MYSQL's specific usage skills in large numbers of statistics

One, case, then ELSE END use usage.

When you use SQL statements to count the occurrences of a certain state of a field, consider using the case and then ELSE END usage. When the amount of data is too large, it is not recommended.

Example:

SUM ( Case if state=0 then 1 ELSE 0 END ) as Deade

Second, To_char

The time stamp is converted to a date format, and the specific usage scenario can be aggregated by the GROUP by

Example:

To_char (To_timestamp (add_time), ' Yyyy-mm-dd ')

Third, left joins, right join

involves inter-table operations and can be used.

Example:

From a left OUTER JOIN b on A.id=b.mid

IV. Statistical Division of SQL

Occasionally, you need to use the division rules, NUMERIC numeric types, to make statistical ratios.

ROUND(live::numeric/total::numeric,4) as Percentage

MYSQL's specific usage skills in large numbers of statistics