CREATE INDEX¶
Function¶
CREATE INDEX creates an index in a specified table.
Indexes are primarily used to enhance database performance (though inappropriate use can result in slower database performance). You are advised to create indexes on:
Columns that are often queried
Join conditions. For a query on joined columns, you are advised to create a composite index on the columns, for example, select * from t1 join t2 on t1.a=t2.a and t1.b=t2.b. You can create a composite index on the a and b columns of table t1.
Columns having filter criteria (especially scope criteria) of a where clause
Columns that appear after order by, group by, and distinct.
Create a B-tree index for point queries.
The partitioned table does not support concurrent index creation, partial index creation, and NULL FIRST.
Precautions¶
Indexes consume storage and computing resources. Creating too many indexes has negative impact on database performance (especially the performance of data import. Therefore, you are advised to import the data before creating indexes). Create indexes only when they are necessary.
All functions and operators used in an index definition must be immutable, that is, their results must depend only on their parameters and never on any outside influence (such as the contents of another table or the current time). This restriction ensures that the behavior of the index is well-defined. When using a user-defined function on an index or in a WHERE statement, mark it as an immutable function.
A unique index created on a partitioned table must include a partition column and all the partition keys.
GaussDB(DWS) can only create local indexes on partitioned tables.
Column-store tables and HDFS tables support B-tree indexes. If the B-tree indexes are used, you cannot create expression and partial indexes.
Column-store tables support creating unique indexes using B-tree indexes.
Column-store and HDFS tables support psort indexes. If the psort indexes are used, you cannot create expression, partial, and unique indexes.
Column-store tables support GIN indexes, rather than partial indexes and unique indexes. If GIN indexes are used, you can create expression indexes. However, an expression in this situation cannot contain empty splitters, empty columns, or multiple columns.
A primary key or unique index cannot be created for a round-robin table.
Performing CREATE INDEX or REINDEX operations on a table triggers index rebuilding. During this process, data is dumped to a new data file, and once rebuilding is complete, the original file is deleted. For large tables, index rebuilding can consume a significant amount of disk space. Exercise caution when disk space is insufficient to prevent the cluster from becoming read-only.
Syntax¶
Create an index on a table.
CREATE [ UNIQUE ] INDEX [ [ schema_name. ] index_name ] ON table_name [ USING method ] ({ { column_name | ( expression ) } [ COLLATE collation ] [ opclass ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] }[, ...] ) [ NULLS [ NOT ] DISTINCT | NULLS IGNORE ] [ COMMENT 'text' ] [ WITH ( {storage_parameter = value} [, ... ] ) ] [ WHERE predicate ];
Create an index for a partitioned table.
CREATE [ UNIQUE ] INDEX [ [ schema_name. ] index_name ] ON table_name [ USING method ] ( {{ column_name | ( expression ) } [ COLLATE collation ] [ opclass ] [ ASC | DESC ] [ NULLS LAST ] }[, ...] ) [ NULLS [ NOT ] DISTINCT | NULLS IGNORE ] [ COMMENT 'text' ] LOCAL [ ( { PARTITION index_partition_name } [, ...] ) ] [ WITH ( { storage_parameter = value } [, ...] ) ] ;
Parameters¶
UNIQUE
Causes the system to check for duplicate values in the table when the index is created (if data exists) and each time data is added. Attempts to insert or update data which would result in duplicate entries will generate an error.
Currently, only B-tree indexes of row-store tables and column-store tables support unique indexes.
schema_name
Name of the schema where the index to be created is located. The specified schema name must be the same as the schema of the table.
index_name
Specifies the name of the index to be created. The schema of the index is the same as that of the table.
Value range: a string. It must comply with the naming convention.
table_name
Specifies the name of the table to be indexed (optionally schema-qualified).
Value range: an existing table name
USING method
Specifies the name of the index method to be used.
Valid value:
btree: The B-tree index uses a structure that is similar to the B+ tree structure to store data key values, facilitating index search. btree supports comparison queries with ranges specified.
gin: GIN indexes are reverse indexes and can process values that contain multiple keys (for example, arrays).
gist: GiST indexes are suitable for the set data type and multidimensional data types, such as geometric and geographic data types.
Psort: psort index. It is used to perform partial sort on column-store tables.
Row-based tables support the following index types: btree (default), gin, and gist. Column-based tables support the following index types: Psort (default), btree, and gin.
column_name
Specifies the name of a column of the table.
Multiple columns can be specified if the index method supports multi-column indexes. A maximum of 32 columns can be specified.
expression
Specifies an expression based on one or more columns of the table. The expression usually must be written with surrounding parentheses, as shown in the syntax. However, the parentheses can be omitted if the expression has the form of a function call.
Expression can be used to obtain fast access to data based on some transformation of the basic data. For example, an index computed on upper(col) would allow the clause WHERE upper(col) = 'JIM' to use an index.
If an expression contains IS NULL, the index for this expression is invalid. In this case, you are advised to create a partial index.
COLLATE collation
Assigns a collation to the column (which must be of a collatable data type). If no collation is specified, the default collation is used.
opclass
Specifies the name of an operator class. Specifies an operator class for each column of an index. The operator class identifies the operators to be used by the index for that column. For example, a B-tree index on the type int4 would use the int4_ops class; this operator class includes comparison functions for values of type int4. In practice, the default operator class for the column's data type is sufficient. The operator class applies to data with multiple sorts. For example, we might want to sort a complex-number data type either by absolute value or by real part. We could do this by defining two operator classes for the data type and then selecting the proper class when making an index.
ASC
Indicates ascending sort order (default). This option is supported only by row storage.
DESC
Indicates descending sort order. This option is supported only by row storage.
NULLS FIRST
Specifies that nulls sort before not-null values. This is the default when DESC is specified.
NULLS LAST
Specifies that nulls sort after not-null values. This is the default when DESC is not specified.
NULLS [ NOT ] DISTINCT | NULLS IGNORE
Specifies how NULL values of index columns in a Unique index are processed.
Default value: This parameter is left empty by default. NULL values can be inserted repeatedly.
When the inserted data is compared with the original data in the table, the NULL value can be processed in any of the following ways:
NULLS DISTINCT: NULL values are unequal and can be inserted repeatedly.
NULLS NOT DISTINCT: NULL values are equal. If all index columns are NULL, NULL values cannot be inserted repeatedly. If some index columns are NULL, data can be inserted only when non-null values are different.
NULLS IGNORE: NULL values are skipped during the equivalent comparison. If all index columns are NULL, NULL values can be inserted repeatedly. If some index columns are NULL, data can be inserted only when non-null values are different.
The following table lists the behaviors of the three processing modes.
Table 1 Processing of NULL values in index columns in unique indexes¶ Constraint
All Index Columns Are NULL
Some Index Columns Are NULL.
NULLS DISTINCT
Can be inserted repeatedly.
Can be inserted repeatedly.
NULLS NOT DISTINCT
Cannot be inserted repeatedly.
Cannot be inserted if the non-null values are equal. Can be inserted if the non-null values are not equal.
NULLS IGNORE
Can be inserted repeatedly.
Cannot be inserted if the non-null values are equal. Can be inserted if the non-null values are not equal.
COMMENT 'text'
Specifies the comment of an index.
WITH ( {storage_parameter = value} [, ... ] )
Specifies the name of an index-method-specific storage parameter.
Valid value:
Only the GIN index supports the FASTUPDATE and GIN_PENDING_LIST_LIMIT parameters. The indexes other than GIN and psort support the FILLFACTOR parameter. All indexes support the INVISIBLE parameter.
FILLFACTOR
The fillfactor for an index is a percentage between 10 and 100.
Value range: 10-100
FASTUPDATE
Specifies whether fast update is enabled for the GIN index.
Valid value: ON and OFF
Default: ON
GIN_PENDING_LIST_LIMIT
Specifies the maximum capacity of the pending list of the GIN index when fast update is enabled for the GIN index.
Value range: 64-INT_MAX. The unit is KB.
Default value: The default value of gin_pending_list_limit depends on gin_pending_list_limit specified in GUC parameters. By default, the value is 4 MB.
INVISIBLE
Controls whether the optimizer generates index scan plans.
Value range:
ON indicates that no index scan plan is generated.
OFF indicates that an index scan plan is generated.
Default value: OFF
WHERE predicate
Creates a partial index. A partial index is an index that contains entries for only a portion of a table, usually a portion that is more useful for indexing than the rest of the table. For example, if you have a table that contains both billed and unbilled orders where the unbilled orders take up a small fraction of the total table and yet that is an often used section, you can improve performance by creating an index on just that portion. Another possible application is to use WHERE with UNIQUE to enforce uniqueness over a subset of a table.
Value range: predicate expression can refer only to columns of the underlying table, but it can use all columns, not just the ones being indexed. Presently, subquery and aggregate expressions are also forbidden in WHERE.
PARTITION index_partition_name
Specifies the name of the index partition.
Value range: a string. It must comply with the naming convention.
Examples¶
Create a sample table named tpcds.ship_mode_t1.
CREATE TABLE tpcds.ship_mode_t1 ( SM_SHIP_MODE_SK INTEGER NOT NULL, SM_SHIP_MODE_ID CHAR(16) NOT NULL, SM_TYPE CHAR(30) , SM_CODE CHAR(10) , SM_CARRIER CHAR(20) , SM_CONTRACT CHAR(20) ) DISTRIBUTE BY HASH(SM_SHIP_MODE_SK);
Create a unique index on the SM_SHIP_MODE_SK column in the tpcds.ship_mode_t1 table.
CREATE UNIQUE INDEX ds_ship_mode_t1_index1 ON tpcds.ship_mode_t1(SM_SHIP_MODE_SK);
Create a UNQIUE index on the SM_SHIP_MODE_SK column in the tpcds.ship_mode_t1 table and specify how to process null values.
CREATE UNIQUE INDEX ds_ship_mode_t1_index5 ON tpcds.ship_mode_t1(SM_SHIP_MODE_SK) NULLS NOT DISTINCT;
Add comment to the index when creating an index on the SM_SHIP_MODE_SK column of table tpcds.ship_mode_t1.
CREATE INDEX ds_ship_mode_t1_index_comment ON tpcds.ship_mode_t1(SM_SHIP_MODE_SK) COMMENT 'index';
Create a B-tree index on the SM_SHIP_MODE_SK column in the tpcds.ship_mode_t1 table.
CREATE INDEX ds_ship_mode_t1_index4 ON tpcds.ship_mode_t1 USING btree(SM_SHIP_MODE_SK);
Create an expression index on the SM_CODE column in the tpcds.ship_mode_t1 table.
CREATE INDEX ds_ship_mode_t1_index2 ON tpcds.ship_mode_t1(SUBSTR(SM_CODE,1 ,4));
Create a partial index on the SM_SHIP_MODE_SK column where SM_SHIP_MODE_SK is greater than 10 in the tpcds.ship_mode_t1 table.
CREATE UNIQUE INDEX ds_ship_mode_t1_index3 ON tpcds.ship_mode_t1(SM_SHIP_MODE_SK) WHERE SM_SHIP_MODE_SK>10;
Create a sample table named tpcds.customer_address_p1.
CREATE TABLE tpcds.customer_address_p1 ( CA_ADDRESS_SK INTEGER NOT NULL, CA_ADDRESS_ID CHAR(16) NOT NULL, CA_STREET_NUMBER CHAR(10) , CA_STREET_NAME VARCHAR(60) , CA_STREET_TYPE CHAR(15) , CA_SUITE_NUMBER CHAR(10) , CA_CITY VARCHAR(60) , CA_COUNTY VARCHAR(30) , CA_STATE CHAR(2) , CA_ZIP CHAR(10) , CA_COUNTRY VARCHAR(20) , CA_GMT_OFFSET DECIMAL(5,2) , CA_LOCATION_TYPE CHAR(20) ) DISTRIBUTE BY HASH(CA_ADDRESS_SK) PARTITION BY RANGE(CA_ADDRESS_SK) ( PARTITION p1 VALUES LESS THAN (3000), PARTITION p2 VALUES LESS THAN (5000) , PARTITION p3 VALUES LESS THAN (MAXVALUE) ) ENABLE ROW MOVEMENT;
Create the partitioned table index ds_customer_address_p1_index1 with the name of the index partition not specified.
CREATE INDEX ds_customer_address_p1_index1 ON tpcds.customer_address_p1(CA_ADDRESS_SK) LOCAL;
Create the partitioned table index ds_customer_address_p1_index2 with the name of the index partition specified.
CREATE INDEX ds_customer_address_p1_index2 ON tpcds.customer_address_p1(CA_ADDRESS_SK) LOCAL ( PARTITION CA_ADDRESS_SK_index1, PARTITION CA_ADDRESS_SK_index2, PARTITION CA_ADDRESS_SK_index3 ) ;
Create the partitioned table index ds_customer_address_p1_index_comment and add index comments.
CREATE INDEX ds_customer_address_p1_index_comment ON tpcds.customer_address_p1(CA_ADDRESS_SK) COMMENT 'index' LOCAL ( PARTITION CA_ADDRESS_SK_index1, PARTITION CA_ADDRESS_SK_index2, PARTITION CA_ADDRESS_SK_index3 ) ;