2.MySQL I/O参数MySQL涉及到IO相关的参数会比较多，因此这里仅一部分经常用到的参数：innodb_io_capacity和innodb_io_capacity_max是最直接限制IOPS的指标，大多数时候，SSD 可以设置成16000或者更高的数值，如果是云主机或者其他的共享存储设备，则需要了解一下详细的IOPS上限再具体调整。trx_commit和 sync_binlog这...
For example,TIME(0),TIME(2),TIME(4), andTIME(6)use 3, 4, 5, and 6 bytes, respectively.TIMEandTIME(0)are equivalent and require the same storage. Storage Requirements for String Types In the following table,Mrepresents the declared column length in characters for nonbinary string types a...
VARCHAR(10) CHARACTER SET utf8 NATIONAL VARCHAR(10) NCHAR VARCHAR(10) NATIONAL CHARACTER VARYING(10) NATIONAL CHAR VARYING(10) You can useN'literal'(orn'literal') to create a string in the national character set. These statements are equivalent: SELECT N'some text'; SELECT n'some text'; ...
When a table is created withROW_FORMAT=DYNAMIC,InnoDBcan store long variable-length column values (forVARCHAR,VARBINARY, andBLOBandTEXTtypes) fully off-page, with the clustered index record containing only a 20-byte pointer to the overflow page. Fixed-length fields greater than or equal to 768...
(which is equivalent to 256). If either argument isNULLor the hash length is not one of the permitted values, the return value isNULL. Otherwise, the function result is a hash value containing the desired number of bits. See the notes at the beginning of this section about storing hash ...
标准的SQL中使用NCHAR,NVARCHAR等表示国际字符集。但是MySQL不是,它只有CHAR和VARCHAR。需要通过设置字符集来达到存储存储其他字符的目的。 For example, these data type declarations are equivalent: CHAR(10) CHARACTER SET utf8 NATIONAL CHARACTER(10) NCHAR(10) ...
Yes/NoA logical field can be displayed as Yes/No, True/False, or On/Off. In code, use the constants True and False (equivalent to -1 and 0).Note:Null values are not allowed in Yes/No fields1 bit Ole ObjectCan store pictures, audio, video, or other BLOBs (Binary Large Objects)up...
because the two are logically equivalent. Not so in MySQL, which sorts the values in the IN() list and uses a fast binary search to see whether a value is in the list. This is O(Log n) in the size of the list, whereas an equivalent series of OR clauses is O(n) in the size...
Otherwise, it becomes equivalent to INSERT, because there is no indexto be used to determine whether a new row duplicates another. 3.3 为什么REPLACE INTO操作在binlog日志中记录的是update操作? 这里我们源码文件sql_insert.cc和log_event.cc进行分析。 sql_insertcc: ... /* Check if there ...
To display the privileges granted to the current user (the account you are using to connect to the server), you can use any of the following statements: SHOW GRANTS; SHOW GRANTS FOR CURRENT_USER; SHOW GRANTS FOR CURRENT_USER(); If SHOW GRANTS FOR CURRENT_USER (or any equivalent syntax)...