Structured Query Language
Structured Query Language (SQL) is a standardized language for defining and manipulating data in a relational database. In accordance with the relational model of data, the database is perceived as a set of tables, relationships are represented by values in tables, and data is retrieved by specifying a result table that can be derived from one or more base tables.
SQL statements are executed by a database manager. One of the functions of the database manager is to transform the specification of a result table into a sequence of internal operations that optimize data retrieval. This transformation occurs when the SQL statement is prepared. This transformation is also known as binding.
All executable SQL statements must be prepared before they can be executed. The result of preparation is the executable or operational form of the statement. The method of preparing an SQL statement and the persistence of its operational form distinguish static SQL from dynamic SQL.
The source form of a static SQL statement is embedded within an application program written in a host language such as COBOL, C, or Java™. The statement is prepared before the program is executed and the operational form of the statement persists beyond the execution of the program.
A source program containing static SQL statements must be processed by an SQL precompiler before it is compiled. The precompiler checks the syntax of the SQL statements, turns them into host language comments, and generates host language statements to call the database manager.
The preparation of an SQL application program includes precompilation, the preparation of its static SQL statements, and compilation of the modified source program.
Programs containing embedded dynamic SQL statements must be precompiled like those containing static SQL, but unlike static SQL, the dynamic SQL statements are constructed and prepared at run time. The source form of the statement is a character or graphic string that is passed to the database manager by the program using the static SQL PREPARE or EXECUTE IMMEDIATE statement. A statement prepared using the PREPARE statement can be referenced in a DECLARE CURSOR, DESCRIBE, or EXECUTE statement. The operational form of the statement persists for the duration of the connection or until the last SQL program leaves the call stack.
SQL statements embedded in a REXX application are dynamic SQL statements. SQL statements submitted to the interactive SQL facility and to the Call Level Interface (CLI) are also dynamic SQL statements.
Extended Dynamic SQL
An extended dynamic SQL statement is neither fully static nor fully dynamic. The QSQPRCED API provides users with extended dynamic SQL capability. Like dynamic SQL, statements can be prepared, described, and executed using this API. Unlike dynamic SQL, SQL statements prepared into a package by this API persist until the package or statement is explicitly dropped. For more information, see the Database and File APIs information in the Programming category of the IBM® i Information Center.
An interactive SQL facility is associated with every database manager. Essentially, every interactive SQL facility is an SQL application program that reads statements from a workstation, prepares and executes them dynamically, and displays the results to the user. Such SQL statements are said to be issued interactively.
The interactive facilities for Db2® for i are invoked by the STRSQL command, the STRQM command, or the Run SQL Script support of System i® Navigator. For more information about the interactive facilities for SQL, see the SQL Programming and Query Manager Use books.
SQL Call Level Interface and Open Database Connectivity
The DB2® Call Level Interface (CLI) is an application programming interface in which functions are provided to application programs to process dynamic SQL statements. DB2 CLI allows users of any of the ILE languages to access SQL functions directly through procedure calls to a service program provided by Db2 for i. CLI programs can also be compiled using an Open Database Connectivity (ODBC) Software Developer's Kit, available from Microsoft or other vendors, enabling access to ODBC data sources. Unlike using embedded SQL, no precompilation is required. Applications developed using this interface may be executed on a variety of databases without being compiled against each of the databases. Through the interface, applications use procedure calls at execution time to connect to databases, to issue SQL statements, and to get returned data and status information.
The DB2 CLI interface provides many features not available in embedded SQL. For example:
- CLI provides function calls which support a consistent way to query and retrieve database system catalog information across the DB2 family of database management systems. This reduces the need to write application server specific catalog queries.
- Stored procedures called from application programs written using CLI can return result sets to those programs.
For a complete description of all the available functions, and their syntax, see SQL Call Level Interfaces (ODBC) book.
Java DataBase Connectivity (JDBC) and embedded SQL for Java (SQLJ) programs
Db2 for i implements two standards-based Java programming APIs: Java Database Connectivity (JDBC) and embedded SQL for Java (SQLJ). Both can be used to create Java applications and applets that access DB2.
JDBC calls are translated to calls to DB2 CLI through Java native methods. You can access Db2 for i databases through two JDBC drivers: IBM Developer Kit for Java driver or IBM Toolbox for Java JDBC driver. For specific information about the IBM Toolbox for Java JDBC driver, see IBM Toolbox for Java.
Static SQL cannot be used by JDBC. SQLJ applications use JDBC as a foundation for such tasks as connecting to databases and handling SQL errors, but can also contain embedded static SQL statements in the SQLJ source files. An SQLJ source file has to be translated with the SQLJ translator before the resulting Java source code can be compiled.
For more information about JDBC and SQLJ applications, refer to the Developer Kit for Java book.
OLE DB and ADO (ActiveX Data Object)
IBM i Access for Windows includes OLE DB Providers, along with the Programmer's Toolkit to allow DB2 client/server application development quick and easy from the Windows client PC. For more information, refer to the IBM i Access for Windows OLE DB provider in the IBM i Information Center.
IBM i Access for Windows include a .NET Provider to allow DB2 client/server application development quick and easy from the Windows client PC. For more information, refer to the IBM i Access for Windows .NET provider in the IBM i Information Center.