OOW2016: Exploring Advanced SQL Techniques Using Analytic Functions

Zohar Elkayam www.realdbamagic.com Twitter: @realmgic Exploring Advanced SQL Techniques Using Analytic Functions

Who am I? • Zohar Elkayam, CTO at Brillix • DBA, team leader, database trainer, public speaker, and a senior consultant for over 18 years • Oracle ACE Associate • Blogger – www.realdbamagic.com and www.ilDBA.co.il 2

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Agenda: Advanced SQL • “Basic” aggregation extensions: Rollup, Cube, and Grouping Sets • Analytic functions • Reporting Functions • Ranking Functions • Inter-row Functions • Oracle 12c new features overview • Top-N queries • Pattern matching (Match Recognize Syntax) 7

Advanced Aggregation More than just group by… 8

Basics • Group functions will return a single row for each group of rows • We can run group functions only when we group the rest of the columns together using GROUP BY clause • Common group functions: SUM, MIN, MAX, AVG, etc. • We can filter out rows after aggregation, if we use the HAVING clause 9

• Use ROLLUP or CUBE with GROUP BY to produce super aggregate rows by cross-referencing columns • ROLLUP grouping produces a result set containing the regular grouped rows and the subtotal and grand total values • CUBE grouping produces a result set containing the rows from ROLLUP and cross-tabulation rows 10 GROUP BY With the ROLLUP and CUBE Operators

The ROLLUP Operator • ROLLUP is an extension of the GROUP BY clause • Use the ROLLUP operation to produce cumulative aggregates, such as subtotals SELECT [column,] group_function(column). . . FROM table [WHERE condition] [GROUP BY [ROLLUP] group_by_expression] [HAVING having_expression]; [ORDER BY column]; ` 11

Using the ROLLUP Operator: Example SELECT department_id, job_id, SUM(salary) FROM hr.employees WHERE department_id < 60 GROUP BY ROLLUP(department_id, job_id); 1 2 3 Total by DEPARTMENT_ID and JOB_ID Total by DEPARTMENT_ID Grand total 12

The CUBE Operator • CUBE is an extension of the GROUP BY clause • You can use the CUBE operator to produce cross-tabulation values with a single SELECT statement SELECT [column,] group_function(column)... FROM table [WHERE condition] [GROUP BY [CUBE] group_by_expression] [HAVING having_expression] [ORDER BY column]; 13

SELECT department_id, job_id, SUM(salary) FROM hr.employees WHERE department_id < 60 GROUP BY CUBE (department_id, job_id); . . . Using the CUBE Operator: Example 14 1 2 3 4 Grand total Total by JOB_ID Total by DEPARTMENT_ID and JOB_ID Total by DEPARTMENT_ID

The GROUPING SETS Operator • The GROUPING SETS syntax is used to define multiple groupings in the same query • All groupings specified in the GROUPING SETS clause are computed and the results of individual groupings are combined with a UNION ALL operation • Grouping set efficiency: • Only one pass over the base table is required • There is no need to write complex UNION statements • The more elements GROUPING SETS has, the greater the potential of a performance benefit 15

SELECT department_id, job_id, manager_id, AVG(salary) FROM hr.employees GROUP BY GROUPING SETS ((department_id,job_id), (job_id,manager_id)); Using GROUPING SETS: Example . . . 1 2 16

Composite Columns • A composite column is a collection of columns that are treated as a unit. ROLLUP (a,(b,c), d) • Use parentheses within the GROUP BY clause to group columns, so that they are treated as a unit while computing ROLLUP or CUBE operators. • When used with ROLLUP or CUBE, composite columns require skipping aggregation across certain levels. 17

SELECT department_id, job_id, manager_id, SUM(salary) FROM hr.employees WHERE department_id < 50 GROUP BY CUBE ( department_id,(job_id, manager_id)); Composite Columns: Example 18 1 2 3 4

Analytic Functions Let’s analyze our data! 19

Overview of SQL for Analysis and Reporting • Oracle has enhanced SQL's analytical processing capabilities by introducing a family of analytic SQL functions • These analytic functions enable you to calculate and perform: • Reporting operations (MIN, MAX, COUNT) • Rankings and percentiles (RANK, ROW_NUMBER) • Moving window calculations • Inter-row calculations (LAG/LEAD, FIRST/LAST etc.) • Pivoting operations (11g) • Pattern matching (12c) • Linear regression and predictions 20

Why Use Analytic Functions? • Ability to see one row from another row in the results • Avoid self-join queries and simplify the queries • Summary data in detail rows • Slice and dice within the results • Different function can use different grouping sets • Performance improvement, in some cases 21

Concepts Used in Analytic Functions • Result set partitions: These are created and available to any aggregate results such as sums and averages. The term “partitions” is unrelated to the table partitions feature. • Window: For each row in a partition, you can define a sliding window of data, which determines the range of rows used to perform the calculations for the current row. • Current row: Each calculation performed with an analytic function is based on a current row within a partition. It serves as the reference point determining the start and end of the window. 22

Reporting Functions • We can use aggregative/group functions as analytic functions (i.e. SUM, AVG, MIN, MAX, COUNT etc.) • Each row will get the aggregative value for a given partition without the need for group by clause so we can have multiple group by’s on the same row • Getting the raw data along with the aggregated value • Use Order By to get cumulative aggregations 23

Reporting Functions Examples 24 SELECT last_name, salary, department_id, ROUND(AVG(salary) OVER (PARTITION BY department_id),2) AVG, COUNT(*) OVER (PARTITION BY manager_id) CNT, SUM(salary) OVER (PARTITION BY department_id ORDER BY salary) SUM, MAX(salary) OVER () MAX FROM hr.employees;

Using the Ranking Functions • A ranking function computes the rank of a record compared to other records in the data set based on the values of a set of measures. The types of ranking function are: • RANK and DENSE_RANK functions • ROW_NUMBER function • PERCENT_RANK function • NTILE function 26

Working with the RANK Function • The RANK function calculates the rank of a value in a group of values, which is useful for top-N and bottom-N reporting. • When using the RANK function, ascending is the default sort order, which you can change to descending. • Rows with equal values for the ranking criteria receive the same rank. • Oracle Database then adds the number of tied rows to the tied rank to calculate the next rank. RANK ( ) OVER ( [query_partition_clause] order_by_clause ) 27

Using RANK: Example SELECT department_id, last_name, salary, RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) "Rank" FROM employees WHERE department_id = 60 ORDER BY department_id, "Rank", salary; 28

RANK and DENSE_RANK: Example SELECT department_id, last_name, salary, RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) "Rank", DENSE_RANK() over (partition by department_id ORDER BY salary DESC) "Drank" FROM employees WHERE department_id = 60 ORDER BY department_id, salary DESC, "Rank" DESC; DENSE_RANK ( ) OVER ([query_partition_clause] order_by_clause) 29

Working with the ROW_NUMBER Function • The ROW_NUMBER function calculates a sequential number of a value in a group of values. • When using the ROW_NUMBER function, ascending is the default sort order, which you can change to descending. • Rows with equal values in the ranking criteria might receive different values across executions. ROW_NUMBER ( ) OVER ( [query_partition_clause] order_by_clause ) 30

ROW_NUMBER VS. ROWNUM • ROWNUM is a pseudo column, ROW_NUMBER is an actual function • ROWNUM is calculated when the result returns to the client so it requires sorting of the entire dataset in order to return an ordered list • ROW_NUMBER will only sort the required rows thus giving better performance • ROW_NUMBER can use grouping 31

Using the PERCENT_RANK Function • Uses rank values in its numerator and returns the percent rank of a value relative to a group of values • PERCENT_RANK of a row is calculated as follows: • The range of values returned by PERCENT_RANK is 0 to 1, inclusive. The first row in any set has a PERCENT_RANK of 0. The return value is NUMBER. Its syntax is: (rank of row in its partition - 1) / (number of rows in the partition - 1) PERCENT_RANK () OVER ([query_partition_clause] order_by_clause) 32

Using PERCENT_RANK: Example SELECT department_id, last_name, salary, PERCENT_RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) AS pr FROM hr.employees ORDER BY department_id, pr, salary; 33

Working with the NTILE Function • Not really a ranking function • Divides an ordered data set into a number of buckets indicated by expr, and assigns the appropriate bucket number to each row • The buckets are numbered 1 through expr NTILE ( expr ) OVER ([query_partition_clause] order_by_clause) 34

Summary of Ranking Functions • Different ranking functions may return different results if the data has ties SELECT last_name, salary, department_id, ROW_NUMBER() OVER (PARTITION BY department_id ORDER BY salary DESC) A, RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) B, DENSE_RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) C, PERCENT_RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) D, NTILE(4) OVER (PARTITION BY department_id ORDER BY salary DESC) E FROM hr.employees; 35

Inter-row Analytic Functions 36

Using the LAG and LEAD Analytic Functions • LAG provides access to more than one row of a table at the same time without a self-join. • Given a series of rows returned from a query and a position of the cursor, LAG provides access to a row at a given physical offset before that position. • If you do not specify the offset, its default is 1. • If the offset goes beyond the scope of the window, the optional default value is returned. If you do not specify the default, its value is NULL. {LAG | LEAD}(value_expr [, offset ] [, default ]) OVER ([ query_partition_clause ] order_by_clause) 37

Using LAG and LEAD: Example SELECT time_id, TO_CHAR(SUM(amount_sold),'9,999,999') AS SALES, TO_CHAR(LAG(SUM(amount_sold),1) OVER (ORDER BY time_id),'9,999,999') AS LAG1, TO_CHAR(LEAD(SUM(amount_sold),1) OVER (ORDER BY time_id),'9,999,999') AS LEAD1 FROM sales WHERE time_id >= TO_DATE('10-OCT-2000') AND time_id <= TO_DATE('14-OCT-2000') GROUP BY time_id; 38

Using FIRST_VALUE/LAST_VALUE • Returns the first/last value in an ordered set of values • If the first value in the set is null, then the function returns NULL unless you specify IGNORE NULLS. This setting is useful for data densification. 39 FIRST_VALUE (expr [ IGNORE NULLS ]) OVER (analytic_clause) LAST_VALUE (expr [ IGNORE NULLS ]) OVER (analytic_clause)

Using FIRST_VALUE: Example SELECT department_id, last_name, salary, FIRST_VALUE(last_name) OVER (ORDER BY salary ASC ROWS UNBOUNDED PRECEDING) AS lowest_sal, LAST_VALUE(last_name) OVER (ORDER BY salary ASC ROWS BETWEEN UNBOUNDED PRECEDING and UNBOUNDED FOLLOWING) AS highest_sal FROM (SELECT * FROM employees WHERE department_id = 30 ORDER BY employee_id) ORDER BY department_id, last_name, salary; 40

Using NTH_VALUE Analytic Function • Returns the N-th values in an ordered set of values • Different default window: RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW 41 NTH_VALUE (measure_expr, n) [ FROM { FIRST | LAST } ][ { RESPECT | IGNORE } NULLS ] OVER (analytic_clause)

Using NTH_VALUE: Example SELECT prod_id, channel_id, MIN(amount_sold), NTH_VALUE ( MIN(amount_sold), 2) OVER (PARTITION BY prod_id ORDER BY channel_id ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) nv FROM sh.sales WHERE prod_id BETWEEN 13 and 16 GROUP BY prod_id, channel_id; 42

Using the LISTAGG Function • For a specified measure, LISTAGG orders data within each group specified in the ORDER BY clause and then concatenates the values of the measure column • WARNING: Limited to output of 4000 chars (else, error message in runtime) 43 LISTAGG(measure_expr [, 'delimiter']) WITHIN GROUP (order_by_clause) [OVER query_partition_clause]

Using LISTAGG: Example SELECT department_id "Dept", hire_date "Date", last_name "Name", LISTAGG(last_name, ', ') WITHIN GROUP (ORDER BY hire_date, last_name) OVER (PARTITION BY department_id) as "Emp_list" FROM hr.employees WHERE hire_date < '01-SEP-2003' ORDER BY "Dept", "Date", "Name"; 44

Window Functions • The windowing_clause gives some analytic functions a further degree of control over this window within the current partition • The windowing_clause can only be used if an order_by_clause is present • The windows are always limited to the current partition • Generally, the default window is the entire work set unless stated otherwise 46

Windowing Clause Useful Usages • Cumulative aggregation • Sliding average over proceeding and/or following rows • Using the RANGE parameter to filter aggregation records 47

Windows Can Be By RANGE or ROWS 48 Possible values for start_point and end_point UNBOUNDED PRECEDING The window starts at the first row of the partition. Only available for start points. UNBOUNDED FOLLOWING The window ends at the last row of the partition. Only available for end points. CURRENT ROW The window starts or ends at the current row value_expr PRECEDING A physical or logical offset before the current row. When used with RANGE, can also be an interval literal value_expr FOLLOWING As above, but an offset after the current row RANGE BETWEEN start_point AND end_point ROWS BETWEEN start_point AND end_point

Shortcuts • Useful shortcuts for the windowing clause: 49 ROWS UNBOUNDED PRECEDING ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ROWS 10 PRECEDING ROWS BETWEEN 10 PRECEDING AND CURRENT ROW ROWS CURRENT ROW ROWS BETWEEN CURRENT ROW AND CURRENT ROW (1 row)

Oracle 12c New Feature Overview Just a couple, we can talk for hours about all the new features..  50

What’s New in Oracle 12c • Top-N Queries and pagination: returning the top-n queries • Compatible with ANSI SQL • synthetic honey – just a syntax enhancement, not performance enhancement • Pattern matching: New MATCH_RECOGNIZE syntax for finding row between patterns 51

Top-N Examples 52 SELECT last_name, salary FROM hr.employees ORDER BY salary FETCH FIRST 4 ROWS ONLY; SELECT last_name, salary FROM hr.employees ORDER BY salary FETCH FIRST 4 ROWS WITH TIES; SELECT last_name, salary FROM hr.employees ORDER BY salary DESC FETCH FIRST 10 PERCENT ROWS ONLY;

What is Pattern Matching? • A new syntax that allows us to identify and group rows with consecutive values • Consecutive in this regards – row after row (must be ordered) • Uses regular expression like syntax to find patterns • Finds complex behavior we couldn’t find before, or needed PL/SQL to do it (for example: V-shape, U-shape, and others)! 53

Example: Sequential Employee IDs • Our goal: find groups of users with sequences IDs • This can be useful for detecting missing employees in a table, or to locate “gaps” in a group 54 FIRSTEMP LASTEMP ---------- ---------- 7371 7498 7500 7520 7522 7565 7567 7653 7655 7697 7699 7781 7783 7787 7789 7838

SELECT * FROM Emps MATCH_RECOGNIZE ( ORDER BY emp_id PATTERN (STRT B*) DEFINE B AS emp_id = PREV(emp_id)+1 ONE ROW PER MATCH MEASURES STRT.page firstemp, LAST(page) lastemp AFTER MATCH SKIP PAST LAST ROW ); 1. Define input 2. Pattern Matching 3. Order input 4. Process pattern 5. Using defined conditions 6. Output: rows per match 7. Output: columns per row 8. Where to go after match? Pattern Matching Example 55

1. Define input 2. Pattern Matching 3. Order input 4. Process pattern 5. Using defined conditions 6. Output: rows per match 7. Output: columns per row 8. Where to go after match? Pattern Matching Example (actual syntax) SELECT * FROM Emps MATCH_RECOGNIZE ( ORDER BY emp_id MEASURES STRT.emp_id firstemp, LAST(emp_id) lastemp ONE ROW PER MATCH AFTER MATCH SKIP PAST LAST ROW PATTERN (STRT B*) DEFINE B AS emp_id = PREV(emp_id)+1 ); 56

Oracle 11g Analytic Function Solution 57 select firstemp, lastemp From (select nvl (lag (r) over (order by r), minr) firstemp, q lastemp from (select emp_id r, lag (emp_id) over (order by emp_id) q, min (emp_id) over () minr, max (emp_id) over () maxr from emps e1) where r != q + 1 -- groups including lower end union select q, nvl (lead (r) over (order by r), maxr) from ( select emp_id r, lead (emp_id) over (order by emp_id) q, min (emp_id) over () minr, max (emp_id) over () maxr from emps e1) where r + 1 != q -- groups including higher end );

Summary • We talked about advanced aggregation clauses, multi- dimensional aggregation, and how utilizing it can save us time and effort • Analytic functions are really important both for performance and for code clarity • We saw how reporting and rank function work and how to use them • We explored some Oracle 12c enhancements – more information about that can be found in my blog: www.realdbamagic.com 59

Thank You! Zohar Elkayam twitter: @realmgic Zohar@Brillix.co.il www.realdbamagic.com 60

OOW2016: Exploring Advanced SQL Techniques Using Analytic Functions

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OOW2016: Exploring Advanced SQL Techniques Using Analytic Functions