sp_describe_first_result_set (Transact-SQL)

Returns the metadata for the first possible result set of the Transact-SQL batch. Returns an empty result set if the batch returns no results. Raises an error if the Database Engine cannot determine the metadata for the first query that will be executed by performing a static analysis. The dynamic management view sys.dm_exec_describe_first_result_set (Transact-SQL) returns the same information.

Transact-SQL Syntax Conventions

Składnia

sp_describe_first_result_set [ @tsql = ] N'Transact-SQL_batch' 
    [ , [ @params = ] N'parameters' ] 
    [ , [ @browse_information_mode = ] <tinyint> ] ]

Arguments

• [ @tsql = ] 'Transact-SQL_batch'
  One or more Transact-SQL statements. Transact-SQL_batch may be nvarchar(n) or nvarchar(max).

• [ @params = ] N'parameters'
  @params provides a declaration string for parameters for the Transact-SQL batch, which is similar to sp_executesql. Parameters may be nvarchar(n) or nvarchar(max).

  Is one string that contains the definitions of all parameters that have been embedded in the Transact-SQL_batch. The string must be either a Unicode constant or a Unicode variable. Each parameter definition consists of a parameter name and a data type. n is a placeholder that indicates additional parameter definitions. Every parameter specified in the statement must be defined in @params. If the Transact-SQL statement or batch in the statement does not contain parameters, @params is not required. NULL is the default value for this parameter.

• [ @browse_information_mode = ] tinyint
  Specifies if additional key columns and source table information are returned. If set to 1, each query is analyzed as if it includes a FOR BROWSE option on the query. Additional key columns and source table information are returned.

  • If set to 0, no information is returned.

  • If set to 1, each query is analyzed as if it includes a FOR BROWSE option on the query. This will return base table names as the source column information.

  • If set to 2, each query is analyzed as if it would be used in preparing or executing a cursor. This will return view names as source column information.

Return Code Values

sp_describe_first_result_set always returns a status of zero on success. If the procedure throws an error and the procedure is called as an RPC, return status is populated by the type of error described in the error_type column of sys.dm_exec_describe_first_result_set. If the procedure is called from Transact-SQL, the return value is always zero, even when there is an error.

Result Sets

This common metadata is returned as a result set with one row for each column in the results metadata. Each row describes the type and nullability of the column in the format described in the following section. If the first statement does not exist for every control path, a result set with zero rows is returned.

Column name	Data type	Description
is_hidden	bit NOT NULL	Indicates that the column is an extra column added for browsing information purposes and that it does not actually appear in the result set.
column_ordinal	int NOT NULL	Contains the ordinal position of the column in the result set. The first column’s position will be specified as 1.
name	sysname NULL	Contains the name of the column if a name can be determined. Otherwise, it will contain NULL.
is_nullable	bit NOT NULL	Contains the value 1 if the column allows NULLs, 0 if the column does not allow NULLs, and 1 if it cannot be determined if the column allows NULLs.
system_type_id	int NOT NULL	Contains the system_type_id of the data type of the column as specified in sys.types. For CLR types, even though the system_type_name column will return NULL, this column will return the value 240.
system_type_name	nvarchar(256) NULL	Contains the name and arguments (such as length, precision, scale), specified for the data type of the column. If the data type is a user-defined alias type, the underlying system type is specified here. If it is a CLR user-defined type, NULL is returned in this column.
max_length	smallint NOT NULL	Maximum length (in bytes) of the column. -1 = Column data type is varchar(max), nvarchar(max), varbinary(max), or xml. For text columns, the max_length value will be 16 or the value set by sp_tableoption 'text in row'.
precision	tinyint NOT NULL	Precision of the column if numeric-based. Otherwise returns 0.
scale	tinyint NOT NULL	Scale of column if numeric-based. Otherwise returns 0.
collation_name	sysname NULL	Name of the collation of the column if character-based. Otherwise returns NULL.
user_type_id	int NULL	For CLR and alias types, contains the user_type_id of the data type of the column as specified in sys.types. Otherwise is NULL.
user_type_database	sysname NULL	For CLR and alias types, contains the name of the database in which the type is defined. Otherwise is NULL.
user_type_schema	sysname NULL	For CLR and alias types, contains the name of the schema in which the type is defined. Otherwise is NULL.
user_type_name	sysname NULL	For CLR and alias types, contains the name of the type. Otherwise is NULL.
assembly_qualified_type_name	nvarchar(4000)	For CLR types, returns the name of the assembly and class defining the type. Otherwise is NULL.
xml_collection_id	int NULL	Contains the xml_collection_id of the data type of the column as specified in sys.columns. This column will return NULL if the type returned is not associated with an XML schema collection.
xml_collection_database	sysname NULL	Contains the database in which the XML schema collection associated with this type is defined. This column will return NULL if the type returned is not associated with an XML schema collection.
xml_collection_schema	sysname NULL	Contains the schema in which the XML schema collection associated with this type is defined. This column will return NULL if the type returned is not associated with an XML schema collection.
xml_collection_name	sysname NULL	Contains the name of the XML schema collection associated with this type. This column will return NULL if the type returned is not associated with an XML schema collection.
is_xml_document	bit NOT NULL	Returns 1 if the returned data type is XML and that type is guaranteed to be a complete XML document (including a root node), as opposed to an XML fragment). Otherwise returns 0.
is_case_sensitive	bit NOT NULL	Returns 1 if the column is a case-sensitive string type and 0 if it is not.
is_fixed_length_clr_type	bit NOT NULL	Returns 1 if the column is a fixed-length CLR type and 0 if it is not.
source_server	sysname	Name of the originating server returned by the column in this result (if it originates from a remote server). The name is given as it appears in sys.servers. Returns NULL if the column originates on the local server or if it cannot be determined which server it originates on. Is only populated if browsing information is requested.
source_database	sysname	Name of the originating database returned by the column in this result. Returns NULL if the database cannot be determined. Is only populated if browsing information is requested.
source_schema	sysname	Name of the originating schema returned by the column in this result. Returns NULL if the schema cannot be determined. Is only populated if browsing information is requested.
source_table	sysname	Name of the originating table returned by the column in this result. Returns NULL if the table cannot be determined. Is only populated if browsing information is requested.
source_column	sysname	Name of the originating column returned by the result column. Returns NULL if the column cannot be determined. Is only populated if browsing information is requested.
is_identity_column	bit NULL	Returns 1 if the column is an identity column and 0 if not. Returns NULL if it cannot be determined that the column is an identity column.
is_part_of_unique_key	bit NULL	Returns 1 if the column is part of a unique index (including unique and primary constraint) and 0 if not. Returns NULL if it cannot be determined that the column is part of a unique index. Only populated if browsing information is requested.
is_updateable	bit NULL	Returns 1 if the column is updateable and 0 if not. Returns NULL if it cannot be determined that the column is updateable.
is_computed_column	bit NULL	Returns 1 if the column is a computed column and 0 if not. Returns NULL if it cannot be determined that the column is a computed column.
is_sparse_column_set	bit NULL	Returns 1 if the column is a sparse column and 0 if not. Returns NULL if it cannot be determined that the column is part of a sparse column set.
ordinal_in_order_by_list	smallint NULL	Position of this column in ORDER BY list. Returns NULL if the column does not appear in the ORDER BY list or if the ORDER BY list cannot be uniquely determined.
order_by_list_length	smallint NULL	Length of the ORDER BY list. Returns NULL if there is no ORDER BY list or if the ORDER BY list cannot be uniquely determined. Note that this value will be the same for all rows returned by sp_describe_first_result_set.
order_by_is_descending	smallint NULL	If the ordinal_in_order_by_list is not NULL, the order_by_is_descending column reports the direction of the ORDER BY clause for this column. Otherwise it reports NULL.
tds_type_id	int NOT NULL	For internal use.
tds_length	int NOT NULL	For internal use.
tds_collation_id	int NULL	For internal use.
tds_collation_sort_id	tinyint NULL	For internal use.

Uwagi

sp_describe_first_result_set guarantees that if the procedure returns the first result-set metadata for (a hypothetical) batch A and if that batch (A) is subsequently executed then the batch will either (1) raises an optimization-time error, (2) raises a run-time error, (3) returns no result set, or (4) returns a first result set with the same metadata described by sp_describe_first_result_set.

The name, nullability, and data type can differ. If sp_describe_first_result_set returns an empty result set, the guarantee is that the batch execution will return no-result sets.

This guarantee presumes there are are no relevant schema changes on the server. Relevant schema changes on the server do not include creating a temporary tables or table variables in the batch A between the time that sp_describe_first_result_set is called and the time that the result set is returned during execution, including schema changes made by batch B.

sp_describe_first_result_set returns an error in any of the following cases.

• If the input @tsql is not a valid Transact-SQL batch. Validity is determined by parsing and analyzing the Transact-SQL batch. Any errors caused by the batch during query optimization or during execution are not considered when determining whether the Transact-SQL batch is valid.

• If @params is not NULL and contains a string that is not a syntactically valid declaration string for parameters, or if it contains a string that declares any parameter more than one time.

• If the input Transact-SQL batch declares a local variable of the same name as a parameter declared in @params.

• If the statement uses a temporary table.

• The query includes the creation of a permanent table that is then queried.

If all other checks succeed, all possible control flow paths inside the input batch are considered. This takes into account all control flow statements (GOTO, IF/ELSE, WHILE, and Transact-SQL TRY/CATCH blocks) as well as any procedures, dynamic Transact-SQL batches, or triggers invoked from the input batch by an EXEC statement, a DDL statement that causes DDL triggers to be fired, or a DML statement that causes triggers to be fired on a target table or on a table that is modified because of cascading action on a foreign key constraint. In the case of many possible control paths, at some point an algorithm stops.

For each control flow path, the first statement (if any) that returns a result set is determined by sp_describe_first_result_set.

When multiple possible first statements are found in a batch, their results can differ in number of columns, column name, nullability, and data type. How these differences are handled is described in more detail here:

• If the number of columns differs, an error is thrown and no result is returned.

• If the column name differs, the column name returned is set to NULL.

• It the nullability differs, the nullability returned will allow NULLs.

• If the data type differs, an error will be thrown and no result is returned except for the following cases:

  • varchar(a) to varchar(a') where a' > a.

  • varchar(a) to varchar(max)

  • nvarchar(a) to nvarchar(a') where a' > a.

  • nvarchar(a) to nvarchar(max)

  • varbinary(a) to varbinary(a') where a' > a.

  • varbinary(a) to varbinary(max)

sp_describe_first_result_set does not support indirect recursion.

Permissions

Requires permission to execute the @tsql argument.

Examples

Typical Examples

A. Simple Example

The following example describes the result set returned from a single query.

sp_describe_first_result_set @tsql = N'SELECT object_id, name, type_desc FROM sys.indexes'

The following example shows the result set returned from a single query that contains a parameter.

sp_describe_first_result_set @tsql = 
N'SELECT object_id, name, type_desc 
FROM sys.indexes 
WHERE object_id = @id1'
, @params = N'@id1 int'

B. Browse Mode Examples

The following three examples illustrate the key difference between the different browse information modes. Only the relevant columns have been included in the query results.

Example using 0 indicating no information is returned.

CREATE TABLE dbo.t (a int PRIMARY KEY, b1 int);
GO
CREATE VIEW dbo.v AS SELECT b1 AS b2 FROM dbo.t;
GO
EXEC sp_describe_first_result_set N'SELECT b2 AS b3 FROM dbo.v', null, 0;

Here is the result set.

is_hidden	column_ordinal	name	source_schema	source_table	source_column	is_part_of_unique_key
0	1	b3	NULL	NULL	NULL	NULL

Example using 1 indicating it returns information as if it includes a FOR BROWSE option on the query.

EXEC sp_describe_first_result_set N'SELECT b2 AS b3 FROM v', null, 1

Here is the result set.

is_hidden	column_ordinal	name	source_schema	source_table	source_column	is_part_of_unique_key
0	1	b3	dbo	t	B1	0
1	2	a	dbo	t	a	1

Example using 2 indicating analyzed as if you are preparing a cursor.

EXEC sp_describe_first_result_set N'SELECT b2 AS b3 FROM v', null, 2

Here is the result set.

is_hidden	column_ordinal	name	source_schema	source_table	source_column	is_part_of_unique_key
0	1	B3	dbo	v	B2	0
1	2	ROWSTAT	NULL	NULL	NULL	0

Examples of problems

The following examples use two tables for all examples. Execute the following statements to create the example tables.

CREATE TABLE dbo.t1 (a int NULL, b varchar(10) NULL, c nvarchar(10) NULL);
CREATE TABLE dbo.t2 (a smallint NOT NULL, d varchar(20) NOT NULL, e int NOT NULL);

Error because the number of columns differ

Number of columns in possible first result sets differ in this example.

sp_describe_first_result_set @tsql = 
N'
IF(1=1)
    SELECT a FROM t1;
ELSE
    SELECT a, b FROM t1;
SELECT * FROM t; -- Ignored, not a possible first result set.'

Error because the data types differ

Columns types differ in different possible first result sets.

sp_describe_first_result_set @tsql = 
N'
IF(1=1)
    SELECT a FROM t1;
ELSE
    SELECT a FROM t2;

Result: Error, mismatching types (int vs. smallint).

Column name cannot be determined

Columns in possible first result sets differ by length for same variable length type, nullability, and column names:

sp_describe_first_result_set @tsql = 
N'
IF(1=1)
    SELECT b FROM t1;
ELSE
    SELECT d FROM t2; '

Result: <Unknown Column Name> varchar(20) NULL

Column name forced to be identical through aliasing

Same as previous, but columns have the same name through column aliasing.

sp_describe_first_result_set @tsql = 
N'
IF(1=1)
    SELECT b FROM t1;
ELSE
    SELECT d AS b FROM t2;'

Result: b varchar(20) NULL

Error because column types cannot be matched

The columns types differ in different possible first result sets.

sp_describe_first_result_set @tsql = 
N'
IF(1=1)
    SELECT b FROM t1;
ELSE
    SELECT c FROM t1;'

Result: Error, mismatching types (varchar(10) vs. nvarchar(10)).

Result set can return an error

First result set is either error or result set.

sp_describe_first_result_set @tsql = 
N'
IF(1=1)
    RAISERROR(''Some Error'', 16, 1);

ELSE
    SELECT a FROM t1;
SELECT e FROM t2; -- Ignored, not a possible first result set.;'

Result: a int NULL

Some code paths return no results

First result set is either null or a result set.

sp_describe_first_result_set @tsql = 
N'
IF(1=1)
    RETURN;
SELECT a FROM t1;'

Result: a int NULL

Result from dynamic SQL

First result set is dynamic SQL that is discoverable because it is a literal string.

sp_describe_first_result_set @tsql = 
N'EXEC(N''SELECT a FROM t1'');'

Result: a INT NULL

Result failure from dynamic SQL

First result set is undefined because of dynamic SQL.

sp_describe_first_result_set @tsql = 
N'
DECLARE @SQL NVARCHAR(max);
SET @SQL = N''SELECT a FROM t1 WHERE 1 = 1 '';
IF(1=1)
    SET @SQL += N'' AND e > 10 '';
EXEC(@SQL); '

Result: Error. Result is not discoverable because of the dynamic SQL.

Result set specified by user

First result set is specified manually by user.

sp_describe_first_result_set @tsql = 
N'
DECLARE @SQL NVARCHAR(max);
SET @SQL = N''SELECT a FROM t1 WHERE 1 = 1 '';
IF(1=1)
    SET @SQL += N'' AND e > 10 '';
EXEC(@SQL)
    WITH RESULT SETS(
        (Column1 BIGINT NOT NULL)
    ); '

Result: Column1 bigint NOT NULL

Error caused by a ambiguous result set

This example assumes that another user named user1 has a table named t1 in the default schema s1 with columns (a int NOT NULL).

sp_describe_first_result_set @tsql = 
N'
    IF(@p > 0)
    EXECUTE AS USER = ''user1'';
    SELECT * FROM t1;'
, @params = N'@p int'

Result: Error. t1 can be either dbo.t1 or s1.t1, each with a different number of columns.

Result even with ambiguous result set

Use the same assumptions as the previous example.

sp_describe_first_result_set @tsql = 
N'
    IF(@p > 0)
    EXECUTE AS USER = ''user1'';
    SELECT a FROM t1;'

Result: a int NULL because both dbo.t1.a and s1.t1.a have type int and different nullability.

Zobacz także

Odwołanie

sp_describe_undeclared_parameters (Transact-SQL)

sys.dm_exec_describe_first_result_set (Transact-SQL)

sys.dm_exec_describe_first_result_set_for_object (Transact-SQL)