问题
I have a table in DB and it is approx 90 GB in space. I tried to count no of rows in the table
select count(idNewsNotification) from notification and it resulted
4982397
1 row in set (59 min 48.35 sec)
But when I queried using show table status like <table_name> it is showing that
Engine: InnoDB
Version: 10
Row_format: Compact
Rows: 8631267
Avg_row_length: 11237
Data_length: 96996425728
Max_data_length: 0
Index_length: 175374336
Data_free: 0
Auto_increment: NULL
.....
What is the perfect procedure for knowing the no of records in the table ?
回答1:
The fact that your count took an hour implies that you're running InnoDB (which doesn't cache this data).
As such, the table status is an approximation based on other factors, and is not to be trusted.
The count(*) would be accurate, but a pain to wait for.
From the doc:
Some storage engines, such as MyISAM, store the exact count. For other storage engines, such as InnoDB, this value is an approximation, and may vary from the actual value by as much as 40 to 50%. In such cases, use SELECT COUNT(*) to obtain an accurate count.
回答2:
This is not a good one, in some cases.
For InnoDB tables, the row count is only a rough estimate used in SQL optimization. (This is also true if the InnoDB table is partitioned.)
TEST:
I have the same db (dumped and imported on different server) both innoDB
Same table:
Server One: 49,231
Server Two: 53,242
49231 is not correct and You can see this table with "~" mark in phpmyadmin
来源：https://stackoverflow.com/questions/12966538/will-show-table-status-display-exact-rows-in-the-table