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To ANSI or Not To ANSI

To ANSI or Not To ANSI. Gravenstein, Costello, Maurer Amtrust Bank Session #420. Speaker Qualifications. Rumpi Gravenstein, Application Developer, Senior, Amtrust Bank Newsletter Editor, North East Ohio Oracle Users Group Has been working with Oracle since 1988

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To ANSI or Not To ANSI

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  1. To ANSI or Not To ANSI Gravenstein, Costello, Maurer Amtrust Bank Session #420

  2. Speaker Qualifications • Rumpi Gravenstein, Application Developer, Senior, Amtrust Bank • Newsletter Editor, North East Ohio Oracle Users Group • Has been working with Oracle since 1988 • Past Presenter at meetings of: • Independent Oracle Users Group • North East Ohio Oracle Users Group

  3. Agenda • Brief History • Review Join Technologies • Analysis • Recommendation

  4. ANSI/Oracle Support History • ANSI here refers to SQL/99 Join Syntax • The standard to which all RDBMS vendors strive to comply • SQL/99 support started with Oracle 9i in 2001 • Two years after the release of the standard, Oracle supports it. • This presentation restricted to the Oracle implementation of the ANSI standard

  5. 3 Join Condition Types • Equijoin • Columns with the same name • Columns with different names • Outerjoin • Left (left driving table) • Right (right driving table) • Full (both tables driving) • Cross/Cartesian product

  6. Traditional Equijoin - Same Name • Traditional Oracle Approach SELECT e.ename AS Employee_name, d.deptno, d.dname AS Department_name FROM emp e, dept d WHERE e.deptno = d.deptno; Table prefix is required to remove ambiguity on common columns Join conditions must be listed

  7. ANSI Equijoin Natural Syntax • ANSI SQL Natural Join SELECT ename AS employee_name, deptno, dname AS department_name FROM emp NATURAL JOIN dept; No table prefix if column is part of join condition. No commas between tables. Join columns implied, based on columns that have the same name God forbid that you accidentally add a non-join column to both tables…(um.. audit columns...)

  8. ANSI Equijoin Using Syntax • ANSI SQL Join USING SELECT d.dname, e.ename FROM emp d JOIN dept d USING ( deptno ); Table prefix allowed on columns that are not part of the using clause (join condition) Several columns share same name, only joining on some of them, in this case deptno Add additional join columns using ( deptno, join_col2, join_col3, …)

  9. Traditional Equijoin Syntax • Traditional Join, columns different SELECT d.department_name, l.city FROM departments d, locations l WHERE d.location_id = l.id; Join column names are different

  10. ANSI On Equijoin Syntax • ANSI SQL ON SELECT d.department_name, l.city FROM departments d JOIN locations l ON ( d.location_id = l.id ); Use ON when join column names are different List join conditions here like traditional syntax

  11. ANSI Equijoin Syntax • ANSI SQL Multi Table On SELECT e.empno, l.loc_id, d.dname, l.state_tx FROM locations l JOIN dept d ON ( d.location_id = l.id ) JOIN emp e ON ( d.deptno = e.deptno ); Bring in first table join No commas between tables Bring in second table join Any prior table column is visible – joins from left to right

  12. ANSI Equijoin Syntax • ANSI SQL INNER SELECT e.emp_id, l.city, d.dept_name, d.deptno FROM locations l INNER JOIN dept d ON ( d.location_id = l.id ) INNER JOIN emp e ON d.deptno = e.deptno; ON clause requires reference to join columns by table name to resolve ambiguity INNER – an optional keyword stating this is an equijoin (not an outer or cross join) Parenthesis are optional, we like to include them for clarity

  13. Traditional Outerjoin Syntax • Traditional Outer Join SELECT e.ename, d.dname FROM emp e, dept d WHERE e.deptno (+) = d.deptno NULL in name if no employees in the department. Traditional Outer Join Notation (+) indicator denotes expand records on this side if needed

  14. ANSI Outerjoin Syntax • Left Outer Join SELECT e.ename, d.dname FROM dept d LEFT OUTER JOIN emp e ON (e.deptno = d.deptno); NULL in last name if no employees in the department. OUTER keyword is optional. LEFT denotes that the dominant table is to the left (dept) and that all of it’s rows will be returned. The right table is expanded with NULL records

  15. ANSI Outerjoin Syntax • Left Outer Join SELECT e.ename, d.dname FROM dept d NATURAL LEFT JOIN emp e; USING e.g. LEFT JOIN emp e USING (deptno) can be used in an INNER and OUTER join. We don’t recommend using it here either! NATURAL can be used in an INNER and OUTER join.

  16. ANSI Outerjoin Syntax • Right Outer Join SELECT e.ename, d.dname FROM emp e RIGHT OUTER JOIN dept d ON (e.deptno = d.deptno); NULL in last name if no employees in the department. RIGHT OUTER denotes that the dominant table is to the right. The left table gets expanded with NULLS.

  17. Traditional Outerjoin Syntax -Close • Full Outer Join • Can only be represented with a “UNION” query. SELECT e.ename, d.dname FROM emp e, dept d WHERE e.deptno (+) = d.deptno UNION SELECT e.ename, d.dname FROM emp e, dept d WHERE e.deptno = d.deptno (+) Shouldn’t see many of these(We’ve never needed one) UNION ALL is incorrect as it results in duplicate rows UNION performs an implicit “DISTINCT” on result – possibly removing desired rows This “full” join syntax can be found on internet as “true” full join

  18. Traditional Full Close-Execution scott@VOTER> SELECT e.ename, 2 d.dname 3 FROM emp e, dept d 4 WHERE e.deptno (+) = d.deptno 5 UNION 6 SELECT e.ename, 7 d.dname 8 FROM emp e, dept d 9 WHERE e.deptno = d.deptno (+) 10 ; 16 rows selected. Execution Plan ---------------------------------------------------------- 0 SELECT STATEMENT Optimizer=ALL_ROWS (Cost=15 Card=28 Bytes=588) 1 0 SORT (UNIQUE) (Cost=15 Card=28 Bytes=588) 2 1 UNION-ALL 3 2 HASH JOIN (OUTER) (Cost=7 Card=14 Bytes=294) 4 3 TABLE ACCESS (FULL) OF 'DEPT' (TABLE) (Cost=3 Card=5 Bytes=60) 5 3 TABLE ACCESS (FULL) OF 'EMP' (TABLE) (Cost=3 Card=14 Bytes=126) 6 2 HASH JOIN (OUTER) (Cost=7 Card=14 Bytes=294) 7 6 TABLE ACCESS (FULL) OF 'EMP' (TABLE) (Cost=3 Card=14 Bytes=126) 8 6 TABLE ACCESS (FULL) OF 'DEPT' (TABLE) (Cost=3 Card=5 Bytes=60) Plan reflects the implicit DISTINCT inherent in UNION clause Notice Cost 15

  19. Traditional Full Join - True SELECT e.ename, d.dnameFROM emp e, dept dWHERE e.deptno = d.deptno(+)UNION ALLSELECTNULL, d.dnameFROM dept dWHERENOTEXISTS (SELECT 1 FROM emp e WHERE e.deptno = d.deptno) Outer join emp table with the dept table – all emp rows now returned Use UNION ALL to avoid implicit DISTINCT inherent in UNION Add Dept rows that have no match from emp This syntax can be found on internet at http://optimizermagic.blogspot.com under post on “Outerjoins in Oracle”

  20. Traditional Full Join True-Execution scott@VOTER> SELECT e.ename, d.dname 2 FROM emp e, dept d 3 WHERE e.deptno = d.deptno(+) 4 UNION ALL 5 SELECT NULL, d.dname 6 FROM dept d 7 WHERE NOT EXISTS 8 (SELECT 1 9 FROM emp e 10 WHERE e.deptno = d.deptno); 16 rows selected. Execution Plan ---------------------------------------------------------- 0 SELECT STATEMENT Optimizer=ALL_ROWS (Cost=13 Card=16 Bytes=324) 1 0 UNION-ALL 2 1 HASH JOIN (OUTER) (Cost=7 Card=14 Bytes=294) 3 2 TABLE ACCESS (FULL) OF 'EMP' (TABLE) (Cost=3 Card=14 Bytes=126) 4 2 TABLE ACCESS (FULL) OF 'DEPT' (TABLE) (Cost=3 Card=5 Bytes=60) 5 1 HASH JOIN (ANTI) (Cost=7 Card=2 Bytes=30) 6 5 TABLE ACCESS (FULL) OF 'DEPT' (TABLE) (Cost=3 Card=5 Bytes=60) 7 5 TABLE ACCESS (FULL) OF 'EMP' (TABLE) (Cost=3 Card=14 Bytes=42) Explain plan for “True” traditional outer join – SORT (UNIQUE) missing Cost 13 here, prior plan had cost of 15

  21. ANSI Outerjoin Syntax • Full Outer Join SELECT e.ename, d.dname FROM emp e FULL OUTER JOIN dept d ON (e.deptno = d.deptno); NULL in last name if no employees in the department. NULL in department name if employee not in a department. OUTER is optional FULL OUTER denotes that the table to the right AND the table to the left will have all their records returned

  22. ANSI Full Execution Plan scott@VOTER> SELECT e.ename, 2 d.dname 3 FROM emp e 4 FULL OUTER JOIN dept d 5 ON (e.deptno = d.deptno); 16 rows selected. Execution Plan ---------------------------------------------------------- 0 SELECT STATEMENT Optimizer=ALL_ROWS (Cost=13 Card=16 Bytes=256) 1 0 VIEW (Cost=13 Card=16 Bytes=256) 2 1 UNION-ALL 3 2 HASH JOIN (OUTER) (Cost=7 Card=14 Bytes=294) 4 3 TABLE ACCESS (FULL) OF 'EMP' (TABLE) (Cost=3 Card=14 Bytes=126) 5 3 TABLE ACCESS (FULL) OF 'DEPT' (TABLE) (Cost=3 Card=5 Bytes=60) 6 2 HASH JOIN (ANTI) (Cost=7 Card=2 Bytes=30) 7 6 TABLE ACCESS (FULL) OF 'DEPT' (TABLE) (Cost=3 Card=5 Bytes=60) 8 6 TABLE ACCESS (FULL) OF 'EMP' (TABLE) (Cost=3 Card=14 Bytes=42) Cost 13 = Cost of Traditional True

  23. Traditional Cross Join/Cross Product • Cross Join SELECT emp_id, ename, dname FROM emp e, dept d WHERE d.deptno = 10; Inadvertent cross join not obvious if joined table has a single row No join condition between tables… um, normally not good.

  24. ANSI Cross Join/Cross Product • Cross Join SELECT emp_id, ename, dname FROM emp e CROSS JOIN dept d WHERE d.deptno = 10; Explicit CROSS condition, impossible to do this accidentally.

  25. ANSI Correlated Join • Correlated Query Syntax Join SELECT empno, ename FROM emp e WHERE EXISTS ( SELECT NULL FROM dept d INNER JOIN locations l ON ( l.loc_id = d.loc ) WHERE d.deptno = e.deptno ); ANSI doesn’t allow join clause on first table Only tables in “current” FROM clause visible to ANSI join logic Not really a “mixed” syntax join

  26. ANSI Correlated Subquery Issues SELECT * FROM dept d INNER JOIN locations2 l USING ( loc ) WHERE EXISTS ( SELECT NULL FROM emp e WHERE e.loc = l.loc ) ORA-25154: column part of USING clause cannot have qualifier “NATURAL” joins have the same issue Don’t be tempted to remove the table prefix “l” Scope of reference dictates that the closest column be used

  27. ANSI Outer Join Subtleties SELECT d.deptno, e.ename, e.job  FROM dept d        LEFT JOIN emp e         ON (    e.deptno = d.deptno             AND e.job = 'SALESMAN'); DEPTNO ENAME JOB ====== ====== ======== 30    ALLEN    SALESMAN30    WARD    SALESMAN 30    MARTIN   SALESMAN30    TURNER   SALESMAN50        40        20        10  Filter is applied before join is executed A number of rows returned that have “OUTER” joined emp data Only dept 30, Sales, has SALESMAN as a job.

  28. ANSI Outer Join Subtleties SELECT d.deptno, e.ename, e.job  FROM dept d        LEFT JOIN emp e         ON (    e.deptno = d.deptno) WHERE e.job = 'SALESMAN'; DEPTNO ENAME JOB ====== ====== ======== 30    ALLEN    SALESMAN30    WARD     SALESMAN30    MARTIN   SALESMAN30    TURNER   SALESMAN Filter is applied after join is executed No outer joined data The condition has effectively converted this OUTER JOIN query to an INNER JOIN

  29. Mixed Traditional/ANSI Join • Mixed Syntax Join SELECT emp_id, ename, dname FROM emp e INNER JOIN dept d USING (deptno), dual WHERE deptno = 10; Presentation Bonus – This section not in conference proceedings. Oracle will run this without throwing an error Uhg…. Choose one or the other, but not both please!

  30. Mixed Syntax Join scott@VOTER> SELECT empno, 2 ename, 3 dname, 4 dummy 5 FROM dual, 6 emp e 7 INNER JOIN dept d ON (d.deptno = e.deptno) 8 WHERE e.deptno = 10; EMPNO ENAME DNAME D ---------- ---------- -------------- - 7782 CLARK ACCOUNTING X 7839 KING ACCOUNTING X 7934 MILLER ACCOUNTING X 3 rows selected. Oracle will run this without throwing an error Multiple traditional and ANSI sections are allowed

  31. Mixed Syntax Join scott@VOTER> SELECT empno, 2 ename, 3 dname, 4 dummy 5 FROM emp e 6 dual, 7 INNER JOIN dept d 8 ON ( d.deptno = e.deptno ) 9 WHERE e.deptno = 10; dual, * ERROR at line 6: ORA-00933: SQL command not properly ended Traditional mixed in between ANSI

  32. Mixed Syntax Join SELECT empno, ename, dname, dummy FROM dual, emp eINNERJOIN dept d on d.deptno = e.deptno and dummy ISNOTNULLWHERE e.deptno = 10; and dummy IS NOT NULL * ERROR at line 8: ORA-00904: "DUMMY": invalid identifier Presence of both comma (Traditional) and JOIN Mixed syntax join ANSI joins can only see other tables taking part in ANSI join

  33. ANSI vs Traditional Join Analysis • Impact areas • Code Clarity • Readability • Join Errors • Flexibility • Ease of Use • Developer Training • DBA Training • Legacy Code • Standards

  34. Code Clarity – Readability (Traditional) SELECT /*+ qb_name(orig) */ fdla.dim_borrower_v_id dim_borrower_v_id FROM dim_as_of_date_vw daod, dim_daily_loan_applctn_detl ddlad, dim_disbursement_date_vw dddv, dim_loan_originator dlo, fact_daily_loan_application fdla, dim_loan_applctn_status_vw dlasv WHERE daod.dim_as_of_date_v_id = ddlad.dim_as_of_date_v_id AND daod.dim_as_of_date_v_id = fdla.dim_as_of_date_v_id AND ddlad.dim_daily_loan_applctn_detl_id =fdla.dim_daily_loan_applctn_detl_id AND ddlad.dim_as_of_date_v_id = fdla.dim_as_of_date_v_id AND dddv.dim_disbursement_date_v_id = fdla.dim_disbursement_date_v_id AND dlo.dim_loan_originator_id = fdla.dim_loan_originator_id AND dlasv.DIM_LOAN_APPLCTN_STATUS_V_ID = fdla.DIM_LOAN_APPLCTN_STATUS_V_ID AND NOT (dlasv.STATUS_CODE BETWEEN '700' AND '740') AND NOT (dlasv.status_code BETWEEN '000' AND '429') AND daod.as_of_calendar_date = (CASE WHEN &in_DATE_SLICE IS NULL THEN LAST_DAY (ADD_MONTHS (TRUNC(SYSDATE), -1)) + &c_DEFAULT_SLICE_OFFESET ELSE TO_DATE( &in_DATE_SLICE, &c_DATE_FORMAT ) END) AND dddv.disburse_date BETWEEN TRUNC(NVL(TO_DATE(&in_START_REPORT_MONTH,&c_DATE_FORMAT),ADD_MONTHS(SYSDATE, -1)), 'MM') AND TRUNC (LAST_DAY (NVL(TO_DATE(&in_END_REPORT_MONTH,&c_DATE_FORMAT),ADD_MONTHS(SYSDATE, -1)))) AND ddlad.loan_transfer_status_code != 'T' Can you quickly determine how tables are joined? This is a real join we’ve implemented as part of a recent project

  35. Code Clarity – Readability (ANSI) SELECT /*+ qb_name(orig) */ fdla.dim_borrower_v_id dim_borrower_v_id FROM dim_as_of_date_vw daod INNER JOIN fact_daily_loan_application fdla ON (daod.dim_as_of_date_v_id = fdla.dim_as_of_date_v_id) INNER JOIN dim_daily_loan_applctn_detl ddlad ON ( ddlad.dim_as_of_date_v_id = daod.dim_as_of_date_v_id AND ddlad.dim_daily_loan_applctn_detl_id = fdla.dim_daily_loan_applctn_detl_id AND ddlad.dim_as_of_date_v_id = fdla.dim_as_of_date_v_id ) INNER JOIN dim_disbursement_date_vw dddv ON ( dddv.dim_disbursement_date_v_id = fdla.dim_disbursement_date_v_id) INNER JOIN dim_loan_originator dlo ON (dlo.dim_loan_originator_id = fdla.dim_loan_originator_id) INNER JOIN dim_loan_applctn_status_vw dlasv ON (dlasv.dim_loan_applctn_status_v_id = fdla.dim_loan_applctn_status_v_id) WHERE NOT (dlasv.STATUS_CODE BETWEEN '700' AND '740') AND NOT (dlasv.status_code BETWEEN '000' AND '429') AND daod.as_of_calendar_date = (CASE WHEN &in_DATE_SLICE IS NULL THEN LAST_DAY (ADD_MONTHS (TRUNC(SYSDATE), -1)) + &c_DEFAULT_SLICE_OFFESET ELSE TO_DATE( &in_DATE_SLICE, &c_DATE_FORMAT ) END) AND dddv.disburse_date BETWEEN TRUNC(NVL(TO_DATE(&in_START_REPORT_MONTH,&c_DATE_FORMAT),ADD_MONTHS(SYSDATE, -1)), 'MM') AND TRUNC (LAST_DAY (NVL(TO_DATE(&in_END_REPORT_MONTH,&c_DATE_FORMAT),ADD_MONTHS(SYSDATE, -1)))) AND ddlad.loan_transfer_status_code != 'T' Table Join Conditions Are Easily Identified

  36. Code Clarity – Join Errors • Traditional Syntax SELECT col1, col2, ... FROM tab1 t1, tab2 t2, ... WHERE ... Is a table join condition missing? How do you know?

  37. Code Clarity – Join Errors • ANSI Syntax SELECT col1, col2, ... FROM tab1 t1 [join type] tab2 t2 [join condition] ... WHERE ... must identify join type: INNER OUTER FULL CROSS “Impossible” to do inadvertent CROSS join Identifies join condition USING or ON

  38. Flexibility – (+) Restrictions not present in ANSI • You cannot specify the (+) operator in a query block that also contains FROM clause join syntax. • The (+) operator can appear only in the WHERE clause or, in the context of left-correlation (that is, when specifying the TABLE clause) in the FROM clause, and can be applied only to a column of a table or view. • If A and B are joined by multiple join conditions, then you must use the (+) operator in all of these conditions. If you do not, then Oracle Database will return only the rows resulting from a simple join, but without a warning or error to advise you that you do not have the results of an outer join. • The (+) operator does not produce an outer join if you specify one table in the outer query and the other table in an inner query. • You cannot use the (+) operator to outer-join a table to itself, although self joins are valid. For example, the following statement is not valid: SELECT employee_id, manager_id FROM employees WHERE employees.manager_id(+) = employees.employee_id; • However, the following self join is valid: SELECT e1.employee_id, e1.manager_id, e2.employee_id FROM employees e1, employees e2 WHERE e1.manager_id(+) = e2.employee_id; • The (+) operator can be applied only to a column, not to an arbitrary expression. However, an arbitrary expression can contain one or more columns marked with the (+) operator. • A WHERE condition containing the (+) operator cannot be combined with another condition using the OR logical operator. • A WHERE condition cannot use the IN comparison condition to compare a column marked with the (+) operator with an expression. • A WHERE condition cannot compare any column marked with the (+) operator with a subquery. “Oracle strongly recommends that you use the more flexible FROM clause (ANSI) join syntax”

  39. Ease of Use/Developer & DBA Training • Traditional Join • Long time Oracle developers do nothing • New Oracle Developers need to learn Oracle syntax • ANSI Join • Works with SQL Server/Oracle/MySQL/… • Syntax is more readable/self documenting • Natural join is “un-natural” - can lead to errors

  40. Installed Code Base • ANSI Joins not present in the Oracle installed code base • ANSI Joins present in other RDBMS installed code • More of these databases coming all the time • Harm in having two join syntaxes • Support personnel have to be comfortable with both syntaxes • Additional training required

  41. Fishbone Diagram Only Allow Traditional Join Syntax Only Support One Coding Style Installed Oracle Code Base No Natural Join Possibility Error FreeSQL Multi-Vendor RDBMS Support Code Clarity Fewer Join Condition Errors Standards Based Feature Rich Allow ANSI Join Syntax

  42. Recommendations • Allow both • Provide training so that all are familiar with both • Place some restrictions on ANSI syntax to prevent problems • Do not allow NATURAL joins and possibly USING clause • Single SQL statements should use one or the other but not both • New development should try to use same syntax throughout • Long term goal, ANSI only

  43. Session Goals • Familiarity with ANSI Join Syntax • Understanding the merits of the ANSI join syntax • Intention to start using the ANSI syntax

  44. ? Questions

  45. Thank You • Please complete the evaluation forms • My Name: Rumpi Gravenstein • Session Title: To ANSI or not to ANSI • Session #: 420 • If you have additional questions, I can be reached at rgravenstein@amtrust.com

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