A Common Table Expression (CTE) is a temporary result set derived from a simple query specified in a WITH clause, which immediately precedes a SELECT or INSERT keyword. The CTE is defined only within the execution scope of a single statement. One or more CTEs can be used in a Hive SELECT, INSERT, CREATE TABLE AS SELECT, or CREATE VIEW AS SELECT statement.
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Common Table Expressions are added in Hive 0.13.0 with HIVE-1180. |
Common Table Expression Syntax
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withClause: cteClause (, cteClause)*
cteClause: cte_name AS (select statment) |
Additional Grammar Rules
- The WITH clause is not supported within SubQuery Blocks
- CTEs are supported in Views, CTAS and INSERT statements.
- Recursive Queries are not supported.
Examples
CTE in Select Statements
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with q1 as ( select key from src where key = '5')
select *
from q1;
-- from style
with q1 as (select * from src where key= '5')
from q1
select *;
-- chaining CTEs
with q1 as ( select key from q2 where key = '5'),
q2 as ( select key from src where key = '5')
select * from (select key from q1) a;
-- union example
with q1 as (select * from src where key= '5'),
q2 as (select * from src s2 where key = '4')
select * from q1 union all select * from q2; |
CTE in Views, CTAS, and Insert Statements
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-- insert example
create table s1 like src;
with q1 as ( select key, value from src where key = '5')
from q1
insert overwrite table s1
select *;
-- ctas example
create table s2 as
with q1 as ( select key from src where key = '4')
select * from q1;
-- view example
create view v1 as
with q1 as ( select key from src where key = '5')
select * from q1;
select * from v1;
-- view example, name collision
create view v1 as
with q1 as ( select key from src where key = '5')
select * from q1;
with q1 as ( select key from src where key = '4')
select * from v1; |
In the second View example, a query's CTE is different from the CTE used when creating the view. The result will contain rows with key = '5' because in the view's query statement the CTE defined in the view definition takes effect.
Also see this JIRA:
- HIVE-1180 Support Common Table Expressions (CTEs) in Hive