CREATE TABLE (U-SQL): Creating a Table from a Query

  • Artikel

Summary

Often a script converts unstructured data in a file into a table, by first extracting the data using an EXTRACT expression and then inserting it into a table after some optional transformations. In order to simplify the process, U-SQL provides the ability to create a table from a U-SQL query expression. The CREATE TABLE AS statement will infer the schema from the query expression and will create a clustered table, thus the clustered index needs to be provided as part of the CREATE TABLE AS statement.

Syntax

Create_Managed_Table_As_Query_Statement :=                                                               
    'CREATE' 'TABLE' ['IF' 'NOT' 'EXISTS'] Identifier  
    Table_As_Query.

Table_As_Query :=  
    ( '(' Table_Index Horizontal_Partition_Specification ')'  
    | '(' Table_Index ')' Horizontal_Partition_Specification )  
    'AS' Query_Expression

Horizontal_Partition_Specification :=   
    'PARTITIONED' 'BY' Partition_Type  
    ['INTO' positive_integer_literal].

Remarks

  • Identifier
    Specifies the name of the schema. If the Identifier is a three-part identifier, the table will be created in the specified database and schema. If it is a two-part identifier, then the table will be created in the specified schema of the current database context. If the identifier is a simple identifier, then the table will be created in the current database and schema context.

    If a table or other object of the given name already exists in the specified database and schema context or the user has no permissions to create a table, an error is raised.

  • Table_Index
    Specifies the clustered index for the table. For more details on defining a table index, see CREATE TABLE (U-SQL): Creating a Table with Schema.

  • Horizontal_Partition_Specification
    Only horizontal partitioning is currently supported with the CREATE TABLE AS statement. For more detail on the partitioning schemes and options see CREATE TABLE (U-SQL): Creating a Table with Schema.

  • Query_Expression
    Provides the query expression that defines the schema of the data and provides the initial data values. Any U-SQL query expression can be used to create a table, including SELECT, EXTRACT, PRODUCE, invocation of a TVF etc..

Examples

  • The examples can be executed in Visual Studio with the Azure Data Lake Tools plug-in.
  • The examples below use the sample data, /Samples/Data/SearchLog.tsv, provided with your Data Lake Analytics account. See Prepare source data for additional information.

Creating a table from a query - an extract
The following example creates a table called searchLogTable from SearchLog.tsv.

DROP TABLE IF EXISTS dbo.searchLogTable;
CREATE TABLE dbo.searchLogTable (
       INDEX clx_UserId CLUSTERED(UserId ASC) 
       DISTRIBUTED BY HASH (UserId)
) AS EXTRACT UserId          int,
            Start           DateTime,
            Region          string,
            Query           string,
            Duration        int?,
            Urls            string,
            ClickedUrls     string
    FROM "/Samples/Data/SearchLog.tsv"
    USING Extractors.Tsv();

Creating a table from a query - a rowset variable
The following example creates a table called searchLogTable from SearchLog.tsv.

CREATE DATABASE IF NOT EXISTS TestReferenceDB; 
USE DATABASE TestReferenceDB;

// Extract data from file
@data = 
    EXTRACT UserId          int,
            Start           DateTime,
            Region          string,
            Query           string,
            Duration        int?,
            Urls            string,
            ClickedUrls     string
    FROM "/Samples/Data/SearchLog.tsv"
    USING Extractors.Tsv();

// Create table based on extraction and populate table
DROP TABLE IF EXISTS dbo.searchLogTable;
CREATE TABLE dbo.searchLogTable (
       INDEX clx_UserId CLUSTERED(UserId ASC) 
       DISTRIBUTED BY HASH (UserId)
) AS SELECT * FROM @data;

Creating a table from a query - another table
The following example creates a table called searchLogTableCopy from searchLogTable, created from prior example.

DROP TABLE IF EXISTS dbo.searchLogTableCopy;
CREATE TABLE dbo.searchLogTableCopy (
       INDEX clx_UserId CLUSTERED(UserId ASC) 
       DISTRIBUTED BY HASH (UserId)
) AS SELECT * FROM dbo.searchLogTable; // Can also use a View

Creating a table from a query - invocation of a TVF
The following example creates a table called searchLogFromFunction by invoking the fuction tvf_SearchLog which was created from Basic Syntax - tvf_SearchLog.

DROP TABLE IF EXISTS dbo.searchLogFromFunction;
CREATE TABLE dbo.searchLogFromFunction (
    INDEX clx_UserId CLUSTERED(UserId ASC)
    DISTRIBUTED BY HASH (UserId) 
    ) AS dbo.tvf_SearchLog();

See Also