在MySQL 5.7中,支持两种Generated Column,即Virtual Generated Column和Stored Generated Column,前者只将Generated Column保存在数据字典中(表的元数据),并不会将这一列数据持久化到磁盘上;后者会将Generated Column持久化到磁盘上,而不是每次读取的时候计算所得。很明显,后者存放了可以通过已有数据计算而得的数据,需要...
INSERT INTO table1 VALUES (123, 'even more text',default,'something'); Query OK, 1 row affected, 2 warnings (0.00 sec) Warning (Code 1645): The value specified for computed column 'd' in table 'table1' ignored. Warning (Code 1265): Data truncated for column 'd' at row 1 SELECT ...
下面是一个使用mermaid语法表示的状态图,描述了整个过程的流程: 创建包含VirtualColumn的表创建虚拟列添加索引使用虚拟列进行查询 结论 在本文中,我详细介绍了MySQL Virtual Column能否加索引的问题以及如何实现。通过创建包含Virtual Column的表、创建虚拟列、添加索引和使用虚拟列进行查询,我们可以充分利用Virtual Column的...
很明显,后者存放了可以通过已有数据计算而得的数据,需要更多的磁盘空间,与Virtual Column相比并没有优势,因此,MySQL 5.7中,不指定Generated Column的类型,默认是Virtual Column。 如果需要Stored Generated Golumn的话,可能在Virtual Generated Column上建立索引更加合适 综上,一般情况下,都使用Virtual Generated Column,这...
The idea is very simple: if we store a column MySQL 1 `FlightDate` date in our table we may want to filter or group by year(FlightDate), month(FlightDate) or even dayofweek(FlightDate). The “brute-force” approach: use the above Date and Time MySQL functions in the query; however...
virtual column In mysql5.7, two types of virtual columns are supported: virtual columns and stored columns. The difference between the two is that virtual only calculates the results when reading rows, but does not physically store them, so it does not occupy storage space, and only builds sec...
mysql> insert into t values(2, POINT(-75.341621, 41.061987), POINT(-75.3215434, 41.0595024)); Query OK, 1 row affected (0.04 sec) Now you want to measure the distance (in meters) between the two points. You can quickly ADD a virtual column and then index it, all without having to re...
MySQL从5.7开始支持generated column,相关worklog为:WL#411: Generated columns。与常规字段的值不同,此类列的值不是由用户设置的,而是根据创建 GC 时用户给出的表达式计算得出的。生成的列有两种类型 - 存储列和虚拟列。当插入新记录或更新旧记录时,前一个值仅计算一次。计算后,该值将以与常规字段的值完全相同的...
1 select_type: SIMPLE table: features partitions: NULL type: ref possible_keys: feature_street key: feature_street key_len: 33 ref: const rows: 808 filtered: 100.00 Extra: NULL 1 row in set, 1 warning (0.00 sec) # Using the virtual column mysql> EXPLAIN SELECT * FROM features WHERE ...
mysql 5.7+ 版本开始支持 json 数据类型,可以方便的存储JSON格式的数据,同时配合虚拟列 (virtual generated column),可以方便的为 json 列数据的某属性映射虚拟列,建立索引,高效检索。 构造json数据 方法:json_array() / json_object() json_array / json_object 用于组装 json 数据,json 说的简单些json就是由...