Query optimization is a function of many relational database management systems. The query optimizer attempts to determine the most efficient way to execute a given. Spring MVC Form Binding. Before you start the tutorial, you need to understand how the Spring MVC form binding works. 1.1 In controller, you add an object into a. Concepts, examples, and common problems. Understanding DB2 system and user application packages. John Chun and Paolo Cirone. Published on June 0. What are. packages? This controller lets you send an FTP "retrieve file" or "upload file" request to an FTP server. If you are going to send multiple requests to the same FTP server.Packages in DB2 are control- structure database objects that contain. SQL statements or placement holders for executable. In DB2 for Linux®, UNIX®, and Windows®, packages. Packages are stored in the. If an application intends to access a database using static SQL, the. SQL statements in the. When the program source code is converted to an. SQL) or executed (dynamic SQL), the strategy for. SQL statement is stored in a package as a single. Each section is a bound form of the embedded SQL statement, and. DB2 packages are used to execute SQL statements on the database server. They play a crucial role in how a DB2 client application interacts with. DB2 server. Common use of. DB2 Runtime Client. The DB2. Runtime Client does not include any DB2 bind files. The task of binding is. Providing bind files to all general users who have access to the Runtime. Client environment would go against the general rule of leaving bind tasks. The general use of packages in DB2 can be categorized into two areas: DB2 system packages: This set of packages is. DB2 products (with the exception of the run time. It consists of utilities and drivers that are required by DB2. Embedded SQL packages: The second set includes. The following sections discuss the use of both kinds of packages in. DB2 system. packages. The following are list files (*. DB2 product. Binding must be done once per db. DB2 server the. given installed code connects to. Here are the typical commands used to bind system packages from the command. DB2 Linux, UNIX, and Windows databases: Listing 1. Commands to bind system packagesbind BNDPATH/@db. BNDPATH/@db. 2cli. All host database systems have their own *. DB2 for z/OS® and OS/3. DB2 for VM®ddcsvse. DB2 for VSE®ddcs. DB2 for AS/4. 00® and i. Series™The *. lst files are simple text files that contain a list of bind (*. When binding the list file, you must specify the '@' character (at. Among the various system packages, this article concentrates on the CLI. Packages for each db. They are specific to each DB2 fix. DB2 in your environment (at least once at install time). Every new DB2 fix pack may have changes built into system packages. These. changes result from APARs (defects) or feature additions. Changes to. system packages will result in a change to the package names. This change. to package naming is done to ensure that the new package does not. The existing client would require previously bound. If the names were not changed as required, there would be no way to easily. Historically, DB2 would always have a unique package name depending on the. This design resulted in many unnecessary packages on the server over time. In DB2 UDB Version 7. DB2 packages. With the installation of any new fix pack, a user with BINDADD authority on. DB2 Call Level. Interface (CLI) packages. The DB2 Call Level Interface (DB2 CLI) is a callable SQL interface to the. DB2 family of database servers. A callable SQL interface is an application. API) for database access, which uses function calls to. SQL statements. It is an alternative to embedded dynamic. SQL, but unlike embedded SQL, it does not require precompiling or binding. DB2 CLI is based on the Microsoft® Open Database Connectivity (ODBC). X/Open specification. Autobind. Autobind has a. These. disadvantages include performance issues (extra network traffic) and. You should always perform system. The DB2 CLI driver automatically creates DB2 packages required at. This is known as. If a package already exists, the driver uses the existing. These packages are also required to be bound when fix packs are upgraded. By default, DB2 packages created by. DB2 driver are created in the NULLID collection (or library). A dynamic section is the actual executable object that contains the logic. SQL request. Each statement handle allocated. CLI application will occupy one section within a CLI package. In some cases, you may need to create additional DB2 CLI packages that in. Should. your application require more than the default number of sections (if you. The CLIPKG option discussed below demonstrates how to create. CLI packages. CLI package naming convention. For each CLI bind file, generate multiple packages with different package. The number of packages generated is equal to the number of. TIMES the value of the CLIPKG bind option. The default is. three for the CLIPKG option. Theoretically, CLIPKG can be a maximum of 2. That is the limit due to our naming convention. Figure 1. Naming. CLI packages. View image at full size. The cursors in the packages follow the naming convention in. Listing 2: Listing 2. Naming convention for cursors. Example: SQL_CURLH1. C3. 84. SQL : constant for all cursors. L or S: package size. H or N: hold or nohold. Cursor : constant for all cursors. Table 1. DB2 CLI bind files and package. Bind file name. Package name. Needed by DB2 Universal Database. Needed by host servers. Descriptiondb. 2clipk. SYSSHxyy. Yes. Yes. Dynamic placeholders - small package WITH HOLDdb. SYSSNxyy. Yes. Yes. Dynamic placeholders - small package NOT WITH HOLDdb. SYSLHxyy. Yes. Yes. Dynamic placeholders - large package WITH HOLDdb. SYSLNxyy. Yes. Yes. Dynamic placeholders - large package NOT WITH HOLDdb. SYSSTATYes. Yes. Common static CLI functionsdb. SQLL9. Eyy. Yes. No. Catalog function supportdb. SQLL6. 5zz. Server Version 2 to 7. No. DB2 for Intel/UNIX catalog function supportdb. SQLL9. 5zz. Server Version 2 to 7. No. Common static CLI functions. Notes for Table 1: 'S' represents a small package, and 'L' represents a large. H' represents WITH HOLD, and 'N' represents NOT WITH HOLD'x' is the isolation level: 0=NC, 1=UR, 2=CS, 3=RS, 4=RR'yy' is the package iteration 0. FF'zz' is unique for each platform. For example, for the dynamic packages: SYSSN1. A small package (6. Bound with isolation level UR. This is the first iteration of that package. SYSLH4. 01 - A large package (3. Bound with isolation level RS. This. is the second iteration of that package. Bind options used for CLI Packages. CLI packages are automatically bound with ACTION ADD. Therefore, once the. SQLCODE of - 7. 19 or - 7. The. binder turns off this - 7. However, if a DB2 trace is taken, the - 7. The ACTION. ADD speeds up the binding process by only creating the package if it does. NOT exist. Should the package already exist, under the covers, you would. SQLCODEs denoted above and binding would stop. ACTION ADD. eliminates lock contention for replacing already existing packages. ACTION ADD is only sent to Linux, UNIX, and Windows and z/OS. Do not send. it to other servers (for example, VSE, VM, OS4. When binding CLI, ignore all user- specified options, except ACTION. REPLVER, COLLECTION, and CLIPKG (other than options specified in the bind. However, if COLLECTION has been specified, then all options are. Package sections and their impact on CLIThe use of packages poses a theoretical limit on the number of handles any. CLI) can allocate. Version 7 had a maximum. Version 8 has a maximum limit of. It is possible to allocate up to 1. Note that in addition to a theoretical limit, physical resource. The maximum theoretical number of sections that may be used at one time. CLI application is 1. By default, three sections from each. This is done since an UPDATE/DELETE WHERE CURRENT OF. UPDATE/DELETE originated. Since there are a maximum of 3. X3) sections in total. That means real available sections or. So an application working with only CS isolation and HOLD cursors would. If, however, the application used a. WITHOUT HOLD cursors as well as CS and HOLD. CURSORs, it is possible to hit the maximum statement limit of 1. Package associated CLI keywords. CLI keywords are set in the db. An application will load and. You. will find a copy of the db. DB2. So ensure that any application- driven changes to the db. Keywords are only read from the db. You can find a list of CLI keywords in. Table 2. JDBC. packages. Both the Legacy CLI- based JDBC and the Universal JDBC T2/T4 drivers use the. CLI driver discussed above. This piece of information. CLI packages. bound to it for the level of code your JDBC driver is based on, you do not. You are free to use them. The reverse is. also true - - should you have the need to perform a bind against a newly. JDBC driver, once the packages are created, all. JDBC and CLI applications are free to use. Any CLI application does not. Note: Again, remember packages may be different for every fix pack. Comparison of different SQL implementations. The goal of this page — which is a work in progress — is to gather information relevant for people who are porting SQL from. SQL. The following tables compare how different. DBMS products handle various SQL (and related) features. If possible, the tables also. SQL. standard. I will only write about subjects that I've worked with personally, or. I anticipate to find use for in the near future. Subjects on which there are no significant implementation variances are not. Beta- versions of software are not examined. I'm sorry about the colors. They are a result of wanting to mark each DBMS. If you have corrections or suggestions, please. The following SQL standard and implementations have been. This is important for My. SQL and MSSQL: Their interpretation of SQL. My. SQL, there is a dedicated documentation page about this). However, such. non- default configuration options are not of great value for people. SQL applications because the developer often cannot rely on non- default. Views are part of the standard, and they may be updated, as long as it 'makes sense'. SQL: 2. 00. 8 has a rather complicated set of rules governing when a view is updatable, basically saying that a view is updatable, as long as the update- operation translates into an unambiguous change. SQL- 9. 2 was more restrictive, specifying that updatable views cannot be derived from more than one base table. Has views. Breaks that standard by not allowing updates to views; offers the non- standard 'rules'- system as a work- around. Conforms to at least SQL- 9. Conforms to at least SQL- 9. Conforms to at least SQL- 9. Conforms to at least SQL- 9. Conforms to at least SQL- 9. All the DBMSes support basic INNER JOINs, but vary in their support for other join types. In the following feature chart, a. Remarks: Note that FULL joins may be emulated with a union of a left and a right join. Objective: An existing table, t. I. e., only the structure/definition of the table is copied. Optional feature T1. LIKE clause in table definition. CREATE TABLE t. 2 ( LIKE t. The DBMS may support an extension of this (feature T1. CREATE TABLE t. 2 ( LIKE t. INCLUDING IDENTITY INCLUDING DEFAULTS INCLUDING GENERATED )If INCLUDING DEFAULTS is not specified, column defaults will not be part of t. IDENTITY and GENERATED properties. Triggers, CHECK constraints, and other 'non- trivial' table features are not copied to the new table. Complies with the core of the feature (T1. The extended T1. 73 feature is only partially supported, and extended with a few non- standard options. The INCLUDING IDENTITY and INCLUDING GENERATED options are not supported. INCLUDING CONSTRAINTS and INCLUDING INDEXES options are added. Postgre. SQL does not allow you to copy the structure of a view, using CREATE TABLE .. LIKE ..). For that, you may use another construct: CREATE TABLE copytable AS SELECT * FROM viewname WHERE false. Documentation. Behaves as if inspired by the standard. I. e., DB2 conforms to the standard, except. LIKE .. clause is stated outside any parenthesisthe extended INCLUDING GENERATED option is not supported. DB2 defaults to copy IDENTITY, DEFAULTS, and GENERATED properties, unless EXCLUDING IDENTITY and/or EXCLUDING DEFAULTS is specified. Example. CREATE TABLE t. LIKE t. 1 INCLUDING DEFAULTSDB2 allows you to copy the structure of a view into a table. Documentation. Does not support the standard. Instead, MSSQL has a special SELECT .. INTO .. FROM .. construct which can be combined with an impossible WHERE- clause to copy structure only. SELECT * INTO t. 2 FROM t. WHERE 1< > 1. The source (t. 1) may be a view, as well as a table. SELECT .. INTO copies NOT NULL column attributes, but nothing else. Documentation. Complies with the core of the feature (T1. T1. 73). My. SQL does not allow you to copy the structure of a view into a table. Documentation. Does not support the standard. Oracle lets you copy a table structure using a special CREATE TABLE .. AS construct, combined with an impossible WHERE- clause. CREATE TABLE t. 2 AS SELECT * FROM t. WHERE 1< > 1. Documentation. On my TODO. The SQL- standard states that relations are unordered, but. DECLARE cursorname CURSOR FORSELECT .. FROM .. WHERE .. ORDER BY column_name. The DBMS may additionally allow ORDER BY outside cursor definitions (optional feature IDs F8. F8. 51, F8. 52, F8. Since SQL: 2. 00. NULLs should be ordered in comparison with. NULL values, except that any two NULLs are to be considered equally ordered, and. NULLs should sort either above or below all non- NULL values. However, the DBMS may. ID T6. 11, "Elementary OLAP operations"). NULLs should sort first or last. ORDER BY .. NULLS FIRSTor. ORDER BY .. NULLS LASTAs well as in cursor definitions, it allows ORDER BY in other contexts. By default, NULLs are considered higher than any non- NULL value; however,(since version 8. NULLS FIRST or NULLS LAST to the ORDER BY expression. DOCUMENTATIONAs well as in cursor definitions, it allows ORDER BY in other contexts. NULLs are considered higher than any non- NULL value. DOCUMENTATIONAs well as in cursor definitions, it allows ORDER BY in other contexts. NULLs are considered lower than any non- NULL value. DOCUMENTATIONAs well as in cursor definitions, it allows ORDER BY in other contexts. NULLs are considered lower than any non- NULL value. ASC is changed to DESC, or DESC to ASC; this minus- before- column- name. Documentation. As well as in cursor definitions, it allows ORDER BY in other contexts. By default, NULLs are considered higher. NULL value; however, this sorting behaviour may be changed. NULLS FIRST or NULLS LAST. ORDER BY expression. Beware of Oracle's strange treatment of empty strings and NULLs as. DOCUMENTATIONAs well as in cursor definitions, it allows ORDER BY in other contexts. NULLs are considered lower than any non- NULL value. DOCUMENTATIONObjective: Want to only get n rows in the result set. Usually only makes sense in connection with an ORDER BY expression. Note: This is not the same as a top- n query — see next section. Note also: Some of the queries below may not be legal in all situations, such as in views or sub- queries. By the way, Use The Index, Luke! The SQL standard provides three ways of performing a 'simple limit'. Using FETCH FIRST: (since SQL: 2. Non- core feature IDs F8. F8. 57, F8. 58, and F8. SELECT .. FROM .. WHERE .. ORDER BY .. FETCH FIRST n ROWS ONLYYou may write ROW instead of ROWS. Using a Window function: (since SQL: 2. Non- core Feature ID T6. ROW_NUMBER() OVER. SELECT * FROM (SELECTROW_NUMBER() OVER (ORDER BY key ASC) AS rownumber,columns. FROM tablename) AS foo. WHERE rownumber < = n. Using a cursor. If your application is stateful (in contrast to web applications which. ID E1. 21) instead. This involves: DECLARE cursor- name CURSOR FOR .. OPEN cursor- name. FETCH .. CLOSE cursor- name. Supports all standards- based approaches. In old Postgre. SQL versions (versions 8. Postgre. SQL (and My. SQL) specific method was used. SELECT columns. FROM tablename. ORDER BY key ASCLIMIT n. Note that LIMITchanges the semantics of SELECT.. FOR UPDATE. Documentation: Supports all standards- based approaches. Documentation: OLAP functions. FETCH FIRST (general page about the SELECT statement; use your browser's search function to locate FETCH FIRST). Supports the ROW_NUMBER()(since MSSQL 2. FETCH FIRST. MSSQL 2. ROW_NUMBER(). Instead, a MSSQL 2. SELECT TOP ncolumns. FROM tablename. ORDER BY key ASC. The TOP construct is still available in MSSQL 2. SQL work. Documentation. Doesn't support the standard. Alternative solution. SELECT columns. FROM tablename. ORDER BY key ASCLIMIT n. Documentation. Supports ROW_NUMBER; doesn't support FETCH FIRST. As Oracle doesn't allow AS for subquery naming (and doesn't need a subquery- name at all in this case), the standard SQL code above needs to be rewritten slightly: SELECT * FROM (SELECTROW_NUMBER() OVER (ORDER BY key ASC) AS rownumber,columns. FROM tablename)WHERE rownumber < = n. Documentation. A reader of this page told me that using the Oracle- specific ROWNUM 'magic' column yields better performance than using the ROW_NUMBER function. You may want to experiment with this. Ask Tom has an article on ROWNUM. Supports neither ROW_NUMBER(), nor FETCH FIRST. Alternative solution (which is illegal in plain sub- queries). SELECT FIRST ncolumns. FROM tablename. ORDER BY key ASCDocumentation. Objective: Like the simple limit- query above, but include. Thus, the query may return more than n. Some call this a quota- query.
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