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EXPLAIN PLAN

Function

EXPLAIN PLAN saves information about an execution plan into the PLAN_TABLE table. Different from the EXPLAIN statement, EXPLAIN PLAN only saves plan information and does not print information on the screen.

Syntax

EXPLAIN PLAN
[ SET STATEMENT_ID = string ]
FOR statement ;

Parameter Description

  • PLAN: saves plan information into PLAN_TABLE. If information is stored successfully, “EXPLAIN SUCCESS” is returned.
  • STATEMENT_ID: tags each query. The tag information will be stored in PLAN_TABLE.

    img NOTE: If the EXPLAIN PLAN statement does not contain SET STATEMENT_ID, STATEMENT_ID is empty by default. In addition, the value of STATEMENT_ID cannot exceed 30 bytes. Otherwise, an error will be reported.

Precautions

  • EXPLAIN PLAN cannot be executed on a database node.
  • Plan information cannot be collected for SQL statements that failed to be executed.
  • Data in PLAN_TABLE is in a session-level lifecycle. Sessions are isolated from users, and therefore users can only view the data of the current session and current user.

Example 1

You can perform the following steps to collect execution plans of SQL statements by running EXPLAIN PLAN:

  1. Run the EXPLAIN PLAN statement.

    img NOTE: After the EXPLAIN PLAN statement is executed, plan information is automatically stored in PLAN_TABLE. INSERT, UPDATE, and ANALYZE cannot be performed on PLAN_TABLE. For details about PLAN_TABLE, see PLAN_TABLE.

    explain plan set statement_id='TPCH-Q4' for
    select
    o_orderpriority,
    count(*) as order_count
    from
    orders
    where
    o_orderdate >= '1993-07-01'::date
    and o_orderdate < '1993-07-01'::date + interval '3 month'
    and exists (
    select
    *
    from
    lineitem
    where
    l_orderkey = o_orderkey
    and l_commitdate < l_receiptdate
    )
    group by
    o_orderpriority
    order by
    o_orderpriority;
  2. Query PLAN_TABLE.

    SELECT * FROM PLAN_TABLE;

    img

  3. Delete data from PLAN_TABLE.

    DELETE FROM PLAN_TABLE WHERE xxx;