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Sql group functions



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    Sql group functions Sql group functions Presentation Transcript

    • SQL Group Functions
    • Chapter Objectives
      • Differentiate between single-row and multiple-row functions
      • Use the SUM and AVG functions for numeric calculations
      • Use the COUNT function to return the number of records containing non-NULL values
      • Use COUNT(*) to include records containing NULL values
    • Chapter Objectives
      • Use the MIN and MAX functions with non-numeric fields
      • Determine when to use the GROUP BY clause to group data
      • Identify when the HAVING clause should be used
      • List the order of precedence for evaluating WHERE, GROUP BY, and HAVING clauses
    • Chapter Objectives
      • State the maximum depth for nesting group functions
      • Nest a group function inside a single-row function
      • Calculate the standard deviation and variance of a set of data, using the STDDEV and VARIANCE functions
    • Group Functions
      • Return one result per group of rows processed
      • Also called multiple-row and aggregate functions
      • All group functions ignore NULL values except COUNT(*)
      • Use DISTINCT to suppress duplicate values
    • SUM Function
      • Calculates total amount stored in a numeric column for a group of rows
    • AVG Function
      • Calculates average of numeric values in a specified column
    • COUNT Function
      • Two purposes:
        • Count non-NULL values
        • Count total records, including those with NULL values
    • COUNT Function – Non-NULL Values
      • Include column name in argument to count number of occurrences
    • COUNT Function – NULL Values
      • Include asterisk in argument to count number of rows
    • MAX Function
      • Returns largest value
    • MIN Function
      • Returns smallest value
    • GROUP BY Clause
      • Used to group data
      • Must be used for individual column in the SELECT clause with a group function
      • Cannot reference column alias
    • GROUP BY Example
    • HAVING Clause//
      • Serves as the WHERE clause for grouped data
    • Order of Clause Evaluation
      • When included in the same SELECT statement, evaluated in order of:
        • WHERE
        • GROUP BY
        • HAVING
    • Nesting Functions
      • Inner function resolved first
      • Maximum nesting depth: 2
    • Statistical Group Functions
      • Based on normal distribution
      • Includes:
        • STDDEV
        • VARIANCE
    • STDDEV Function
      • Calculates standard deviation for grouped data
    • VARIANCE Function
      • Determines data dispersion within a group