MySQL under COUNT (*) and Count (column) distinguish performance comparison

COUNT (*) calculates the number of rows, including null

Count (column) calculates the number of rows for a particular column's value, and does not contain null values.

Count () is also used, and the use of Count (1) is the same as the result of Count (*).

about their performance issues

1. In any case select COUNT (*) from TableName is the optimal choice;
2. Minimize the query of select COUNT (*) from tablename WHERE COL = ' value ';
3. Eliminate the appearance of select COUNT (COL) from tablename WHERE COL2 = ' value '.

If the table does not have a primary key, then count (1) is faster than count (*).
If you have a primary key, count (primary key, union primary key) is faster than count (*).
If the table has only one field, COUNT (*) is the fastest.