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单位：大连理工大学作者：陆坤，李凤岐，姜厚云

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大型主机平台系统应用开发基础 教育部－ IBM精品课程

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第九章 嵌入式数据库编程基础

9.1 大型机数据库对象介绍9.2 嵌入式 SQL 编程基础9.3 程序准备9.4 游标的使用9.5 动态 SQL 基础9.6 数据库的权限和锁的机制

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第一节大型主机数据库对象介绍

IBM 数据库历史主机数据库中的对象 ;创建存储组 , 数据库 , 表空间 , 表 , 试图 , 同

义词 , 别名索引等对象 ;数据在数据库中的存储方式；How to use SPUFI

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IBM DB2 发展史 四十年的理论研究应用产品， IBM 公司在数据库管理系统的研究和发展

中作出了巨大的贡献。 70 年代之前，层次型数据库占主导地位 (IBM IMS); 1970 年 ,IBM 研究中心 E.F. Codd 博士提出了关系数据库模型 , 紧接着 IBM 研

究中心发明了第一个关系数据库管理系统 SYSTEM R 和 SQL 语言 . 80 年代，基于 SQL 的关系数据库逐渐成为驻留， IBM 的关系数据库 DB2 住

在了大型机上的数据库应用。 1992 年 IBM 将 DB2 推向开放平台； 1997 年 IBM 发布 DB2 UDBV5 ，市场急剧扩大； 1999 年 IBM 发布 DB2V6 ，占据市场领导地位； 2000 年 IBM 发布 DB2V7.1— 电子商务数据库； 2001 年 IBM 发布 DB2V7.2— 电子商务数据库增强版； 2002 年 IBM 发布 DB2V8.1— 智能数据库； 2007 年 IBM 发布 DB2V9 — 第一个混合型数据库；

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IBM 引导信息管理走向新的高度

DUTIBM 在关系数据库技术领域的领导地位

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DB2 的先进性和广泛性 近 40 年关系数据库经验 超过 260 项数据库专利技术 Fortune 100, 100% 使用 DB2 Fortune 500,80% 使用 DB2 超过 1,000,000 张使用许可证 超过 60,000,000 最终用户 超过 450,000 公司使用 DB2 全世界 70 ％的企业数据存储在 DB2 中

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DB2: 增长最快的数据库

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DB2- 平台延伸最好的数据库 (1/3)

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DB2- 平台延伸最好的数据库 (2/3)

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DB2- 平台延伸最好的数据库 (3/3)

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DB2 Objects

DB2 Objects

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Sequence of defining objects

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Interfaces to define object

SQL Interfaces - Command line or file input interfaces

- SPUFI – SQL Processor Using File Input.( 重点） Tool on z/OS for entering SQL via file input

- QMF – Query Management Facility.

z/OS or workstation tool to allow interactive

SQL entry and processing.

- CLP – Command Line Processor.

It is used to dynamically execute SQL requests and/or DB2 commands.

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DB2 Naming Rules (1/2)

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DB2 Naming Rules(2/2)

DB and STG name must be unique in DB2 System All object names begin with A-Z,#,$;

following chars: A-Z,#,$,0-9; Name length: DB,TBS <= 8

others: <=128

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DB2 Storage Group

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Volumes

Are used in order Not dedicated to STG

Non-DB2 DS can be allocated on it One Can be assigned to different STG

MAX 133 volumes in a STG All volumes in a STG must the same type

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DB2 Database

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DB2 Database

CREATE DATABASE DB1

STOGROUP SG1 default STGBUFFERPOOL BP1 dflt table bp

INDEXBP BP2 dflt index bpCCSID UNICODE; dflt code

DSNDB04 is the default DB and is created when DB2 is installed.

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DB2 Table Space

What is a Table Space?DB2 storage StructureContains data rows for one or more tablesResides in a page set of one or more VSAM LDSCreated in a database using SQL

Three types of Table space:Simple Table SpaceSegmented Table SpacePartitioned Table Space

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Simple Table Space

Seldom used!

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Segmented Table Space

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SMPL and SEGMT Table Space

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Partitioned(Table-Controlled) Table Space

DUTTable-Controlled Partitioning Example(1/2)

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Table-Controlled Partitioning Example(2/2)

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Create Table-column attribute

DATABASE

TABLESPACE

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Default Attribute(1/2)

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Default Attribute(2/2)

DATA TYPE SYSTE DEFAULT

-------------------------------------------CHARACTER SPACES

NUMERIC 0s

VARCHAR ZERO LENGHTH

DATE CURRENT DATA

TIME CURRENT TIME

TIMESTAMP CURRENT TIMESTAMP

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CREATE TABLE- LIKE

•CHECK CONSTRAINS ARE NOT COPYED

•PR ,UNIQ,FK ARE NOT COPYED

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SYSTABLES Catalog Information

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Table Check Constraint Consideration

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-DISPLAY DATABASE Command

-DIS DB (DSNDB06)

,CHKP

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DB2 SYNONYM

Refer to a local table or view Refer to another owner’s tab or view as if it were yours. It can be thought of as a ‘private’ pointer to a table or view. A synonym can only be referenced by its owner

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DB2 SYNONYM - Example

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DB2 ALIAS

It is a pointer to a table or view It likes a virtual table It can be referenced by using a qualified name. The table or view could be located on a remote site.

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DB2 ALIAS - Example

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Naming Conversation for DS

DUTHow to use SPUFI （ SQL Processing Using File Input)

Environment Mainframe IP Address: 如： 218.25.163.36 DB2 subsystem: DB8G TSO USERID

• Each student has his own TSO Logon USERID. Use the USERID you are assigned to logon.

User datasets used in the practice – ST***.SPFUI.INPUT(SQL1)– ST***.SPFUI.OUTPUT

Note:

(1) These datasets are pre-created for each USER.

(2) Later we will see that these two datasets are used as SPUFI input and SPUFI output. And each user should use his own datasets. So when you take your practice, change *** to your USERID suffix.

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How to use SPFUI

Practice Steps (1) Connect to z/OS(2) Invoke DB2 panel(3) Set SSID parameter that tell SPUFI which DB2 subsystem

you’ll operate on. (4) Use SPUFI to manage DB2 data

• Set SPUFI Parameters • Define SQL input file to SPUFI• Define SQL output file to SPUFI• Enter edit panel and edit your queries ( you can have DDL, DML,DCL

here) • Run test queries through SPFUI and view results

(5) Use SPUFI to run your own queries(6) Summary

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How to use SPFUI

Invoke DB2 panel After you have enter ISPF. Type m.11.1 and type “enter key”, you will go to

DB2 panel.

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How to use SPFUI

Set target DB2 subsystem to SPUFI Picture shows the DB2 panel, choose “D”, the panel to set db2

subsystem will appear.

Current set DB2 subsystem that SPUFI will operate on

Form here, you can go to the panel which set DB2 subsystem that SPUFI will operate on

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How to use SPFUI

Set target DB2 subsystem to SPUFI (Continue) The picture below show how you set target DB2 subsystem. In our

testing environment it’s DB8G. Type DB8G and enter.

Type DB8G here to set the target DB2 subsystem as DB8G

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How to use SPUFI

Invoke SPUFI

Target DB2 subsystem: DB8G

Enter 1 to invoke SPUFI

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How to use SPUFI

Input/output datasets SPUFI uses datasets to hold it’s input/output. Before use, you must first

created these two datasets. In practice, please use “ST***.SPUFI.INPUT(SQL1)” and “ST***.SPUFI.OUT” which have been created

Input Dataset containing the SQL

Where the destination output will go

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Edit SQL You can edit the query from edit panel just like editing a normal

datasets. And you can also save all your changes

Run SQL • Edit panel F3Ctrl

How to use SPUFI

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View results After you run SPUFI, result page will appear as below picture Enter “F3” to go back to edit panel

How to use SPUFI

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Run your own queries Run your own DDL

• Sample: Create table test(c1 int, c2 int);

Run your own DML • Sample: insert into test values(1, 1);

• Sample: select * from test;

Run your own DCL • Grant select on test to public;

Summary

How to use SPUFI

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第二节 嵌入式编程基础

Using DelimitersUse Host variablesUse appropriate techniques to process

null dataSQLCA

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Delimiters(1/2)

Used by PRECOMPILER to identify SQL stmt to be translated

Must indicate beginning and end of each embedded SQL stmt

COBOL EXEC SQL SQL STMT END-EXEC.

C;C++;PL/1

EXEC SQL SQL STMT ;

Java #sql{ SQL STMT };

FORTRAN EXEC SQL SQL STMT

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SQL STMT in COBOL PROGRAMEXEC SQL

UPDATE TEMPL

SET WORKDEPT = ‘C02’ WHERE WORKDEPT = ‘C01’

END EXEC.

Notice: All COBOL delimiters and SQL statements must

begin at or after column 12.

SQL STMT in C or PL/I program EXEC SQL

UPDATE TEMPL

SET WORKDEPT = ‘C02’ WHERE WORKDEPT = ‘C01’ ;

In Java#sql { UPDATE TEMPL

SET WORKDEPT = ‘C02’ WHERE WORKDEPT = ‘C01’} ;

Delimiters(1/2)

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Host Variables

Host Variable is used to allow

setting a value before statement

is executed.

Host variable in SQL statement

preceded by a colon

Host variable must match column data type

Not usable for DB2 names ( Table name, column name,…)

NOTE: You can use any valid COBOL name for a host variable. Do not use host variable names that begin with ‘SQL’.

宿主变量是在程序和 DB2 之间传递数据的手段。

DUTHost Variables- insert a single row

SQL statement

INSERT INTO TEMPL (EMPNO, LASTNAME)

VALUES (‘000190’, ‘JONES’)

SQL statement in a program

EXEC SQL

INSERT INTO TEMPL (EMPNO, LASTNAME)

VALUES (:EMPNO, :NAME)

END-EXEC.

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SQL statement

UPDATE TEMPL

SET SALARY = SALARY * 1.05

WHERE JOBCODE = 54

SQL statement in a program

EXEC SQL

UPDATE TEMPL

SET SALARY = SALARY * :PERCENT

WHERE JOBCODE = :CODE

END-EXEC.

Host Variables - Update

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EXEC SQLSELECT LASTNAME, WORKDEPT

INTO :NAME, :DEPTNODEPTNOFROM TEMPLWHERE EMPNO = :EMPID

END-EXEC.

● Each column selected must have a corresponding host variable● The host variables are separated with commas.

Host Variables – To Receive a single row

DUTHost Variables - Specifying expressions in the SELECT

When you specify a list of items in the SELECT clause, you can use more than the column names of tables and views. You can request a set of column values mixed with host variable values and constants

Example 1MOVE 4476 TO RAISE.

MOVE ’000220’ TO PERSON.

EXEC SQL

SELECT WHERE EMPNO = :PERSON END-EXEC.

EMPNO, LASTNAME, SALARY, :RAISE, SALARY + :RAISE

INTO :EMP-NUM, :PERSON-NAME, :EMP-SAL, :EMP-RAISE, :EMP-TTL

FROM DSN8810.EMP

Example 2MOVE ’D11’ TO DEPTID.

EXEC SQL SELECT WORKDEPT, AVG(SALARY) INTO :WORK-DEPT, :AVG-SALARY FROM DSN8810.EMP

WHERE WORKDEPT = :DEPTID END-EXEC.

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Declaring Host Variables

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SQL type mapped to COBOL declarations(1/2)

DUTSQL type mapped to COBOL declarations(2/2)

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Declaration Considerations For COBOL

CREATE TABLE SIMPLE (TITLE CHAR(20) NOT NULL

NUMBER SMALLINT NOT NULL)

DATA DIVISION.

WORKING-STORAGE SECTION.EXEC SQL BEGAIN DECLARE SECTION END-EXEC.

01 IOAREA. 02 TITLE PIC X(20) 02 NUMBER S9(4) COMP.

EXEC SQL END DECLARE SECTION END-EXEC. PROCEDURE DIVISION.

EXEC SQLSELECT TITILE INTO:IOAREA.NUMBERFROM SIMPLE

WHERE NUMBER = :IOAREA.NUMBER

END-EXEC.

DUTDCLGEN-(Declarations Generator)

DUTDCLGEN-(Declarations DCLGEN-(Declarations

Generator)Generator)

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DCLGEN － example(1/2)

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DCLGEN － example(2/2)

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COBOL 程序中的 SQL INCLUDE 语句用于包含 DCLGEN声明。这样程序开发者就不用手工将 DCLGEN 自动生成的数据表或视图所对应的宿主变量结构写入 COBOL 源代码，而只需要将如下简单的语句写入 COBOL 源代码：

EXEC SQL

INCLUDE DEPT

END-EXEC.

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DCLGEN

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Host Structure Support in COBOL

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Host Structure Support in COBOL

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Processing Null Data

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Indicator Variables

INDICATOR VARIABLE(SMALLINT) is required if SELECTedcolumn allows null.

If column is NULL, INDICATOR VARIABLE is set to negative value (usually -1), VALUE VARIABLE is untouched. If column is NOT NULL, INDICATOR VARIABLE is set to positive value (usually 0).

INDICATOR VARIABLE can be set to negative value by program to indicate NULL on UPDATE or INSERT.

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Indicator Variable Example

主机变量和 indicator variable 之间没有分号

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Testing or Passing Null value

Tesing for NULL on SeletctEXEC SQL

SELECT JOBCODE,WORKDEPT,PHONENO

INTO:JC :JCI,:DPT,:PHO:PHOI

FROM TEMPL

WHERE EMPNO=:ID

END-EXEC.

IF JCI<0 MOVE “UNKN’ TO JC.

Passing NULL ValueIF(some condition) MOVE -1 TO PHOI

ELSE MOVE 0 TO PHOI.

EXEC SQL

UPDATE TEMPL

SET PHONENO=:PHONENO:PHI

WHERE EMPNO=:ID

END-EXEC.

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Indicator Variable Usage – Null Value

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SQLCA - SQL Communication Area

SQLCA ： SQL 通信区，在每个 SQL 语句或 DB2 命令执行的最后更新， DBA 使用 SQLCA 结构可将 SQL 语句执行的结果信息返回给应用程序。

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SQLCA 结构

01 SQLCA.05 SQLCAID PIC X(8).05 SQLCABC PIC S9(9) COMP.05 SQLCODE PIC S9(9) COMP.05 SQLERRM.

49 SQLERRML PIC S9(4) COMP.49 SQLERRMC PIC X(70).

05 SQLERRP PIC X(8)05 SQLERRD OCCURS 6 TIMES

PIC S9(9) COMP.05 SQLWARN

10 SQLWARN0 PIC X(1).10 SQLWARN1 PIC X(1).10 SQLWARN2 PIC X(1).……10 SQLWARN7 PIC X(1).

05 SQLEXT.10 SQLWARN8 PIC X(1).10 SQLWARN9 PIC X(1).10 SQLWARNA PIC X(1).10 SQLSTATE PIC X(5).

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SQLCA Codes

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Some Common SQLCODE Values

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SQLCA Warnings

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Coding Aids

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Coding Aids

WHENEVER Statement

- For exception handling Error message formatting routine

- CALL ‘DSNTIAR’ for COBOL on z/OS

- CALL DSNTIAR for PL/I on z/OS INCLUDE statement and INCLUDE files

- To add SQLCA structures to program and to provide function prototypes

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WHENEVER Statement

WHENEVER 语句：出错捕获语句，根据 SQL 语句返回的SQLCODE 决定是继续执行还是转向出错处理例程。其格式为：EXEC SQL WHENEVER Condition Action;

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WHENEVER Statement

Condition:- SQLERROR

● Negative SQLCODE- SQLWARNING

● Positive SQLCODE (not +100) ● Or SQLWARN0=‘W’

- NOT FOUND ● SQLCODE=+100

Action:- GO TO :X

● Control transferred to statement labeled X- CONTINUE

● Program continues with next statement ● Used to cancel effect of prior WHENEVER

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WHENEVER Statement Example

EXEC SQL WHENEVER NOTFOUND

GOTO :PROG-END.

……

EXEC SQL

SELECT COL1 FROM TB1 WHERE

COL2=‘C1’

END-EXEC.……

PROG-END.

EXIT.

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Error Message Formatting Routine

In z/OS, there is an Error Message Formatting Routine - DSNTIAR.

Format: CALL ‘DSNTIAR’ USING sqlca message lrecl

DSNTIAR takes error message from the SQLCA, formats it into a more readable form, and places the result in a message output area that you provide in your application program.

DUTAlternative to WHENEVER - COBOL Program

/*DECLARES FOR DSNTIAR*/01 ERROR-MESSAGE.

02 MESSAGE-LENGTH PIC S9(4) COMP VALUE +960.02 DETAIL-MESSAGE PIC X(120) OCCURS 8 TIMES.

01 LINE-LENGTH PIC S9(9) COMP VALUE +120.

SQL StatementIF SQLCODE < 0

CALL ‘DSNTIAR’ USING SQLCA ERROR-MESSAGE LINE-LENGTH.IF RETURN-CODE < 5

MOVE DETAIL-MESSAGE(1) TO DISPLAY-MESSAGE.MOVE DETAIL-MESSAGE(2) TO DISPLAY-MESSAGE.MOVE DETAIL-MESSAGE(3) TO DISPLAY-MESSAGE.

……

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SQL INCLUDE Statement

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第三节 程序准备

Understand the whole process to Understand the whole process to program a DB2 applicationprogram a DB2 application

Understand package and planUnderstand package and planUnderstand rebind strategyUnderstand rebind strategy

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Programming process

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Programming process

Compile/Link-edit

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Programming process

在嵌入式的 SQL 编程中，源程序包含应用代码和 SQL 语句。

程序在相关的源代码语言编译器编译之前，嵌入的 EXEC SQL 语句必须首先替换掉，替换成源代码的一些 CALL 调用语句。

这种用程序库调用来替换 SQL 语句的过程，由 DB2 的一个进程来完成，称为预编译器。

对于静态的嵌入式 SQL 程序， SQL 语句会由 DB2 的 bind过程来进行处理，生成 package

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Programming process

Normally a DB2 application has to go through 4 steps to complete an execution: Precompile Compile/Link-edit Bind Run (Execution)

During the process, below source are accessed or generated: Source code modules with embedded SQL Source code modules with DB2 APIs DBRM(bind files) Collection and Package Plan

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Precompile

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Precompile

Precompile

DB2 precompiler takes the application source code as input, and generates two outputs: modified code and DBRM

Precompiler comments out the SQL statements in the source code and replace them by language-specific calls.

From all the SQL statements it encounters, the precompiler constructs a DBRM, which then becomes the input of the Bind component.

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Precompile

Precompile

预编译器在处理的时候，并不访问 DB2

预编译器会验证 SQL 语法，还会为每个 SQL 产生一个一致性令牌和语句号。

预编译器会将 EXEC SQL INCLUDE 语句要引入的文件都 included进来。

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DBRM

DBRM

－ One DBRM corresponds to exactly one source module

－ contains extracted, parsed SQL source;

－ Is stored as a member in a partitioned dataset;

－ one member or file created per precompile;

－ will become input to BIND.

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Compile/Link-edit

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Compile/Link-edit

Compile/Link-edit

After compilation, the modified source code is compiled using the corresponding language-specific compiler into object module

The generated object module is linked with other (possible) object module to generate a load module for the whole application.

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Compile/Link-edit

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Bind

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Bind

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BIND

Bind package “Bind” a given DBRM to produce a package

When the bind file or DBRM is bound to the database, a package is created in the database. This package contains instructions about how to execute the SQL statements that were included in the source code.

A DBRM can be thought of as a “SQL source module”,while the package can be thought of the corresponding “object module”.

Bind Plan ： “Bind together” a list of packages(and/or a list of DBRMs) to produce

a plan.

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BIND

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BIND

Validation checks on the existence of necessary DB2 objects, for example, tables, views, and so forth.

With the resolution of table names, DB2 implicitly appends an unqualified table name with its owner’s ID.

Authority checking is performed to make sure that the BINDer or owner has the authority to create a program to access the data as required.

Access path selection consists of evaluating a number of different access paths and calculating their costs. The cheapest one will be retained.

The executable access code is stored in the directory, and the source SQL statements are stored in the DB2 catalog.

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RUN

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Bind- package and plan

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Bind process

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Bind process

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Bind

- BIND PACKAGE(collection-id) MEMBER(dbrm-member).

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Collection ID

Package are qualified with a collection. Package Name = Collection_Id.Package_Id

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Plans

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Package List A package list is a list of reference to individual packages

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Package and Plan

In between the load module and the packages, there is a need for an additional structure that will "guide" DB2 in its search for the appropriate package. This structure is called a "PLAN",

A PLAN contains a “PACKAGE LIST”, a list of pointers to packages

A package can only be located and executed via a PLAN

The dbrm name and the timestamp provided with the call is used to LOCATE the correct package via the package list

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Overview with packages

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第四节 游标的使用 Use DECLARE, OPEN, FETCH, and CLOSE Use DECLARE, OPEN, FETCH, and CLOSE

CURSOR statements to handles select CURSOR statements to handles select criteria that may return multiple rows in criteria that may return multiple rows in application programs.application programs.

Issue positioned UPDATE and DELETE Issue positioned UPDATE and DELETE statements (Know how to update and delete statements (Know how to update and delete rows with a cursor)rows with a cursor)

Multi-Row Fetch Host Variable Arrays

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Processing Result Set

仅返回一行的 SELECT 语句的结果的处理？ 通过 INTO 将结果放到宿主变量

多行呢？ 按上述方法：第一行放置在 INTO 字句定义地宿主变量中，同时

SQLCODE 被置为－ 811

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Processing Multiple Rows

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Sequential File Read

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Sequential File Read

1.Define file access

2.Open the file for reading

3.Read the first record

4.Read the next record

5.close the file

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Select with FETCH - COBOL

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CURSOR

DECLARE: 定义游标；游标名称和这个游标对应的 SQL 语句。DECLARE 语句不执行 SQL 语句，仅定义。

OPEN ：为检索列而准备好游标；打开游标，则执行相应的 SQL ，建立结果表。

FETCH: 从结果表中取数据，一次一行，并且给指定的宿主变量赋值。（一直 loop 到 SQLCODE=100 ）

CLOSE ：释放游标使用的所有资源。

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Select with FETCH － C or PL/I

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DELETE Via a Cursor － COBOL

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UPDATE Via a Cursor - COBOL

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U – Lock Usage

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Without FOR UPDATE OF

Terminal 1 issues the open cursor and fetches the first row. Receives an IS lock on the table, an S lock on the row.

Terminal 2 issues the open cursor and fetches the first row. Receives an IS lock on the table, an S lock on the row.

Terminal 1 tries to update the row it is reading. It gets an IX lock on the table through lock conversion. It needs to get an X lock on the row. It cannot get an X lock on the row since terminal 2 holds an S lock on the row. So, terminal 1 waits.

Terminal 2 decides to update the row it is reading. It gets an IX lock on the table through lock conversion. It needs to get an X lock on the row. It cannot get an X lock on the row since terminal 1 holds an S lock on the row. This is a 'deadlock'.

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With FOR UPDATE OF

Terminal 1 issues the open cursor and fetches the first row. Receives an IX lock on the table, an U-lock on the row.

Terminal 2 issues the open cursor and fetches the first row. Receives an IX lock on the table, but waits for a U-lock on the row.

Terminal 1 updates the row it is reading. It upgrades its lock to an X lock on the row.

Terminal 2 will wait until terminal 1 commits or it times out. Getting the U-locks may limit concurrency, but in this case, it prevented a deadlock.

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Update/Delete Via a Cursor

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Optimizer for n ROWs

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Fetch first k Rows only

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Cursor Manipulation

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Cursor Manipulation

CLOSE CURSOR releases the cursor, and addressability to the buffer is lost.

If a cursor is to be reused, it must be CLOSED before it is OPENED.

COMMIT will CLOSE any CURSOR that has not been defined WITH HOLD. (See the next visual.)

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WITH HOLD Cursor

即使 commit, 游标仍持有

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Cursor Repositioning

REQUIRMENT: UPDATE of a large number of rows, using a CURSOR. To avoid accumulating an excessive number of ROW LOCKS, issue a COMMIT after every 500 UPDATES.

CONSIDER: If restart capabilities must be included in the program, position of the cursor must be reestablished.

SULUTION: After ABEND ， reestablish position based upon a saved column value.

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Cursor repositioning – COBOL (1/2)

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Cursor repositioning – COBOL (2/2)

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Scrollable Cursors

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Scrollable Cursors

静态游标和动态游标的区别：

静态游标打开后，结果集的大小不变，结果集中行的数据顺序也不变。

动态游标打开后，结果集的大小可变，结果集中行的数据顺序也可变，即其他游标可以对结果集中进行插入，更新或删除操作。

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How to Scroll within the Result Table

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How to Scroll within the Result Table

The RELATIVE keyword is used to position the cursor relative to the current position.

ABSOLUTE keyword is used to position the cursor relative to the top or bottom of the result table

FETCH PRIOR, FETCH NEXT,FETCH FIRST, FETCH LAST

An example of the full syntax is as follows:

FETCH SENSITIVE RELATIVE 3 FROM C1 INTO :hv1, :hv2

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Scrollable Cursors

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How to Declare a Scrollable Cursor

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Insensitive Scrollable Cursors

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Sensitive Scrollable Cursors

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Sensitive and Insensitive

敏感和不敏感游标的区别：

不敏感的游标意味着在游标打开后，不能看到其他应用对基础表中的更改( 包括数据插入，更新和删除) ，不敏感的游标是只读的，结果表中行的数量和内容在游标打开的整个过程中不变。不敏感的游标不能用于数据更新和删除。

敏感的游标意味着在游标打开后，能够看到其他应用对基础表所作的更改，结果表中行的数量( 其他应用插入或删除) 在游标打开的整个过程中不变，但是行的内容可变 。敏感的游标能够用于数据更新和删除。

DUTFetch sensitive request which creates an Update Hole

DUTWhat happens when a FETCH request encounters a Hole in the Result Table?

DUTDynamic Scrollable Cursors – New in V8

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New in V8 -Dynamic Scrollable Cursors

Dynamic scrollable cursor allow for base table access instead of having to use a declared global temporary table .

Each FETCH shows the most current activity and is sensitive to all INSERTs,UPDATEs, and DELETEs:no more delete holes and missing updates-- allows visibility of updates and inserts done by you or other users

DECLARE DyCur SENSITIVE DYNAMIC SCROLL CURSOR FOR

SELECT TCID,NAME FROM TEST_CENTER;

DECLARE DyCur SENSITIVE DYNAMIC SCROLL CURSOR FOR

SELECT TCID,NAME FROM TEST_CENTER;

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Cursors Type comparision

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各游标定义和取数据时各不同参数的区别总结

DECLARE CURSOR 时使用的参数

FETCH 时使用的参数

注释 对基础表更改的敏感性

INSENSITIVE INSENSITIVE FETCH 缺省值是INSENSITIVE

无

INSENSITIVE SENSITIVE 无效组合 ---

SENSITIVE INSENSITIVE 有效组合 应用能看到自身采用 positioned 更新和删除所作的改变

SENSITIVE SENSITIVE FETCH 缺省值是SENSITIVE

应用能看到 :1. 自身采用positioned 和searched 更新和删除所作的改变2. 其他应用提交的更新和删除

DUTHow to choose the right Type of Cursor

DUT

Multiple Row Processing

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Multi-Row FETCH

What is it?

- Multi-row FETCH: A single FETCH statement can retrieve multiple rows of data from the

result table of a query as a rowset A rowset is a group of rows of data that are grouped together and

operated on as a set

Benefits

- Enhances usability and power of SQL

- Performance is improved by eliminating multiple trips between application and database engine; for distributed access, reduced network traffic

DUT

DECLARE CURSOR Example

Declare C1 as the cursor of a query to retrieve a rowset from table EMP

EXEC SQL

DECLARE C1 CURSOR

WITH ROWSET POSITONING

FOR SELECT * FROM EMP;

WITH ROWSET POSITIONING specifies whether multiple rows of data can be accessed as a rowset on a single FETCH statement.

NOTE: Do not specify the size of the rowset (FOR n ROWS) on the DECLARE CURSOR statement. That is done at FETCH time.

(FOR n ROWS clause of the FETCH statement controls how many rows are returned on each FETCH statement.)

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FETCH Examples

EXAMPLE 1:

Fetch the previous rowset and have the cursor positioned on that rowset

EXEC SQL

FETCH PRIOR ROWSET FROM C1 FOR 3 ROWS INTO……

or

EXEC SQL

FETCH ROWSET

STARTING AT RELATIVE -3 FROM C1 FOR 3 ROWS INTO……

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FETCH Examples

EXAMPLE 2:

Fetch 3 rows starting with row 20 regardless of the current position of the cursor

EXEC SQL

FETCH ROWSET STARTING AT ABSOLUTE 20

FROM C1 FOR 3 ROWS INTO……

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Host Variable Arrays

● A host variable array is an array in which each element of the array contains a value for the same column

● Can only be referenced in multi-row FETCH and INSERT

● Host variable arrays are supported in:

- COBOL

- PL/I

- C and C++

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COBOL Example

Declare cursor C1 and fetch 10 rows using a multi-row FETCH statement01 OUTPUT-VARS.

05 NAME OCCURS 10 TIMES.49 NAME-LEN PIC S9(4) USAGE COMP.49 NAME-TEXT PIC X(40).

05 SERIAL-NUMBER PIC S9(9) USAGE COMP OCCURS 10 TIMES.01 IND-VARS.

10 INDSTRUC1 PIC S9(4) USAGE COMP OCCURS 10 TIMES.10 INDSTRUC2 PIC S9(4) USAGE COMP OCCURS 10 TIMES.

PROCEDURE DIVISION.EXEC SQL

DECLARE C1 SCROLL CURSOR WITH ROWSET POSITIONING FORSELECT NAME, SERIAL FROM EMPLOYEE

END-EXEC.EXEC SQL OPEN C1 END-EXEC.EXEC SQL

FETCH FIRST ROWSET FROM C1 FOR 10 ROWSINTO :NAME:INDSTRUC1, :SERIAL-NUMBER:INDSTRUC2

END-EXEC.

DUTUsing Multi-Row FETCH with Scrollable Cursors

● As holes may occur, ensure at least one indicator variable array is defined for a column

- Even if no nullable columns exist add an indicator variable array for at least one column

- If nullable columns exist all indicator variable arrays provided are updated if a hole is found

● Value of -3 indicates hole

● SQLCODE +222 is also returned

DUTCursor Positioning: Rowset Positioned Fetches

DUT

Mixing Row and Rowset Positioning

DUT

Partial Rowsets (Result Sets)

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第五节 动态 SQL 基础 Difference between static and dynamic SQL;Difference between static and dynamic SQL;

List the type of dynamic statementsList the type of dynamic statements

Code dynamic SQL in programCode dynamic SQL in program

DUT

Static and Dynamic

仅返回一行的 SELECT 语句的结果的处理？ 通过 INTO 将结果放到宿主变量

多行呢？ 第一行放置在 INTO 字句定义地宿主变量中，同时 SQLCODE 被

置为－ 811

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Static and Dynamic

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Static Versus Dynamic

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Type of Dynamic SQL statements

DUTComplete Non-SELECT Statement

DUTComplete Non-SELECT Statement

最简单的 一旦获取语句，则 PREPARE,EXECUTE. PREPARE:即创建 ACCESS PATH. EXECUTE IMMEDIATE 会立即执行这两个功能。

DUTComplete Non-SELECT Statement

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Parameterized Non-SELECT statement

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Parameterized Non-SELECT statement

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PREPARE 语句使得 STMT 的内容，被动态 BIND. 成功，则结果可以被后面以 PRST 为名来引用之

每个 PREPARED 语句，都有一个唯一的名字，且被CACHE, 一直到这个应用中有同名语句的 PREPARE

位置参数值在 EXECUTE 的时候提供。

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SELECT statement with Fixed List

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SELECT statement with Varying List

DUT动态 SQL 语句概念

　 嵌入式动态 SQL 将获取数据的命令 ( 不是数据本身，这一点与静态SQL 不同 ) 存入宿主变量中，这些语句将由 PREPARE 语句在运行时进行预编译。

动态 SQL 需要增加 PREPARE 和 EXECUTE 语句，以便在程序运行期间创建存取路径和执行 SQL 语句。

使用动态 SQL 的样例如下： EXEC SQL DECLARE C1 CURSOR FOR S1 END-EXEC. EXEC SQL PREPARE S1 FROM :var0 END-EXEC. EXEC SQL EXECUTE S1 USING :var1,:var2 END-EXEC. EXEC SQL OPEN C1 END-EXEC. PERFORM ... UNTIL SQLCODE = +100 OR SQLCODE < 0. EXEC SQL FETCH C1 INTO ... END-EXEC. DISPLAY ... EXEC SQL CLOSE C1 END-EXEC.　其中 C1 是 CURSOR 的名字， var0 中存放动态 SQL 语句的主干部分， var1 和 var2 中存放 SQL 语句需要的参数，可选。

DUT

静态 SQL 语句与动态 SQL 语句的区别 在实际情况中，绑定包，计划和执行计划可能不是同一用

户。 1. 对于静态 SQL 语句来说，绑定包和计划的用户既需要对

应的 BIND 权限，又需要具体 SQL 语句的权限，而执行计划的用户只需要 EXECUTE 权限；

对于动态 SQL 语句来说，绑定包和计划的用户只需要对应的 BIND 权限，而执行计划的用户既需要 EXECUTE权限，又需要具体 SQL 语句的权限。

2. 静态 SQL适用于在绑定包和计划与执行计划时间间隔内表数据不频繁更新 ( 包括插入，更新和删除 ) 的情况，而动态 SQL适用于该时间间隔内表数据更新频繁的情况。

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