MySQL vs SQLServer
kenttanl opened this issue · comments
数据类型映射关系
| No | SQL Server | MySQL | Range | Storage(Bytes) | Comment |
|---|---|---|---|---|---|
| 1 | INT | INT | MS SQL : -2^31 |
4 | |
| 2 | TINYINT | TINYINT | MS SQL : 0 |
1 | UNSIGNED flag set in MySQL. |
| 3 | SMALLINT | SMALLINT | MS SQL : -2^15 |
2 | |
| 4 | BIGINT | BIGINT | MS SQL : -2^63 |
8 | |
| 5 | BIT | TINYINT(1) | 0, 1, NULL | MS SQL : 1~2MySQL : 1 | Microsoft SQL Server Type Mapping |
| 6 | FLOAT(n) | FLOAT(p) | MS SQL-FLOAT(n)的n值single-precision:1-24double-precision:0-23MySQL-FLOAT(p)的p值single-precision:25-53double-precision:24-53 | single-precision:4double-precision:8 | Precision value is used for storage size in both. |
| 7 | REAL | FLOAT | float(24) | 4 | |
| 8 | NUMERIC(p,s) | DECIMAL(M,D) | MS SQL-NUMERIC(p,s):(有效位數,小數位數)p:1-38MySQL-DECIMAL(M,D):(有效位數,小數位數)M:1-65 | MS SQLPrecisionNumber of Bytes1-9510-19920-281329-3817MySQLLeftover DigitsNumber of Bytes0 01–213–4 25–637–9 4 | 1-9 |
| 9 | DECIMAL(p,s) | DECIMAL(M,D) | MS SQL-DECIMAL同No.8的NUMERICMySQL-DECIMAL同No.8的DECIMAL | ||
| 10 | MONEY | DECIMAL | MS SQL-MONEY-922,337,203,685,477.5808 到 922,337,203,685,477.5807MySQL-同No.8的DECIMAL | 8 | |
| 11 | SMALLMONEY | DECIMAL | MS SQL-SMALLMONEY- 214,748.3648 到 214,748.3647MySQL-同No.8的DECIMAL | 4 | |
| 12 | CHAR(n) | CHAR(n)/LONGTEXT | MS SQL-CHAR(n)n:1-8000MySQL-CHAR(n)n:0-255 | CHAR: n個位元組MySQL-LONGTEXTL + 4 bytes, L < 2^32 | MySQLDepending on its length. MySQL Server 5.6 and higher can have CHAR columns with a length up to 255 characters. Anything larger is migrated as LONGTEXT.LONGTEXT: L represents the actual length in bytes of a given string value. |
| 13 | NCHAR(n) | CHAR(n) CHARACTER SET utf8mb4/LONGTEXT | MS SQL-NCHAR(n)n:1-4000MySQL-CHAR(n)n:0-255 | MS SQL-NCHARn*2 個位元組MySQL-CHARn個位元組 | MySQLDepending on its length. MySQL Server 5.6 and higher can have VARCHAR columns with a length up to 65535 characters. Anything larger is migrated to one of the TEXT blob types. In MySQL, a character set of strings depends on the column character set instead of the data type.NCHAR/NVARCHAR implies the character set UTF8MB3, which will be replaced by UTF8MB4 in a future release.Please consider using CHAR(x) CHARACTER SET UTF8MB4 in order to be unambiguoushttps://bugs.mysql.com/bug.php?id=76529 |
| 14 | VARCHAR(n) | VARCHAR(n)/MEDIUMTEXT/LONGTEXT | MS SQL-VARCHAR(n)n:1-8000MySQL-VARCHAR(n)n:0-65535 | MS SQL-VARCHAR實際儲存的位元組+ 2 位元組MySQL-VARCHARn<255,實際儲存的位元組+ 1 位元組n>=255,實際儲存的位元組+ 2 位元組MySQL-MEDIUMTEXTL + 3 bytes, L < 2^24MySQL-LONGTEXTL + 4 bytes, L < 2^32 | MySQLDepending on its length. MySQL Server 5.6 and higher can have VARCHAR columns with a length up to 65535 characters. Anything larger is migrated to one of the TEXT blob types.MEDIUMTEXT/LONGTEXT: L represents the actual length in bytes of a given string value. |
| 15 | NVARCHAR(n) | VARCHAR(N) CHARACTER SET utf8mb4MEDIUMTEXT/LONGTEXT | MS SQL-NVARCHAR(n)n:1-4000MySQL-VARCHAR(n)n:0-65535 | MS SQL-NVARCHAR實際儲存的位元組*2+ 2 位元組MySQL-VARCHARn<255,實際儲存的位元組+ 1 位元組n>=255,實際儲存的位元組+ 2 位元組MySQL-同No.14的MEDIUMTEXT/LONGTEXT | Depending on its length. MySQL Server 5.6 and higher can have VARCHAR columns with a length up to 65535 characters. Anything larger is migrated to one of the TEXT blob types. In MySQL, a character set of strings depends on the column character set instead of the data type. |
| 16 | DATE | DATE | MS SQL0001-01-01 to 9999-12-31MySQL1000-01-01 to 9999-12-31 | 3 | |
| 17 | DATETIME(p) | DATETIME(p) | MS SQL1753-1-1 to 9999-12-31 00:00:00.000 到 23:59:59.997MySQL1000-01-01 00:00:00.000000 to 9999-12-31 23:59:59.999999 | MS SQL8MySQLMySQL 5.6.4以前:8 bytesMySQL 5.6.4以後:5 bytes + fractional seconds storageFractional Seconds PrecisionStorage Required00 bytes1, 21 byte3, 42 bytes5, 63 bytes | 0 |
| 18 | DATETIME2(p) | DATETIME(p) | MS SQL-DATETIME20001-01-01 00:00:00.0000000 to 9999-12-31 23:59:59.9999999MySQL-同No.17的DATETIME | MS SQLp<3: 6 bytesp=3 or p=4: 7 bytesother: 8 bytes. | |
| 19 | SMALLDATETIME | DATETIME | MS SQL-SMALLDATETIME1900-01-01 00:00:00 to 2079-06-06 23:59:59MySQL-同No.17的DATETIME | MS SQL4 | |
| 20 | DATETIMEOFFSET | DATETIME | MS SQL-DATETIMEOFFSET0001-01-01 00:00:00.00.0000000 to 9999-12-31 23:59:59.9999999MySQL-同No.17的DATETIME | MS SQL10 bytes, fixed is the default with the default of 100ns fractional second precision. | |
| 21 | TIME(p) | TIME(p) | MS SQL-TIME00:00:00.0000000 to 23:59:59.9999999MySQL-TIME-838:59:59.000000 to 838:59:59.000000 | MS SQL5 bytes, fixed, is the default with the default of 100ns fractional second precision.MySQLMySQL 5.6.4以前:3 bytesMySQL 5.6.4以後:3 bytes + fractional seconds storageFractional Seconds PrecisionStorage Required00 bytes1, 21 byte3, 42 bytes5, 63 bytes | 0 |
| 22 | TIMESTAMP | TIMESTAMP | |||
| 23 | ROWVERSION | TIMESTAMP | |||
| 24 | BINARY | BINARY/MEDIUMBLOB/LONGBLOB | Depending on its length. | ||
| 25 | VARBINARY | VARBINARY/MEDIUMBLOB/LONGBLOB | Depending on its length. | ||
| 26 | TEXT | VARCHAR/MEDIUMTEXT/LONGTEXT | Depending on its length. | ||
| 27 | NTEXT | VARCHAR/MEDIUMTEXT/LONGTEXT | Depending on its length. | ||
| 28 | IMAGE | TINYBLOB/MEDIUMBLOB/LONGBLOB | Depending on its length. | ||
| 29 | SQL_VARIANT | not migrated | There is not specific support for this data type. | ||
| 30 | TABLE | not migrated | There is not specific support for this data type. | ||
| 31 | HIERARCHYID | not migrated | There is not specific support for this data type. | ||
| 32 | UNIQUEIDENTIFIER | VARCHAR(64) | A unique flag set in MySQL. There is not specific support for inserting unique identifier values. | ||
| 33 | SYSNAME | VARCHAR(160) | |||
| 34 | XML | TEXT |
简单语法对比
| 操作类型 | MySQL | SQL Server | Note |
|---|---|---|---|
| 表中添加列（DDL） | ALTER TABLE tablename ADD COLUMN columnname type[first/after columnname] | ALTER TABLE tablename ADD columnname type | 在MySQL中可以指定新列的位置，SQL Server只能默认加在最后 |
| 表中添加索引（DDL） | CREATE INDEX indexname ON tablename(columnname) | CREATE INDEX indexname ON tablename(columnname) | |
| 当列上有索引时，修改列属性（DDL） | ALTER TABLE tablename MODIFY COLUMN columnname type | DROP INDEX indexname ON tablenameALTER TABLE tablename ALTER COLUMN coluname typeCREATE INDEX indexname ON tablename(columnname) | 在MySQL中，某个列有索引，如果我们想修改这个列，是直接进行修改；在SQL Server中，某个列有索引，如果我们想修改这个列，必须先删除索引，修改列，最后再将索引加回 |
| 修改表中列顺序（DDL） | ALTER TABLE tablename MODIFY columnname type first/after | 不支持 | |
| 重命名表（DDL） | ALTER TABLE tablename RENAME TO newtable_name | EXEC SP_RENAME 'tablename','newtablename' | |
| 同时更新多表数据（DML） | UPDATE tablenamea a,tablenameb b SET a.columnname=xxx,b.columnname=yyy WHERE a.xx=b.xx | 不支持 | |
| 查询前几条数据（DML） | SELECT * FROM tablename LIMIT 10; | SELECT TOP 10 * FROM tablename | |
| 数据组合成新数据（DML） | SELECT CONCAT('DROP TABLE ','table_name',';') FROM tables WHERE table_schema='test1' | SELECT 'DROP TABLE '+name +';' FROM test1.sys.tables |
关于 CHAR/VARCHAR 的差异
在 MySQL 中，仅当列定义为 VARCHAR，并且插入数据时尾部带有空格，将该值作为 WHERE 条件时需要带上对应的空格，否则不会返回数据。
其他三种情况（定义为 CHAR 且插入数据尾部不带空格，定义为 CHAR 且插入数据尾部带空格，定义为 VARCHAR 且插入数据尾部不带空格），将该值作为 WHERE 条件时仅需传入实际数据（如果插入数据时带有空格，作为条件查询时也无需带上空格）。如果传入了带有尾部空格的数据作为查询条件，不会有结果返回。
在SQL Server中，不管是四种情况中哪一种，均可只传入实际数据作为 WHERE 条件，并且得到数据返回
简单差异描述
| 对比点 | MySQL | SQL Sever |
|---|---|---|
| 兼容性支持 | 支持多平台操作系统 | 虽然提供多平台，但是最主要还是在Windows，非Windows平台某些功能缺失 |
| 开发语言支持 | 支持多种开发语言 | 支持多种开发语言 |
| 存储引擎 | 支持多种存储引擎，当前推荐InnoDB | 没有存储引擎概念 |
| 成本因素 | 开源免费 | 商业软件 |
| IDE工具 | 多种工具 | 以SSMS为主，丰富的功能 |
| 安全因素 | 服务运行时文件可被其他进程访问修改 | 服务运行时无法被其他进程访问修改，相对更安全 |
| 备份还原 | 相对繁琐，但是更灵活 | 非常简单，但是备份最小单位是数据库 |
| 开发维护 | Oracle。同时存在其他分支 | 微软 |
| SQL语法 | 简单易用 | 相对更复杂 |
| 多国语言支持 | 只有英语版本 | 多国语言均支持 |
【强制要求】在 MySQL 中仅需选择 VARCHAR 类型，禁止选择 NCHAR 或者 NVARCHAR 类型
解读：因为我们已经设置数据库的字符集为 UTF8mb4，已经能存储多国语言了。一旦我们设置字段类型为 NCHAR 或者NVARCHAR, MySQL 会自动将这个列转为 CHAR 或者 VARCHAR，同时将该列字符集转成 UTF8mb3，也即常规的 UTF8, 该列的字符集就会与数据库默认字符集相异。
