JDBC Driver for HDFS

Build 21.0.7930

SELECT Statements

A SELECT statement can consist of the following basic clauses.

  • SELECT
  • INTO
  • FROM
  • JOIN
  • WHERE
  • GROUP BY
  • HAVING
  • UNION
  • ORDER BY
  • LIMIT

SELECT Syntax

The following syntax diagram outlines the syntax supported by the SQL engine of the driver:

SELECT {
  [ TOP <numeric_literal> | DISTINCT ]
  { 
    * 
    | { 
        <expression> [ [ AS ] <column_reference> ] 
        | { <table_name> | <correlation_name> } .* 
      } [ , ... ] 
  }
  [ INTO csv:// [ filename= ] <file_path> [ ;delimiter=tab ] ]
  { 
    FROM <table_reference> [ [ AS ] <identifier> ] 
  } [ , ... ]
  [ [  
      INNER | { { LEFT | RIGHT | FULL } [ OUTER ] } 
    ] JOIN <table_reference> [ ON <search_condition> ] [ [ AS ] <identifier> ] 
  ] [ ... ] 
  [ WHERE <search_condition> ]
  [ GROUP BY <column_reference> [ , ... ]
  [ HAVING <search_condition> ]
  [ UNION [ ALL ] <select_statement> ]
  [ 
    ORDER BY 
    <column_reference> [ ASC | DESC ] [ NULLS FIRST | NULLS LAST ]
  ]
  [ 
    LIMIT <expression>
    [ 
      { OFFSET | , }
      <expression> 
    ]
  ] 
}

<expression> ::=
  | <column_reference>
  | @ <parameter> 
  | ?
  | COUNT( * | { [ DISTINCT ] <expression> } )
  | { AVG | MAX | MIN | SUM | COUNT } ( <expression> ) 
  | NULLIF ( <expression> , <expression> ) 
  | COALESCE ( <expression> , ... ) 
  | CASE <expression>
      WHEN { <expression> | <search_condition> } THEN { <expression> | NULL } [ ... ]
    [ ELSE { <expression> | NULL } ]
    END 
  | <literal>
  | <sql_function> 

<search_condition> ::= 
  {
    <expression> { = | > | < | >= | <= | <> | != | LIKE | NOT LIKE | IN | NOT IN | IS NULL | IS NOT NULL | AND | OR | CONTAINS | BETWEEN } [ <expression> ]
  } [ { AND | OR } ... ] 

Examples

  1. Return all columns:
    SELECT * FROM Files
  2. Rename a column:
    SELECT [ChildrenNum] AS MY_ChildrenNum FROM Files
  3. Cast a column's data as a different data type:
    SELECT CAST(Length AS VARCHAR) AS Str_Length FROM Files
  4. Search data:
    SELECT * FROM Files WHERE FileId = '119116';
  5. Return the number of items matching the query criteria:
    SELECT COUNT(*) AS MyCount FROM Files 
  6. Return the number of unique items matching the query criteria:
    SELECT COUNT(DISTINCT ChildrenNum) FROM Files 
  7. Return the unique items matching the query criteria:
    SELECT DISTINCT ChildrenNum FROM Files 
  8. Summarize data:
    SELECT ChildrenNum, MAX(Length) FROM Files GROUP BY ChildrenNum
    See Aggregate Functions for details.
  9. Retrieve data from multiple tables.
    SELECT c.Owner, o.OwnerRead, o.OwnerWrite, o.OwnerExecute FROM Files c INNER JOIN Permissions o ON c.FullPath = o.FullPath
    See JOIN Queries for details.
  10. Sort a result set in ascending order:
    SELECT FileId, ChildrenNum FROM Files  ORDER BY ChildrenNum ASC
  11. Restrict a result set to the specified number of rows:
    SELECT FileId, ChildrenNum FROM Files LIMIT 10 
  12. Parameterize a query to pass in inputs at execution time. This enables you to create prepared statements and mitigate SQL injection attacks.
    SELECT * FROM Files WHERE FileId = @param
See Explicitly Caching Data for information on using the SELECT statement in offline mode.

Pseudo Columns

Some input-only fields are available in SELECT statements. These fields, called pseudo columns, do not appear as regular columns in the results, yet may be specified as part of the WHERE clause. You can use pseudo columns to access additional features from HDFS.

    SELECT * FROM Files WHERE Pseudo = '@Pseudo'
    

Copyright (c) 2021 CData Software, Inc. - All rights reserved.
Build 21.0.7930