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SQL Group Functions

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.

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SQL Group Functions

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  1. SQL Group Functions Introduction to Oracle9i: SQL

  2. 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 Introduction to Oracle9i: SQL

  3. 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 Introduction to Oracle9i: SQL

  4. 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 Introduction to Oracle9i: SQL

  5. 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 Introduction to Oracle9i: SQL

  6. SUM Function Calculates total amount stored in a numeric column for a group of rows Introduction to Oracle9i: SQL

  7. AVG Function Calculates average of numeric values in a specified column Introduction to Oracle9i: SQL

  8. COUNT Function Two purposes: • Count non-NULL values • Count total records, including those with NULL values Introduction to Oracle9i: SQL

  9. COUNT Function – Non-NULL Values Include column name in argument to count number of occurrences Introduction to Oracle9i: SQL

  10. COUNT Function – NULL Values Include asterisk in argument to count number of rows Introduction to Oracle9i: SQL

  11. MAX Function Returns largest value Introduction to Oracle9i: SQL

  12. MIN Function Returns smallest value Introduction to Oracle9i: SQL

  13. 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 Introduction to Oracle9i: SQL

  14. GROUP BY Example Introduction to Oracle9i: SQL

  15. HAVING Clause// Serves as the WHERE clause for grouped data Introduction to Oracle9i: SQL

  16. Order of Clause Evaluation When included in the same SELECT statement, evaluated in order of: • WHERE • GROUP BY • HAVING Introduction to Oracle9i: SQL

  17. Nesting Functions • Inner function resolved first • Maximum nesting depth: 2 Introduction to Oracle9i: SQL

  18. Statistical Group Functions • Based on normal distribution • Includes: • STDDEV • VARIANCE Introduction to Oracle9i: SQL

  19. STDDEV Function Calculates standard deviation for grouped data Introduction to Oracle9i: SQL

  20. VARIANCE Function Determines data dispersion within a group Introduction to Oracle9i: SQL

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