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aggregate function query

The greatest feature of aggregate functions is that they evaluate a value from a set of data. The result value of the aggregate function is calculated only from non-NULL values in the selected row; NULL values are ignored.

COUNT() function

COUNT() function returns the number of rows in the selected set that are not NULL values for any parameter except "*"; returns the number of all rows in the selected set that contain NULL values for parameter "*." COUNT(*) without a WHERE clause is internally optimized to quickly return the total number of all records in the table.

Examples:

select COUNT(*) from info;

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SUM() function

The SUM() function sums the values of a field in a table.

Examples:

select SUM(score) from info;

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AVG() function

The AVG() function averages the values of a field in a table.

Examples:

select avg(score) from info;

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MAX() function

The MAX() function can find the maximum value of a field in a table.

Examples:

select max(score) from info;

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MIN() function

The MIN() function finds the minimum value of a field in a table.

Examples:

select min(score) from info;

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