The SQL Procedure

summary-function

Performs statistical summary calculations.

Restriction: A summary function cannot appear in an ON clause or a WHERE clause.

See also: GROUP BY , HAVING Clause , SELECT Clause , and table-expression

Featured in: Creating a View from a Query's Result , Joining Two Tables and Calculating a New Value , and Counting Missing Values with a SAS Macro

summary-function (<DISTINCT|ALL> sql-expression)

sql-expression is described in sql-expression .

Summarizing Data
Summary functions produce a statistical summary of the entire table or view listed in the FROM clause or for each group specified in a GROUP BY clause. If GROUP BY is omitted, all the rows in the table or view are considered to be a single group. These functions reduce all the values in each row or column in a table to one summarizing or aggregate value. For this reason, these functions are often called aggregate functions. For example, the sum (one value) of a column results from the addition of all the values in the column.

Function Names and the Corresponding Statistics
Some functions have more than one name to accommodate both SAS and SQL conventions:

AVG, MEAN: means or average of values
COUNT, FREQ, N: number of nonmissing values
CSS: corrected sum of squares
CV: coefficient of variation (percent)
MAX: largest value
MIN: smallest value
NMISS: number of missing values
PRT: probability of a greater absolute value of Student's t
RANGE: range of values
STD: standard deviation
STDERR: standard error of the mean
SUM: sum of values
SUMWGT: sum of the WEIGHT variable values(footnote 1)
T: Student's t value for testing the hypothesis that the population mean is zero
USS: uncorrected sum of squares
VAR: variance

For a description and the formulas used for these statistics, see SAS Elementary Statistics Procedures

Counting Rows
The COUNT function counts rows. COUNT(*) returns the total number of rows in a group or in a table. If you use a column name as an argument to COUNT, the result is the total number of rows in a group or in a table that have a nonmissing value for that column. If you want to count the unique values in a column, specify COUNT(DISTINCT column).

If the SELECT clause of a table-expression contains one or more summary functions and that table-expression resolves to no rows, then the summary function results are missing values. The following are exceptions that return zeros:

COUNT(*)

COUNT(<DISTINCT> sql-expression)

NMISS(<DISTINCT> sql-expression)

See Creating a View from a Query's Result and Counting Missing Values with a SAS Macro for examples.

Calculating Statistics Based on the Number of Arguments
The number of arguments specified in a summary function affects how the calculation is performed. If you specify a single argument, the values in the column are calculated. If you specify multiple arguments, the arguments or columns listed are calculated for each row. For example, consider calculations on the following table.

proc sql;
   title 'Summary Table';
   select * from summary;

If you use one argument in the function, the calculation is performed on that column only. If you use more than one argument, the calculation is performed on each row of the specified columns. In the following PROC SQL step, the MIN and MAX functions return the minimum and maximum of the columns they are used with. The SUM function returns the sum of each row of the columns specified as arguments:

proc sql;
    select min(x) as Colmin_x, 
           min(y) as Colmin_y, 
           max(z) as Colmax_z, 
           sum(x,y,z) as Rowsum
       from summary;

Remerging Data
When you use a summary function in a SELECT clause or a HAVING clause, you may see the following message in the SAS log:

NOTE: The query requires remerging summary 
      statistics back with the original
      data.

The process of remerging involves two passes through the data. On the first pass, PROC SQL

calculates and returns the value of summary functions. It then uses the result to calculate the arithmetic expressions in which the summary function participates.
groups data according to the GROUP BY clause.

On the second pass, PROC SQL retrieves any additional columns and rows that it needs to show in the output.

The following examples use the PROCLIB.PAYROLL table (shown in Creating a Table from a Query's Result ) to show when remerging of data is and is not necessary.

The first query requires remerging. The first pass through the data groups the data by Jobcode and resolves the AVG function for each group. However, PROC SQL must make a second pass in order to retrieve the values of IdNumber and Salary.

proc sql outobs=10;
   title 'Salary Information';
   title2 '(First 10 Rows Only)';
   select  IdNumber, Jobcode, Salary, 
           avg(salary) as AvgSalary
      from proclib.payroll
      group by jobcode;

You can change the previous query to return only the average salary for each jobcode. The following query does not require remerging because the first pass of the data does the summarizing and the grouping. A second pass is not necessary.

proc sql outobs=10;
   title 'Average Salary for Each Jobcode';
   select Jobcode, avg(salary) as AvgSalary
   from proclib.payroll
   group by jobcode;

When you use the HAVING clause, PROC SQL may have to remerge data to resolve the HAVING expression.

First, consider a query that uses HAVING but that does not require remerging. The query groups the data by values of Jobcode, and the result contains one row for each value of Jobcode and summary information for people in each Jobcode. On the first pass, the summary functions provide values for the Number, Average Age, and Average Salary columns. The first pass provides everything that PROC SQL needs to resolve the HAVING clause, so no remerging is necessary.

proc sql outobs=10;
title 'Summary Information for Each Jobcode';
title2 '(First 10 Rows Only)';
   select Jobcode,
          count(jobcode) as number 
              label='Number',
          avg(int((today()-birth)/365.25))
              as avgage format=2. 
              label='Average Age',
          avg(salary) as avgsal format=dollar8.
              label='Average Salary'
      from proclib.payroll
      group by jobcode
      having avgage ge 30;

In the following query, PROC SQL remerges the data because the HAVING clause uses the SALARY column in the comparison and SALARY is not in the GROUP BY clause.

proc sql outobs=10;
title 'Employees who Earn More than the';
title2 'Average for Their Jobcode';
title3 '(First 10 Rows Only)';
   select Jobcode, Salary, 
          avg(salary) as AvgSalary
      from proclib.payroll
      group by jobcode
      having salary > AvgSalary;

Keep in mind that PROC SQL remerges data when

the values returned by a summary function are used in a calculation. For example, the following query returns the values of X and the percent of the total for each row. On the first pass, PROC SQL computes the sum of X, and on the second pass PROC SQL computes the percentage of the total for each value of X:
```
proc sql;
   title 'Percentage of the Total';
   select X, (100*x/sum(X)) as Pct_Total
      from summary;
```
the values returned by a summary function are compared to values of a column that is not specified in the GROUP BY clause. For example, the following query uses the PROCLIB.PAYROLL table. PROC SQL remerges data because the column Salary is not specified in the GROUP BY clause:
```
proc sql;
   select  jobcode,  salary, 
           avg(salary) as avsal
      from proclib.payroll
      group by jobcode
      having salary > avsal;
```
a column from the input table is specified in the SELECT clause and is not specified in the GROUP BY clause. This rule does not refer to columns used as arguments to summary functions in the SELECT clause.
For example, in the following query, the presence of IdNumber in the SELECT clause causes PROC SQL to remerge the data because IdNumber is not involved in grouping or summarizing during the first pass. In order for PROC SQL to retrieve the values for IdNumber, it must make a second pass through the data.
```
proc sql;
   select IdNumber, jobcode, 
          avg(salary) as avsal
      from proclib.payroll
      group by jobcode;
```

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Restriction:	A summary function cannot appear in an ON clause or a WHERE clause.
See also:	GROUP BY , HAVING Clause , SELECT Clause , and table-expression
Featured in:	Creating a View from a Query's Result , Joining Two Tables and Calculating a New Value , and Counting Missing Values with a SAS Macro

	COUNT(*)
	COUNT(<DISTINCT> sql-expression)
	NMISS(<DISTINCT> sql-expression)