Explanation:It will create a unique index. For a unique index, one ROWID exists for each data value but in a non-unique index the ROWID is included in the key of sorter order. Composite Indexes When an index is
SQL UNIQUE Constraint on CREATE TABLE The following SQL creates aUNIQUEconstraint on the "ID" column when the "Persons" table is created: SQL Server / Oracle / MS Access: CREATETABLEPersons ( ID intNOTNULLUNIQUE, LastName varchar(255)NOTNULL, ...
Explanation: Here, each customer and their email have a unique ID. 4. FOREIGN KEY Constraint in SQL A foreign key constraint in SQL is used to create a relationship between two tables. It works by referring to the primary key of another table. The primary key uniquely identifies each reco...
The Join Operation - an explanation of how to use indexes to perform a fast table join Clustering Data - the difference between selecting a single column and all columns Sorting and Grouping - even order by and group by can use indexes Partial Results - explains how to benefit from a "pipe...
Oracle Database SQL Language Referencefor an explanation of the differences between Oracle SQL and standard SQL SQL*Plus User's Guide and Referencefor SQL*Plus commands, including their distinction from SQL statements Parent topic:Introduction to SQL ...
Structure of the tables referenced in the SQL statement (usually by describing the table in SQL*Plus) Definitions of any indexes (columns, column orderings), and whether the indexes are unique or nonunique CBO statistics for the segments (including the number of rows each table, selectivity of...
Explanation No RESTART or TERMINATE is necessary. The RESTART and TERMINATE modes of the LOAD utility should be used to resume or cancel a previously failed/interrupted LOAD operation. They are only supported on tables where a previous load operation failed and the table is in LOAD PENDING state...
Explanation The partitioned table was defined with NO CYCLE and there are not enough table spaces defined for the number of specified table partitions. The statement cannot be processed. User response In the CREATE TABLE statement, either specify additional table spaces for the table or remove the...
The benefits of unique indexes include the following: Data integrity of the defined columns is ensured. Additional information helpful to the query optimizer is provided. Creating a PRIMARY KEY or UNIQUE constraint automatically creates a unique index on the specified columns. There are no signific...
The benefits of unique indexes include the following: Data integrity of the defined columns is ensured. Additional information helpful to the query optimizer is provided. Creating a PRIMARY KEY or UNIQUE constraint automatically creates a unique index on the specified columns. There are no significant...