原文: The numberofdifferent valuesina table column.When queries refer to columns that have an associated index,the cardinalityofeach column influences which access method is most efficient.For example,fora columnwitha unique constraint,the numberofdifferent values is equal to the numberofrowsinthe ta...
Using the "not equal to" operator can lead to full table scans, especially on large datasets. Consider indexing columns that are frequently filtered with this operator to improve query performance. Common Mistakes: NULL Values:Remember that comparisons with NULL do not return true. For example, '...
This causes the binary log position and filename of the master to be appended to the dumped data output. Setting the value to 1, will printit as a CHANGE MASTER command in the dumped data output; if equal to 2, that command will be prefixed with a comment symbol. This option will tu...
Not unique table/alias: '%s' • Error number: 1067; Symbol: ER_INVALID_DEFAULT; SQLSTATE: 42000 Message: Invalid default value for '%s' • Error number: 1068; Symbol: ER_MULTIPLE_PRI_KEY; SQLSTATE: 42000 Message: Multiple primary key defined • Error number: 1069; Symbol: ER_TOO...
depend on the existence of a column but that do not actually use its value. CHAR(0) is also quite nice when you need a column that can take only two values: A column that is defined as CHAR(0) NULL occupies only one bit and can take only the values NULL and '' (the empty ...
add-locksTRUE表示在生成表中数据的 insert into`table_name`values(...)之前生成LOCKTABLES`tab`WRITE;语句 commentsTRUE表示生成备注,就是所有--开头的说明,比如:--Dumping dataforfortable`tab`.最好还是启用; create-optionsTRUE表示在生成表结构时会生成:ENGINE=InnoDBAUTO_INCREMENT=827DEFAULTCHARSET=utf8;附加...
log_queries_not_using_indexes:是否记录所有未使用索引的查询语句,默认为OFF。 log_slow_admin_statements:慢速管理语句是否写入慢日志中,管理语句包含 ALTER TABLE,ANALYZE TABLE, CHECK TABLE,CREATE INDEX, DROP INDEX,OPTIMIZE TABLE,REPAIR TABLE,默认为OFF即不写入。
[USER ERROR] Must and only contains AND joined EQUAL-TO predicates of all columns within the primary key: 严格的DELETE where条件检查,请联系技术支持更改系统配置。 20023 [USER ERROR] column was not found: column=xxx INSERT语句中,目标列不存在,请修改。 20024 [USER ERROR] column was not found:...
If you need to insure that values having the maximum possible length can be stored in such a column, you should make sure that the column can accommodate at least 288 characters (255 for the user name and 32 for the host name, plus 1 for the separator@). For this reason—while it is...
because such values often do compress well, and might therefore require feweroverflow pagesas described inSection 17.9.1.5, “How Compression Works for InnoDB Tables”. For general tablespaces, aKEY_BLOCK_SIZEvalue equal to theInnoDBpage size is not permitted. For more information, seeSection 17.6...