CREATE INDEX statement

Description

Creates an index on a specified table, or pair of tables.

Syntax

CREATE [ UNIQUE ] [ index-type ] INDEX index-name
... ON [ owner.]table-name
... ( column-name [, column-name ] ...)
... [ { IN | ON } dbspace-name ]
... [ NOTIFY integer ]
... [ DELIMITED BY separators-string ‘ ]
... [ LIMIT maxwordsize-integer ]

Parameters

index-type:

{ CMP | HG | HNG | LF | WD | DATE | TIME | DTTM }

Examples

Example 1

CREATE 
CMP INDEX proj_curr_cmp
ON sales_data
( projected_earnings, current_earnings )
CREATE HG INDEX item_prod_hg
ON sales_order_items
( prod_id )
CREATE LF INDEX item_prod
ON sales_order_items
( prod_id )
 NOTIFY 0
CREATE WD INDEX earnings_wd
ON earnings_report_table(varchar)
DELIMITED BY ‘ :;.’
LIMIT 25
CREATE DTTM INDEX order_dttm
ON sales_order
( order_date )

Usage

The CREATE INDEX statement creates an index on the specified column of the named table. Once an index is created, it is never referenced in a SQL statement again except to delete it using the DROP INDEX statement.

For columns in Sybase IQ tables, you can specify an index-type of HG (High_Group), HNG (High_Non_Group), LF (Low_Fast), WD (Word), DATE, TIME, or DTTM (Datetime). If you do not specify an index-type, an HG index is created by default.

To create an index on the relationship between two columns in an IQ table, you can specify an index-type of CMP (Compare). Columns must be of identical data type, precision and scale. For a CHAR, VARCHAR, BINARY or VARBINARY column, precision means that both columns have the same width.

For maximum query speed, the correct type of index for a column depends on:

The Sybase IQ System Administration Guide describes the index types in detail and tells how to determine the appropriate index types for your data.

You can specify multiple indexes on a column of an IQ table, but these must be of different index types. CREATE INDEX does not let you add a duplicate index type. Sybase IQ chooses the fastest index available for the current query or portion of the query. However, each additional index type might significantly add to the space requirements of that table.

column-name Specifies the name of the column to be indexed. A column name is an identifier preceded by an optional correlation name. (A correlation name is usually a table name. For more information on correlation names, see FROM clause.) If a column name has characters other than letters, digits, and underscore, enclose it in quotation marks (“”).

When you omit UNIQUE, you can specify only an HG index. Foreign keys require nonunique HG indexes and composite foreign keys require nonunique composite HG indexes. The multicolumn composite key for both unique and nonunique HG indexes has a maximum width of 5300 bytes. CHAR or VARCHAR data cannot be more than 255 bytes when it is part of a composite key or single-column HG, LF, HNG, DATE, TIME, or DTTM indexes.

UNIQUE UNIQUE ensures that no two rows in the table have identical values in all the columns in the index. Each index key must be unique or contain a NULL in at least one column. You can create unique HG indexes with more than one column, but you cannot create multicolumn indexes using other index types. You cannot specify UNIQUE with the CMP, HNG, WD, DATE, TIME, or DTTM index types.

Sybase IQ allows the use of NULL in data values on a user created unique multicolumn HG index, if the column definition allows for NULL values and a constraint (primary key or unique) is not being enforced. See “Multicolumn indexes” in “Notes” for more information.

Index placement An index is always placed in the same type of dbspace (IQ Store or Temporary Store) as its table. When you load the index, the data is spread across any database files of that type with room available. Although the CREATE INDEX command lets you specify the dbspace-name IQ_SYSTEM_TEMP or IQ_SYSTEM_MAIN, this option has no real effect for Sybase IQ indexes. Sybase IQ ensures that any dbspace-name you specify is appropriate for the index. If you try to specify IQ_SYSTEM_MAIN for indexes on temporary tables, or vice versa, you receive an error. Dbspace names are case sensitive for databases created with CASE RESPECT.

DELIMITED BY Specifies separators to use in parsing a column string into the words to be stored in that column’s WD index. If you omit this clause or specify the value as an empty string, Sybase IQ uses the default set of separators. The default set of separators is designed for the default collation order (ISO-BINENG). It includes all 7-bit ASCII characters that are not 7-bit ASCII alphanumeric characters, except for the hyphen and the single quotation mark. The hyphen and the single quotation mark are part of words by default. There are 64 separators in the default separator set. For example, if the column value is this string:

The cat is on the mat

and the database was created with the CASE IGNORE setting using default separators, the following words are stored in the WD index from this string:

cat is mat on the

If you specify multiple DELIMITED BY and LIMIT clauses, no error is returned, but only the last clause of each type is used.

separators-string The separators string must be a sequence of 0 or more characters in the collation order used when the database was created. Each character in the separators string is treated as a separator. If there are no characters in the separators string, the default set of separators is used. (Each separator must be a single character in the collation sequence being used.) There cannot be more than 256 characters (separators) in the separators string.

To specify tab as a delimiter, you can either type a <TAB> character within the separator string, or use the hexadecimal ASCII code of the tab character, \x09. “\t” specifies two separators, \ and the letter t. To specify newline as a delimiter, you can type a <RETURN> character or the hexadecimal ASCII code \x0a.

For example, the clause DELIMITED BY ' :;.\/t' specifies these seven separators: space : ; . \ / t

Table 6-6: Tab and newline as delimiters

For these delimiters

Use this separators string in the DELIMITED BY clause

tab

' ' (type <TAB>)or

'\x09'

newline

' ' (type <RETURN>) or '\x0a'

LIMIT Can be used for the creation of the WD index only. Specifies the maximum word length that is permitted in the WD index. Longer words found during parsing causes an error. The default is 255 bytes. The minimum permitted value is 1 and the maximum permitted value is 255. If the maximum word length specified in the CREATE INDEX statement or determined by default exceeds the column width, the used maximum word length is silently reduced to the column width. Using a lower maximum permitted word length allows insertions, deletions, and updates to use less space and time. The empty word (two adjacent separators) is silently ignored. After a WD index is created, any insertions into its column are parsed using the separators and maximum word size determined at create time. These separators and maximum word size cannot be changed after the index is created.

NOTIFY Gives notification messages after n records are successfully added for the index. The messages are sent to the standard output device. A message contains information about memory usage, database space, and how many buffers are in use. The default is 100,000 records. To turn off NOTIFY, set it to 0.


Notes

WARNING!  Using the CREATE INDEX command on a local temporary table containing uncommitted data fails and generates the following error message: “Local temporary table, <tablename>, must be committed in order to create an index.” Commit the data in the local temporary table before creating an index.


Side effects

Automatic commit.

Standards

Adaptive Server Enterprise indexes can be either clustered or nonclustered. A clustered index almost always retrieves data faster than a nonclustered index. Only one clustered index is permitted per table.

Sybase IQ does not support clustered indexes. The CLUSTERED and NONCLUSTERED keywords are allowed by SQL Anywhere, but are ignored by Sybase IQ. If no index-type is specified, Sybase IQ creates an HG index on the specified column(s).

Sybase IQ does not permit the DESC keyword.

Sybase IQ also allows, by ignoring, the following keywords:

Index names must be unique on a given table for both Sybase IQ and Adaptive Server Enterprise.

Permissions

Must be the owner of the table or have DBA authority.

See also

CREATE JOIN INDEX statement

DROP statement

INDEX_PREFERENCE option

Chapter 6, “Using Sybase IQ Indexes,” in the Sybase IQ System Administration Guide.