Tables and Volatile Tables

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1 Derived Tables and Volatile Tables After completing this module, you will be able to: Use permanent tables for ad-hoc queries. Use both forms of Derived table syntax. Recognize variations for each form of derived table. Create volatile tables for session use. Distinguish between various ad-hoc strategies. Identify volatile table limitations. Distinguish between the two ON COMMIT options. Use volatile tables within views and macros. Teradata Corporation Copyright All Rights Reserved.

2 Permanent Tables for Ad Hoc Queries Reasons for interim use of permanent tables? To allow SQL to perform operations that: May not be possible from a normalized table May require multiple SQL statements For denormalizations such as: Summary tables Repeating groups For intermediate results which will be needed: Frequently, or On an on-going basis CREATE TABLE Daily_Net_Trans (Account_Number INTEGER,Total_Trans_Amount DECIMAL(14,2)) UNIQUE PRIMARY INDEX (Account_Number); INSERT INTO Daily_Net_Trans SELECT Account_Number, SUM(Trans_Amount) FROM Trans GROUP BY Account_Number; SELECT * FROM Daily_Net_Trans WHERE Account_Number IN ( , , );

3 Pros and Cons for Ad Hoc Perm Tables Pros about this strategy. Simpler SQL Doesn t have to continually reproduce aggregate results. PI choice of table may facilitate subsequent SQL. Open for use by multiple sessions if needed. Space survives a restart. Subsequent updates, inserts, and deletes can be performed on the rows of the table. Cons about this strategy. Separate steps to create and populate table. Requires extra perm space for temp table. Table may need to be dropped when no longer needed. If not, then extra maintenance may be required. Data Dictionary access is necessary for creating and dropping

4 Temporary Table Choices Views (Taught in Introduction to SQL and known to students of this course) Local to a query Uses Spool Derived Tables (Taught in Introduction To SQL and known to students of this course) Local to the query Incorporated into SQL query syntax Discarded when query finishes No Data Dictionary involvement Volatile Tables (This course) Local to a session Uses CREATE VOLATILE TABLE syntax Discarded automatically at session end No Data Dictionary involvement Global Temporary Tables (This course) Local to a session Uses CREATE GLOBAL TEMPORARY TABLE syntax Materialized instance of table discarded at session end Creates and keeps table definition in Data Dictionary This Module

5 Derived Tables Derived tables: are ANSI standard. are database created tables that are used for a single query only. are discarded by the database when they are no longer required. are materialized into spool. are referenced and treated as a real table. must be defined by the author of the query, and require - a table name columns and their names a SELECT that is used to populate the table More common form: SELECT Last_Name, Salary_Amount, AvgSal FROM Employee e, (SELECT AVG(Salary_Amount) FROM Employee) AS AvgT (AvgSal) WHERE e.salary_amount > AvgT.AvgSal; Query to populate AvgT Table Name AvgT Column Name(s) AvgSal

6 Another Derived Table Syntax Form More common usage? SELECT Last_Name, Salary_Amount, AvgSal FROM Employee e, (SELECT AVG(Salary_Amount) FROM Employee) AS AvgT (AvgSal) WHERE e.salary_amount > AvgT.AvgSal; Query to populate AvgT Table Name AvgT Column Name(s) AvgSal Column Name(s) AvgSal Table Name AvgT Query to populate AvgT The SELECT (projection) appears after the derived table definition. WITH Form WITH AvgT (AvgSal) AS (SELECT AVG(Salary_Amount) FROM Employee) SELECT Last_Name, Salary_Amount, AvgSal FROM AvgT t, Employee e WHERE e.salary_amount > t.avgsal;

7 Derived Tables and Joins SELECT e.department_number, e.last_name, e.salary_amount, t.avgsal FROM Employee e JOIN (SELECT Department_Number AS Dept#, AVG(Salary_Amount) AS AvgSal FROM Employee GROUP BY 1) AS t ON e.department_number = t.dept# WHERE e.salary_amount > t.avgsal ORDER BY 1; WITH t (dept#, AvgSal) AS (SELECT Department_Number, AVG(Salary_Amount) FROM Employee GROUP BY 1) SELECT e.department_number, e.last_name, e.salary_amount, t.avgsal FROM Employee e JOIN t ON e.department_number = t.dept# WHERE e.salary_amount > t.avgsal ORDER BY 1; department_number last_name salary_amount AvgSal Morrissey Kubic Daly Brown Villegas Charles Wilson Ratzlaff Runyon

8 CREATE TABLE AS and Derived Tables CREATE MULTISET TABLE dlm.mindeptsal AS ( WITH Temp (Dept#, AvgSal) AS (SELECT Department_Number, AVG(Salary_Amount) FROM Employee GROUP BY 1) SELECT d1.department_name AS DeptName, e1.last_name AS LastName, e1.salary_amount AS Salary, temp.avgsal AS DeptAvg FROM Employee AS e1, Department AS d1, Temp WHERE e1.department_number = d1.department_number AND AND e1.department_number = Temp.Dept# Temp.AvgSal IN (SELECT MIN(AvgSal) FROM Temp) ) WITH DATA PRIMARY INDEX (LastName); Create a permanent table having the last name, department name, salary and average department salary for each employee in the department with the smallest average salary. Note the data type DeptName LastName Salary DeptAvg research and development Stein E 004 research and development Kanieski E 004 research and development Kubic? E 004

9 Volatile Table Syntax CREATE VOLATILE TABLE vt_deptsal (deptno SMALLINT,avgsal DEC(9,2),maxsal DEC(9,2),minsal DEC(9,2),sumsal DEC(9,2),empcnt SMALLINT); SHOW TABLE vt_deptsal Volatile tables are not defined in ANSI LOG indicates that a transaction journal is maintained. This is the default. CREATE SET VOLATILE TABLE DLM.vt_deptsal, FALLBACK, CHECKSUM = DEFAULT, LOG ( deptno SMALLINT, avgsal DECIMAL(9,2), maxsal DECIMAL(9,2), minsal DECIMAL(9,2), sumsal DECIMAL(9,2), empcnt SMALLINT) PRIMARY INDEX ( deptno ) ON COMMIT DELETE ROWS; NO LOG allows for better performance. ON COMMIT DELETE ROWS indicates to delete all table rows after a commit (end transaction). This is the default. ON COMMIT PRESERVE ROWS indicates to keep table rows at TXN end.

10 Pros and Cons of Volatile Tables Pros about this construct. Simpler SQL Doesn t have to continually reproduce aggregate results. PI choice of table may facilitate subsequent SQL. Local (private) to a session (i.e. can not be viewed from other sessions). Subsequent updates, inserts, and deletes can be performed on the rows of the table. Table is automatically dropped at session end or manually by user. No dictionary access required. Cons about this construct. Separate steps to create and populate table. Requires extra spool space for temp table. No secondary indexes allowed. Statistics can not be collected. Holds on to spool longer.

11 Volatile Table Restrictions Up to 1000 volatile tables are allowed for a single session. At the time you create a volatile table, the name must be unique among all global and permanent object names in the database that has the name of the login user. CREATE VOLATILE TABLE username.table1 CREATE VOLATILE TABLE table1 CREATE VOLATILE TABLE databasename.table1 Username must be that of logon. Default must be that of logon. Can not use spool of another database or user. Each session can use the same VT name (local to session). VT name cannot duplicate existing object name for this user Perm or Temp table names View names Macro names Trigger names, etc. FALLBACK: Electable but not often useful for VTs. VTs don t survive a system reset. Options not permitted: Permanent Journaling Referential Integrity CHECK constraints Column compression Column default values Column titles Named indexes

12 HELP and SHOW (Volatile) TABLE CREATE VOLATILE TABLE vt_deptsal1 ( deptno SMALLINT, avgsal DECIMAL(9,2), maxsal DECIMAL(9,2), minsal DECIMAL(9,2), sumsal DECIMAL(9,2), empcnt SMALLINT ); SHOW TABLE vt_deptsal1; HELP VOLATILE TABLE; Table Name Table Id vt_deptsal1 30C0BC vt_deptsal2 30C0BD HELP DATABASE command does not show VT s. Create the volatile table. CREATE SET VOLATILE TABLE DLM.vt_deptsal1, FALLBACK, CHECKSUM = DEFAULT, LOG ( deptno SMALLINT, avgsal DECIMAL(9,2), maxsal DECIMAL(9,2), minsal DECIMAL(9,2), sumsal DECIMAL(9,2), empcnt SMALLINT) PRIMARY INDEX ( deptno ) ON COMMIT DELETE ROWS; DROP TABLE vt_deptsal1

13 ON COMMIT DELETE ROWS (Implicit Transactions) Create a volatile table. CREATE VOLATILE TABLE vt_deptsal (deptno SMALLINT,avgsal DEC(9,2),maxsal DEC(9,2),minsal DEC(9,2),sumsal DEC(9,2),empcnt SMALLINT); Populate the volatile table with computed aggregates. INSERT INTO vt_deptsal SELECT dept,avg(sal),max(sal),min(sal), SUM(sal), COUNT(emp) FROM emp GROUP BY 1; SELECT * FROM vt_deptsal ORDER BY 3; *** Query completed. No rows found. Remember: The default is ON COMMIT DELETE ROWS Rows are deleted immediately after the insert for implicit transactions!

14 ON COMMIT DELETE ROWS (Explicit Transactions) Create a volatile table. CREATE VOLATILE TABLE vt_deptsal (deptno SMALLINT,avgsal DEC(9,2),maxsal DEC(9,2),minsal DEC(9,2),sumsal DEC(9,2),empcnt SMALLINT); BT; INSERT INTO vt_deptsal (1, 2, 3, 4, 5, 6); SELECT * FROM vt_deptsal; deptno avgsal maxsal minsal sumsal empcnt ET; SELECT * FROM vt_deptsal; *** Query completed. No rows found. The default of ON COMMIT DELETE ROWS deleted the rows immediately after the ET; This would work the same for ANSI mode explicit transactions.

15 ON COMMIT PRESERVE ROWS Create a volatile table. CREATE VOLATILE TABLE vt_deptsal (deptno SMALLINT,avgsal DEC(9,2),maxsal DEC(9,2),minsal DEC(9,2),sumsal DEC(9,2),empcnt SMALLINT) ON COMMIT PRESERVE ROWS; BT; INSERT INTO vt_deptsal (1, 2, 3, 4, 5, 6); SELECT * FROM vt_deptsal; deptno avgsal maxsal minsal sumsal empcnt ET; SELECT * FROM vt_deptsal; deptno avgsal maxsal minsal sumsal empcnt

16 Limitations The following commands are not applicable to VT s: COLLECT/DROP/HELP STATISTICS CREATE/DROP INDEX ALTER TABLE GRANT/REVOKE privileges DELETE DATABASE/USER (does not drop VT s) VT s may not: Use ACCESS LOGGING. Be RENAMEd. Be loaded with MultiLoad or FastLoad utilities.

17 Volatile Tables from Derived Tables CREATE MULTISET VOLATILE TABLE VT_MinDeptSal AS ( WITH Temp (Dept#, AvgSal) AS (SELECT Department_Number, AVG(Salary_Amount) FROM Employee GROUP BY 1) SELECT d1.department_name AS DeptName, e1.last_name AS LastName, e1.salary_amount AS Salary, temp.avgsal AS DeptAvg FROM Employee AS e1, Department AS d1, Temp WHERE e1.department_number = d1.department_number AND AND e1.department_number = Temp.Dept# Temp.AvgSal IN (SELECT MIN(AvgSal) FROM Temp) ) WITH DATA PRIMARY INDEX (LastName) ON COMMIT PRESERVE ROWS; SELECT * FROM VT_MinDeptSal; Create a Volatile table having the employee name, department name and salary for each employee in the department with the smallest average salary. HELP VOLATILE TABLE; Table Name Table Id VT_MinDeptSal 10C0B DeptName LastName Salary DeptAvg customer support Rogers E 004 customer support Johnson E 004 customer support Trader E 004 customer support Phillips E 004 customer support Machado E 004 customer support Brown E 004 customer support Hoover E 004

18 Use with Views and Macros REPLACE MACRO vt1 AS (CREATE VOLATILE TABLE vt_deptsal3 (deptno SMALLINT,avgsal DEC(9,2),empcnt SMALLINT) 1 ON COMMIT PRESERVE ROWS; ); Since spool does not survive a restart, Volatile tables are more likely to be used in an ad hoc environment. This usage is more reflective of batch processing. EXEC vt1; 2 Table must be created before doing the following REPLACE MACRO vt2 3 AS (INSERT vt_deptsal3 SELECT Department_Number, AVG(Salary_Amount), COUNT(Salary_Amount) FROM EMPLOYEE GROUP BY 1;); REPLACE VIEW vt3 AS SELECT e.last_name, 4 v.deptno, e.salary_amount, v.avgsal FROM Employee e, vt_deptsal3 v WHERE e.department_number = v.deptno AND e.salary_amount > v.avgsal; Example of usage. EXEC vt1; *** Table has been created. EXEC vt2; *** Insert completed. 8 rows added. SELECT * FROM vt3 WHERE deptno = 401; last_name deptno salary_amount avgsal Brown Trader Rogers Johnson

19 Another View and Macro Strategy REPLACE MACRO vt1 1 AS (CREATE VOLATILE TABLE vt_deptsal3 AS (SELECT Department_Number AS deptno, AVG(Salary_Amount) AS avgsal, COUNT(Salary_Amount) AS salcnt FROM Employee GROUP BY 1) WITH DATA UNIQUE PRIMARY INDEX (deptno) ON COMMIT PRESERVE ROWS; ); Compare this sequence to the one on the previous page. EXEC vt1; 2 Table must be created before doing the following. REPLACE VIEW vt2 AS SELECT e.last_name, v.deptno, e.salary_amount (DEC(10,2)), v.avgsal (DEC(10,2)) FROM Employee e, vt_deptsal3 v WHERE e.department_number = v.deptno AND e.salary_amount > v.avgsal; 3 Example of usage. EXEC vt1; SELECT * FROM vt2 WHERE deptno = 401; last_name deptno salary_amount avgsal Brown Trader Johnson Rogers

20 Volatile Table Quiz In the following exercise, User A has two parallel sessions. Assuming the given sequence of events, which will succeed, which will fail, and why? User A CVT = Create Volatile Table CPT = Create Permanent Table Session 1 Session 2 Success/Failure/Reason CVT T1 CVT T1 SUCCESS SUCCESS CPT T2 SUCCESS CVT T2 FAILURE CVT T3 SUCCESS CPT T3 SUCCESS INSERT T3 SUCCESS (VT3) CVT T3 FAILURE INSERT T3 SUCCESS (PT3) DROP T3 SELECT * FROM T3 SUCCESS (VT3) SUCCESS (PT3)

21 Module 2: Summary There are two forms for writing derived tables: WITH and FROM. Views, Derived, Global and Volatile tables are all examples of temporary instance objects. Views, Derived tables and Volatile tables all use spool. ON COMMIT DELETE ROWS is the default for volatile tables. Volatile tables last until the end of the user s session logoff, when the database drops them automatically. Volatile tables are best suited for ad-hoc usage.

22 Module 2: Review Questions True or False: 1. You can define a volatile table with a unique primary index. True 2. The option ON COMMIT DELETE ROWS will result in the inserted rows being immediately deleted after the insert. False this is true only for implicit transactions. 3. You can not perform a SHOW TABLE on a derived table. True 4. You cannot qualify a volatile table create with a database name other than your user name. True 5. Volatile tables and derived tables use the same kind of space. True 6. You can create hundreds of derived tables for a single query. False True in TD13 7. You can drop a volatile table at anytime during your session. True

23 Module 2: Lab Exercise 1) Use the most compact method you can to create a volatile table based on the definition of the Department table and then populate it with data from the department table. Use the preserve option. Select all rows from the table you created. 2) Create another volatile table that averages the salary amounts for each department. Now issue a HELP command to verify the existence of the two volatile tables that you created. Do SHOW TABLE on one of them and then drop the first one and repeat the earlier HELP command. 3) Write a query using a derived table that lists employees that have salaries greater than average for their department. Contrast this with a query that does this referencing the table created in #2.

Tables From Existing Tables

Creating Tables From Existing Tables After completing this module, you will be able to: Create a clone of an existing table. Create a new table from many tables using a SQL SELECT. Define your own table