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SQL programmingYou can use the HCL OneDB™ implementation of the SQL language to develop applications for HCL OneDB™ database servers.
Guide to SQL: SyntaxThe HCL OneDB™ Guide to SQL: Syntax describes the syntax of the statements, data types, expressions, operators, and built-in functions of the HCL OneDB™ dialect of the SQL language.
SQL statementsThis chapter describes the syntax and semantics of SQL statements that are recognized by HCL OneDB™.
SET TRANSACTION statementUse the SET TRANSACTION statement to define the isolation level and to specify whether the access mode of a transaction is read-only or read-write.
Default Isolation Levels

Default Isolation Levels

The default isolation level is established when you create the database.


HCL OneDB™ Name	ANSI Name	When This Is the Default Level of Isolation
Dirty Read	Read Uncommitted	Database without transaction logging
Committed Read	Read Committed	Databases with logging that are not ANSI- compliant
Repeatable Read	Serializable	ANSI-compliant databases

For HCL OneDB databases that are not ANSI-compliant, unless you explicitly set the USELASTCOMMITTED configuration parameter, the LAST COMMITTED feature is not in effect for the default isolation levels. The SET ENVIRONMENT statement or the SET ISOLATION statement can override this default and enable LAST COMMITTED for the current session.

The default isolation level remains in effect until you issue a SET TRANSACTION statement within a transaction. After a COMMIT WORK statement completes the transaction or a ROLLBACK WORK statement cancels the entire transaction, the isolation level is reset to the default.

When you use High Availability Data Replication, the database server effectively uses Dirty Read isolation on the HDR Secondary Server, regardless of the specified SET ISOLATION or SET TRANSACTION isolation level, unless the UPDATABLE_SECONDARY configuration parameter is enabled. For more information about this topic, see Isolation Levels for Secondary Data Replication Servers.