Little experience sharing-database

Use of char and varchar

1. If the length of the data to be stored in the column is almost the same, you should consider using char; otherwise, you should consider using varchar.
   For example: ID number, order number, phone number.
2. If the maximum data length in the column is less than 50Byte, generally consider using char.
   (Of course, if this column is rarely used, based on the consideration of saving space and reducing I/O, you can still choose to use varchar)
3. Generally, it is not appropriate to define a char type column larger than 50Byte.

Comparison of MyISAM and InnoDB

Comparison item	MyISAM	InnoDB
Primary foreign key	not support	stand by
Affairs	not support	stand by
Row table lock	Table lock, even if one record is operated, the entire table will be locked, which is not suitable for high concurrency	Row lock, during operation, only one row is locked without affecting other rows, suitable for high concurrency
Cache	Only cache indexes, not real data	Not only caches indexes, but also caches real data, which requires high memory, and memory size has a decisive impact on performance
Table space	small	Big
focus point	performance	Affairs
Default installation	Yes	Yes