
- SQL > select * from emp_tmp;
- +--------+------------+
- | emp_no | hire_date |
- +--------+------------+
- | 10001 | 1986-06-26 |
- | 10002 | 1985-11-21 |
- | 10003 | 1986-08-28 |
- | 10004 | 1986-12-01 |
- | 10005 | 1989-09-12 |
- | 10006 | 1989-06-02 |
- | 10007 | 1989-02-10 |
- | 10008 | 1994-09-15 |
- | 10009 | 1985-02-18 |
- | 10010 | 1989-08-24 |
- +--------+------------+
- 10 rows in set (0.0016 sec)
场景 2. LOAD 文件中的字段比数据表中的字段少 。
表字段不仅包含文本文件中所有数据,还包含了额外的字段 。
- -- 导入数据语句
- load data infile '/data/mysql/3306/tmp/employees.txt'
- replace into table demo.emp
- character set utf8mb4
- fields terminated by ','
- enclosed by '"'
- lines terminated by ' '
- (@C1,@C2,@C3,@C4,@C5,@C6) -- 该部分对应employees.txt文件中6列数据
- -- 将文件中的字段与表中字段做mapping对应,表中多出的字段不做处理
- set emp_no=@C1,
- birth_date=@C2,
- first_name=@C3,
- last_name=@C4,
- gender=@C5,
- hire_date=@C6;
。
场景3. LOAD 生成自定义字段数据 。
从场景 2 的验证可以看到,emp 表中新增的字段 fullname,modify_date,delete_flag 字段在导入时并未做处理,被置为了 NULL 值,如果需要对其进行处理,可在 LOAD 时通过 MySQL支持的函数 或给定 固定值 自行定义数据,对于文件中存在的字段也可做函数处理,结合导入导出,实现简单的 ETL 功能,如下所示:
- -- 导入数据语句
- load data infile '/data/mysql/3306/tmp/employees.txt'
- replace into table demo.emp
- character set utf8mb4
- fields terminated by ','
- enclosed by '"'
- lines terminated by ' '
- (@C1,@C2,@C3,@C4,@C5,@C6) -- 该部分对应employees.txt文件中6列数据
-
- -- 以下部分明确对表中字段与数据文件中的字段做Mapping关系,不存在的数据通过函数处理生成(也可设置为固定值)
- set emp_no=@C1,
- birth_date=@C2,
- first_name=upper(@C3), -- 将导入的数据转为大写
- last_name=lower(@C4), -- 将导入的数据转为小写
- fullname=concat(first_name,' ',last_name), -- 对first_name和last_name做拼接
- gender=@C5,
- hire_date=@C6 ,
- modify_date=now(), -- 生成当前时间数据
- delete_flag=if(hire_date<'1988-01-01','Y','N'); -- 对需要生成的值基于某一列做条件运算
场景4. LOAD 定长数据 。
定长数据的特点如下所示,可以使用函数取出字符串中固定长度来生成指定列数据 。
- SQL > select
- c1 as sample_data,
- substr(c1,1,3) as c1,
- substr(c1,4,3) as c2,
- substr(c1,7,2) as c3,
- substr(c1,9,5) as c4,
- substr(c1,14,3) as c5,
- substr(c1,17,3) as c6 from t1
-
- *************************** 1. row ***************************
- sample_data: ABC余振兴CDMySQLEFG数据库
- c1: ABC
- c2: 余振兴
- c3: CD
- c4: MySQL
- c5: EFG
- c6: 数据库
定长数据导入需要明确每列数据占用的字符个数,以下直接使用 rpad 对现有的表数据填充空格的方式生成定长数据用作示例使用 。
- -- 生成定长数据
- SQL > select
- concat(rpad(emp_no,10,' '),
- rpad(birth_date,19,' '),
- rpad(first_name,14,' '),
- rpad(last_name,16,' '),
- rpad(gender,2,' '),
- rpad(hire_date,19,' ')) as fixed_length_data
- from employees.employees limit 10;
-
- +----------------------------------------------------------------------------------+
- | fixed_length_data |
- +----------------------------------------------------------------------------------+
- | 10001 1953-09-02 Georgi Facello M 1986-06-26 |
- | 10002 1964-06-02 Bezalel Simmel F 1985-11-21 |
- | 10003 1959-12-03 Parto Bamford M 1986-08-28 |
- | 10004 1954-05-01 Chirstian Koblick M 1986-12-01 |
- | 10005 1955-01-21 Kyoichi Maliniak M 1989-09-12 |
- | 10006 1953-04-20 Anneke Preusig F 1989-06-02 |
- | 10007 1957-05-23 Tzvetan Zielinski F 1989-02-10 |
- | 10008 1958-02-19 Saniya Kalloufi M 1994-09-15 |
- | 10009 1952-04-19 Sumant Peac F 1985-02-18 |
- | 10010 1963-06-01 Duangkaew Piveteau F 1989-08-24 |
- +----------------------------------------------------------------------------------+
-
- -- 导出定长数据
- select
- concat(rpad(emp_no,10,' '),
- rpad(birth_date,19,' '),
- rpad(first_name,14,' '),
- rpad(last_name,16,' '),
- rpad(gender,2,' '),
- rpad(hire_date,19,' ')) as fixed_length_data
- into outfile '/data/mysql/3306/tmp/employees_fixed.txt'
- character set utf8mb4
- lines terminated by ' '
- from employees.employees limit 10;
-
- -- 导出数据示例
- [root@10-186-61-162 tmp]# cat employees_fixed.txt
- 10001 1953-09-02 Georgi Facello M 1986-06-26
- 10002 1964-06-02 Bezalel Simmel F 1985-11-21
- 10003 1959-12-03 Parto Bamford M 1986-08-28
- 10004 1954-05-01 Chirstian Koblick M 1986-12-01
- 10005 1955-01-21 Kyoichi Maliniak M 1989-09-12
- 10006 1953-04-20 Anneke Preusig F 1989-06-02
- 10007 1957-05-23 Tzvetan Zielinski F 1989-02-10
- 10008 1958-02-19 Saniya Kalloufi M 1994-09-15
- 10009 1952-04-19 Sumant Peac F 1985-02-18
- 10010 1963-06-01 Duangkaew Piveteau F 1989-08-24
-
- -- 导入定长数据
- load data infile '/data/mysql/3306/tmp/employees_fixed.txt'
- replace into table demo.emp
- character set utf8mb4
- fields terminated by ','
- enclosed by '"'
- lines terminated by ' '
- (@row) -- 对一行数据定义为一个整体
- set emp_no = trim(substr(@row,1,10)),-- 使用substr取前10个字符,并去除头尾空格数据
- birth_date = trim(substr(@row,11,19)),-- 后续字段以此类推
- first_name = trim(substr(@row,30,14)),
- last_name = trim(substr(@row,44,16)),
- fullname = concat(first_name,' ',last_name), -- 对first_name和last_name做拼接
- gender = trim(substr(@row,60,2)),
- hire_date = trim(substr(@row,62,19)),
- modify_date = now(),
- delete_flag = if(hire_date<'1988-01-01','Y','N'); -- 对需要生成的值基于某一列做条件运算
5、LOAD 总结
1.默认情况下导入的顺序以文本文件 列-从左到右,行-从上到下 的顺序导入 。
2.如果表结构和文本数据不一致,建议将文本文件中的各列依次顺序编号并与表中字段建立 mapping 关系,以防数据导入到错误的字段 。
3.对于待导入的文本文件较大的场景,建议将文件 按行拆分 为多个小文件,如用 split 拆分 。
4.对文件导入后建议执行以下语句验证导入的数据是否有 Warning,ERROR 以及导入的数据量 。
-
GET DIAGNOSTICS @p1=NUMBER,@p2=ROW_COUNT;
-
select @p1 AS ERROR_COUNT,@p2 as ROW_COUNT;
5.文本文件数据与表结构存在过大的差异或数据需要做清洗转换,建议还是用专业的 ETL 工具或先粗略导入 MySQL 中再进行加工转换处理 。
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原文链接:https://blog.csdn.net/ActionTech/article/details/115212340 。
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