SET SHOWPLAN_ALL (Transact-SQL)

Artikkeli
12/03/2008

Causes Microsoft SQL Server not to execute Transact-SQL statements. Instead, SQL Server returns detailed information about how the statements are executed and provides estimates of the resource requirements for the statements.

Topic link icon Transact-SQL Syntax Conventions

Syntax

SET SHOWPLAN_ALL { ON | OFF }

Remarks

The setting of SET SHOWPLAN_ALL is set at execute or run time and not at parse time.

When SET SHOWPLAN_ALL is ON, SQL Server returns execution information for each statement without executing it, and Transact-SQL statements are not executed. After this option is set ON, information about all subsequent Transact-SQL statements are returned until the option is set OFF. For example, if a CREATE TABLE statement is executed while SET SHOWPLAN_ALL is ON, SQL Server returns an error message from a subsequent SELECT statement involving that same table, informing users that the specified table does not exist. Therefore, subsequent references to this table fail. When SET SHOWPLAN_ALL is OFF, SQL Server executes the statements without generating a report.

SET SHOWPLAN_ALL is intended to be used by applications written to handle its output. Use SET SHOWPLAN_TEXT to return readable output for Microsoft Win32 command prompt applications, such as the osql utility.

SET SHOWPLAN_TEXT and SET SHOWPLAN_ALL cannot be specified inside a stored procedure; they must be the only statements in a batch.

SET SHOWPLAN_ALL returns information as a set of rows that form a hierarchical tree representing the steps taken by the SQL Server query processor as it executes each statement. Each statement reflected in the output contains a single row with the text of the statement, followed by several rows with the details of the execution steps. The table shows the columns that the output contains.

Column name	Description
StmtText	For rows that are not of type PLAN_ROW, this column contains the text of the Transact-SQL statement. For rows of type PLAN_ROW, this column contains a description of the operation. This column contains the physical operator and may optionally also contain the logical operator. This column may also be followed by a description that is determined by the physical operator. For more information, see Logical and Physical Operators Reference.
StmtId	Number of the statement in the current batch.
NodeId	ID of the node in the current query.
Parent	Node ID of the parent step.
PhysicalOp	Physical implementation algorithm for the node. For rows of type PLAN_ROWS only.
LogicalOp	Relational algebraic operator this node represents. For rows of type PLAN_ROWS only.
Argument	Provides supplemental information about the operation being performed. The contents of this column depend on the physical operator.
DefinedValues	Contains a comma-separated list of values introduced by this operator. These values may be computed expressions which were present in the current query (for example, in the SELECT list or WHERE clause), or internal values introduced by the query processor in order to process this query. These defined values may then be referenced elsewhere within this query. For rows of type PLAN_ROWS only.
EstimateRows	Estimated number of rows of output produced by this operator. For rows of type PLAN_ROWS only.
EstimateIO	Estimated I/O cost for this operator. For rows of type PLAN_ROWS only.
EstimateCPU	Estimated CPU cost for this operator. For rows of type PLAN_ROWS only.
AvgRowSize	Estimated average row size (in bytes) of the row being passed through this operator.
TotalSubtreeCost	Estimated (cumulative) cost of this operation and all child operations.
OutputList	Contains a comma-separated list of columns being projected by the current operation.
Warnings	Contains a comma-separated list of warning messages relating to the current operation. Warning messages may include the string "NO STATS:()" with a list of columns. This warning message means that the query optimizer attempted to make a decision based on the statistics for this column, but none were available. Consequently, the query optimizer had to make a guess, which may have resulted in the selection of an inefficient query plan. For more information about creating or updating column statistics (which help the query optimizer choose a more efficient query plan), see UPDATE STATISTICS. This column may optionally include the string "MISSING JOIN PREDICATE", which means that a join (involving tables) is taking place without a join predicate. Accidentally dropping a join predicate may result in a query which takes much longer to run than expected, and returns a huge result set. If this warning is present, verify that the absence of a join predicate is intentional.
Type	Node type. For the parent node of each query, this is the Transact-SQL statement type (for example, SELECT, INSERT, EXECUTE, and so on). For subnodes representing execution plans, the type is PLAN_ROW.
Parallel	0 = Operator is not running in parallel. 1 = Operator is running in parallel.
EstimateExecutions	Estimated number of times this operator will be executed while running the current query.

Permissions

In order to use SET SHOWPLAN_ALL, you must have sufficient permissions to execute the statements on which SET SHOWPLAN_ALL is executed, and you must have SHOWPLAN permission for all databases containing referenced objects.

For SELECT, INSERT, UPDATE, DELETE, EXEC stored_procedure, and EXEC user_defined_function statements, to produce a Showplan the user must:

Have the appropriate permissions to execute the Transact-SQL statements.
Have SHOWPLAN permission on all databases containing objects referenced by the Transact-SQL statements, such as tables, views, and so on.

For all other statements, such as DDL, USE database_name, SET, DECLARE, dynamic SQL, and so on, only the appropriate permissions to execute the Transact-SQL statements are needed.

For more information, see Showplan Security and SHOWPLAN Permission and Transact-SQL Batches.

Examples

The two statements that follow use the SET SHOWPLAN_ALL settings to show the way SQL Server analyzes and optimizes the use of indexes in queries.

The first query uses the Equals comparison operator (=) in the WHERE clause on an indexed column. This results in the Clustered Index Seek value in the LogicalOp column and the name of the index in the Argument column.

The second query uses the LIKE operator in the WHERE clause. This forces SQL Server to use a clustered index scan and find the data that satisfies the WHERE clause condition. This results in the Clustered Index Scan value in the LogicalOp column with the name of the index in the Argument column, and the Filter value in the LogicalOp column with the WHERE clause condition in the Argument column.

The values in the EstimateRows and the TotalSubtreeCost columns are smaller for the first indexed query, indicating that it is processed much faster and uses fewer resources than the nonindexed query.

USE AdventureWorks;
GO
SET SHOWPLAN_ALL ON;
GO
-- First query.
SELECT EmployeeID 
FROM HumanResources.Employee
WHERE NationalIDNumber = '509647174';
GO
-- Second query.
SELECT EmployeeID, EmergencyContactID 
FROM HumanResources.Employee
WHERE EmergencyContactID LIKE '1%';
GO
SET SHOWPLAN_ALL OFF;
GO

Jaa

SET SHOWPLAN_ALL (Transact-SQL)

Syntax

Remarks

Permissions

Examples

See Also

Reference

Other Resources

Help and Information

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