–By Lori Brown @SQLSupahStah
After installing Service Pack 1 for SQL 2016, I ran across USE HINT and thought I would put out what I could find to document it. Here’s where you find info from Microsoft: https://msdn.microsoft.com/en-us/library/ms181714.aspx and here is a link for all of the bugs that are fixed in SP1: https://support.microsoft.com/en-us/kb/3182545
USE HINT ( ‘hint_name‘ ) Provides one or more additional hints to the query processor as specified by a hint name inside single quotation marks. Hint names are case-insensitive. USE HINT can be utilized without having to be a member of the sysadmin server role.
The following hint names are supported:
- ‘DISABLE_OPTIMIZED_NESTED_LOOP’ Instructs the query processor not to use a sort operation (batch sort) for optimized nested loop joins when generating a query plan. Equivalent to trace flag 2340.
- ‘FORCE_LEGACY_CARDINALITY_ESTIMATION’ Forces the query optimizer to use Cardinality Estimation model of SQL Server 2012 and earlier versions. Equivalent to trace flag 9481 or Database Scoped Configuration setting LEGACY_CARDINALITY_ESTIMATION=ON.
- ‘ENABLE_QUERY_OPTIMIZER_HOTFIXES’ Enables query optimizer hotfixes (changes released in SQL Server Cumulative Updates and Service Packs). Equivalent to trace flag 4199 or Database Scoped Configuration setting QUERY_OPTIMIZER_HOTFIXES=ON.
- ‘DISABLE_PARAMETER_SNIFFING’ Instructs query optimizer to use average data distribution while compiling a query with one or more parameters, making the query plan independent of the parameter value which was first used when the query was compiled. Equivalent to trace flag 4136 or Database Scoped Configuration setting PARAMETER_SNIFFING=OFF.
- ‘ASSUME_MIN_SELECTIVITY_FOR_FILTER_ESTIMATES’ Causes SQL Server to generate a plan using minimum selectivity when estimating AND predicates for filters to account for correlation. Equivalent to trace flag 4137 when used with cardinality estimation model of SQL Server 2012 and earlier versions, and has similar effect when trace flag 9471 is used with cardinality estimation model of SQL Server 2014 or higher.
- ‘DISABLE_OPTIMIZER_ROWGOAL’ Causes SQL Server to generate a plan that does not use row goal adjustments with queries that contain TOP, OPTION (FAST N), IN, or EXISTS keywords. Equivalent to trace flag 4138.
- ‘ENABLE_HIST_AMENDMENT_FOR_ASC_KEYS’ Enables automatically generated quick statistics (histogram amendment) for any leading index column for which cardinality estimation is needed. The histogram used to estimate cardinality will be adjusted at query compile time to account for actual maximum or minimum value of this column. Equivalent to trace flag 4139.
- ‘ASSUME_JOIN_PREDICATE_DEPENDS_ON_FILTERS’ Causes SQL Server to generate a query plan using the Simple Containment assumption instead of the default Base Containment assumption for joins, under the query optimizer Cardinality Estimation model of SQL Server 2014 or newer. Equivalent to trace flag 9476.
- ‘FORCE_DEFAULT_CARDINALITY_ESTIMATION’ Forces the Query Optimizer to use Cardinality Estimation model that corresponds to the current database compatibility level. Use this hint to override Database Scoped Configuration setting LEGACY_CARDINALITY_ESTIMATION=ON or trace flag 9481.
The list of all supported USE HINT names can be queried using the dynamic management view sys.dm_exec_valid_use_hints. More this view can be found here: https://msdn.microsoft.com/en-us/library/mt791356.aspx
Some USE HINT hints may conflict with trace flags enabled at the global or session level, or database scoped configuration settings. In this case, the query level hint (USE HINT) always takes precedence. If a USE HINT conflicts with another query hint or a trace flag enabled at the query level (such as by QUERYTRACEON), SQL Server will generate an error when trying to execute the query.
DECLARE @qty INT
SET @qty = 4
SELECT h.OrderDate, h.Freight, d.OrderQty, d.UnitPrice
FROM Sales.SalesOrderDetail d
JOIN Sales.SalesOrderHeader h ON (d.SalesOrderID = h.SalesOrderID)
WHERE d.OrderQty > @qty
OPTION (USE HINT(‘DISABLE_PARAMETER_SNIFFING’,‘DISABLE_OPTIMIZED_NESTED_LOOP’));
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