Plan Hint Optimization
In plan hints, you can specify a join order, join and scan operations, and the number of rows in a result to tune an execution plan, improving query performance.
Function
The hint syntax follow after a SELECT keyword and is written in the following format:
/*+ <plan hint>*/
You can specify multiple hints for a query plan and separate them by spaces. A hint specified for a query plan does not apply to its subquery plans. To specify a hint for a subquery, add the hint following the SELECT of this subquery.
For example:
select /*+ <plan_hint1> <plan_hint2> */ * from t1, (select /*+ <plan_hint3> */ from t2) where 1=1;
In the preceding command, <plan_hint1> and <plan_hint2> are the hints of a query, and <plan_hint3> is the hint of its subquery.
NOTICE:
If a hint is specified in the CREATE VIEW statement, the hint will be applied each time this view is used.
If the random plan function is enabled (plan_mode_seed is set to a value other than 0), the specified hint will not be used.
Scope
Currently, the following hints are supported:
- Join order hints (leading)
- Join operation hints, excluding the semi join, anti join, and unique plan hints
- Rows hints
- Scan operation hints, supporting only tablescan, indexscan, and indexonlyscan
- Sublink name hints
Precautions
Hints do not support Agg, Sort, Setop, or Subplan.
Example
The following is the original plan and is used for comparing with the optimized ones:
create table store
(
s_store_sk integer not null,
s_store_id char(16) not null,
s_rec_start_date date ,
s_rec_end_date date ,
s_closed_date_sk integer ,
s_store_name varchar(50) ,
s_number_employees integer ,
s_floor_space integer ,
s_hours char(20) ,
s_manager varchar(40) ,
s_market_id integer ,
s_geography_class varchar(100) ,
s_market_desc varchar(100) ,
s_market_manager varchar(40) ,
s_division_id integer ,
s_division_name varchar(50) ,
s_company_id integer ,
s_company_name varchar(50) ,
s_street_number varchar(10) ,
s_street_name varchar(60) ,
s_street_type char(15) ,
s_suite_number char(10) ,
s_city varchar(60) ,
s_county varchar(30) ,
s_state char(2) ,
s_zip char(10) ,
s_country varchar(20) ,
s_gmt_offset decimal(5,2) ,
s_tax_precentage decimal(5,2) ,
primary key (s_store_sk)
);
create table store_sales
(
ss_sold_date_sk integer ,
ss_sold_time_sk integer ,
ss_item_sk integer not null,
ss_customer_sk integer ,
ss_cdemo_sk integer ,
ss_hdemo_sk integer ,
ss_addr_sk integer ,
ss_store_sk integer ,
ss_promo_sk integer ,
ss_ticket_number integer not null,
ss_quantity integer ,
ss_wholesale_cost decimal(7,2) ,
ss_list_price decimal(7,2) ,
ss_sales_price decimal(7,2) ,
ss_ext_discount_amt decimal(7,2) ,
ss_ext_sales_price decimal(7,2) ,
ss_ext_wholesale_cost decimal(7,2) ,
ss_ext_list_price decimal(7,2) ,
ss_ext_tax decimal(7,2) ,
ss_coupon_amt decimal(7,2) ,
ss_net_paid decimal(7,2) ,
ss_net_paid_inc_tax decimal(7,2) ,
ss_net_profit decimal(7,2) ,
primary key (ss_item_sk, ss_ticket_number)
);
create table store_returns
(
sr_returned_date_sk integer ,
sr_return_time_sk integer ,
sr_item_sk integer not null,
sr_customer_sk integer ,
sr_cdemo_sk integer ,
sr_hdemo_sk integer ,
sr_addr_sk integer ,
sr_store_sk integer ,
sr_reason_sk integer ,
sr_ticket_number integer not null,
sr_return_quantity integer ,
sr_return_amt decimal(7,2) ,
sr_return_tax decimal(7,2) ,
sr_return_amt_inc_tax decimal(7,2) ,
sr_fee decimal(7,2) ,
sr_return_ship_cost decimal(7,2) ,
sr_refunded_cash decimal(7,2) ,
sr_reversed_charge decimal(7,2) ,
sr_store_credit decimal(7,2) ,
sr_net_loss decimal(7,2) ,
primary key (sr_item_sk, sr_ticket_number)
);
create table customer
(
c_customer_sk integer not null,
c_customer_id char(16) not null,
c_current_cdemo_sk integer ,
c_current_hdemo_sk integer ,
c_current_addr_sk integer ,
c_first_shipto_date_sk integer ,
c_first_sales_date_sk integer ,
c_salutation char(10) ,
c_first_name char(20) ,
c_last_name char(30) ,
c_preferred_cust_flag char(1) ,
c_birth_day integer ,
c_birth_month integer ,
c_birth_year integer ,
c_birth_country varchar(20) ,
c_login char(13) ,
c_email_address char(50) ,
c_last_review_date char(10) ,
primary key (c_customer_sk)
);
create table promotion
(
p_promo_sk integer not null,
p_promo_id char(16) not null,
p_start_date_sk integer ,
p_end_date_sk integer ,
p_item_sk integer ,
p_cost decimal(15,2) ,
p_response_target integer ,
p_promo_name char(50) ,
p_channel_dmail char(1) ,
p_channel_email char(1) ,
p_channel_catalog char(1) ,
p_channel_tv char(1) ,
p_channel_radio char(1) ,
p_channel_press char(1) ,
p_channel_event char(1) ,
p_channel_demo char(1) ,
p_channel_details varchar(100) ,
p_purpose char(15) ,
p_discount_active char(1) ,
primary key (p_promo_sk)
);
create table customer_address
(
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) ,
primary key (ca_address_sk)
);
create table item
(
i_item_sk integer not null,
i_item_id char(16) not null,
i_rec_start_date date ,
i_rec_end_date date ,
i_item_desc varchar(200) ,
i_current_price decimal(7,2) ,
i_wholesale_cost decimal(7,2) ,
i_brand_id integer ,
i_brand char(50) ,
i_class_id integer ,
i_class char(50) ,
i_category_id integer ,
i_category char(50) ,
i_manufact_id integer ,
i_manufact char(50) ,
i_size char(20) ,
i_formulation char(20) ,
i_color char(20) ,
i_units char(10) ,
i_container char(10) ,
i_manager_id integer ,
i_product_name char(50) ,
primary key (i_item_sk)
);
explain
select i_product_name product_name
,i_item_sk item_sk
,s_store_name store_name
,s_zip store_zip
,ad2.ca_street_number c_street_number
,ad2.ca_street_name c_street_name
,ad2.ca_city c_city
,ad2.ca_zip c_zip
,count(*) cnt
,sum(ss_wholesale_cost) s1
,sum(ss_list_price) s2
,sum(ss_coupon_amt) s3
FROM store_sales
,store_returns
,store
,customer
,promotion
,customer_address ad2
,item
WHERE ss_store_sk = s_store_sk AND
ss_customer_sk = c_customer_sk AND
ss_item_sk = i_item_sk and
ss_item_sk = sr_item_sk and
ss_ticket_number = sr_ticket_number and
c_current_addr_sk = ad2.ca_address_sk and
ss_promo_sk = p_promo_sk and
i_color in ('maroon','burnished','dim','steel','navajo','chocolate') and
i_current_price between 35 and 35 + 10 and
i_current_price between 35 + 1 and 35 + 15
group by i_product_name
,i_item_sk
,s_store_name
,s_zip
,ad2.ca_street_number
,ad2.ca_street_name
,ad2.ca_city
,ad2.ca_zip
;
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