Q. What will the EXPLAIN do?
A EXPLAIN obtains information (which indexes are used, whether sorting is necessary, which level of locking is applied) about how SQL statements in the DBRM will be executed, inserting this information into "X".PLAN_TABLE where "X" is the authorization ID of owner of the plan.
Q. What is a foreign key?
A A foreign key is a column (or combination of columns) in a table whose values are required to match those of the primary key in some other table.
Q. What will the FREE command do to a plan?
A It will drop (delete) that existing plan.
Q. What will the GRANT option do?
A It will grant privileges to a list of one or more users. If the GRANT option is used in conjunction with the "PUBLIC" option, then all users are granted privileges. Also, you can grant privileges by objects and types.
Q. What does the term "grant privileges" mean?
A Grant privileges means giving access/authority to DB2 users.
Q. What is a host variable?
A This is a data item that is used in an SQL statement to receive a value or to supply a value. It must be preceded by a colon (:) to tell DB2 that the variable is not a column name.
Q. What is an image copy?
A It is an exact reproduction of all or part of a tablespace. DB2 provides utility programs to make full-image copies (to copy the entire tablespace) or incremental image copies to copy only those pages that have been modified since the last image copy.
Q. What is meant by an index?
A An index is a set of row identifiers (RIDS) or pointers that are logically ordered by the values of a column that has been specified as being an index. Indexes provide faster access to data and can enforce uniqueness on the row in a table.
Q. What is an index key?
A It is a column or set of columns in a table used to determine the order of index entries.
Q. What is meant by an index scan?
A. When an entire index (or a portion thereof) is scanned to locate rows, we call this an index scan. This type of access can be used, for example, to select rows of a table in some order and avoid sort for a query.
Q. What is meant by indicator variable?
A An indicator variable is an integer variable used to show whether its associated host variable has been assigned a null value.
Q. What is a join?
A A join is a relational operation that allows retrieval of data from two or more tables based on matching column values.
Q. What is meant by locking?
A Locking is a process that is used to ensure integrity of data. It also prevents concurrent users from accessing inconsistent data. The data (row) is locked until a commit is executed to release the updated data.
Q. What is a “nonleaf” page?
A This is a page that contains keys and page numbers of other pages in the index. Nonleaf pages never point to actual data.
Q. What is meant by null?
A This is a special value that indicates the absence of data in a column. This value is indicated by a negative value, usually -1.
Q. What is an object?
A An object is anything that is managed by DB2 (that is, databases, tablespaces, tables, views, indexes, or synonyms), but not the data itself.
Q. What will the DB2 optimizer do?
A The optimizer is a DB2 component that processes SQL statements and selects the access paths.
Q. What is a page?
A This is the unit of storage within a tablespace or indexspace that is accessed by DB2.
Q. What is a pagespace?
A Pagespace refers either to an unpartitioned table to an index space, or to a single partition of a partitioned table of index space.
Q. What is a predicate?
A A predicate is an element of a search condition that expresses or implies a comparison operation.
Q. Describe a primary key?
A A primary key is a key that is unique, nonnull and is part of the definition of a table. A table must have a primary key to be defined as parent.
Q. What is a recovery log?
A A recovery log is a collection of records that describes sequence of events that occur in DB2. The information is needed for recovery in the event of a failure during execution.
Q. What is a Resource Control Table (RCT)? Describe its characteristics?
A The RCT is a table that is defined to a DB2/CICS region. It contains control characteristics which are assembled via the DSNCRCT macros. The RCT matches the CICS transaction ID to its associated DB2 authorization ID and plan ID (CICS attachment facility).
Q. Where are plans stored?
A Each plan is defined uniquely in the SYSIBM.SYSPLAN table to correspond to the transactions that are to execute that plan.
Q. Describe referential integrity?
A Referential integrity refers to a feature in DB2 that is used to ensure consistency of data in the database.
Q. What is meant by a repeatable read?
A When an application program executes with repeatable read protection, rows referenced by the program cannot be changed by other programs until the program reaches a commit point.
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