EXECUTE DIRECT

Function

EXECUTE DIRECT executes an SQL statement on a specified node. Generally, the cluster automatically allocates an SQL statement to proper nodes. EXECUTE DIRECT is mainly used for database maintenance and testing.

Precautions

• Only a system administrator can run the EXECUTE DIRECT statement.
• To ensure data consistency across nodes, only the SELECT statement can be used. Transaction statements, DDL, and DML cannot be used.
• When the AVG aggregation calculation is performed on the specified DN using such statements, the result set is returned in array, for example, {4,2}. The result of sum is 4, and that of count is 2.
• CNs do not store user table data. Therefore, you do not need to specify a CN to perform SELECT queries on user tables. If the query statement contains a hidden remote call to start the transaction logic, the error message "Cannot send begin to other nodes as I'm not execute cn" is displayed.
• EXECUTE DIRECT cannot be nested. If the inner SQL statement to be executed is also EXECUTE DIRECT, run only the bottom-layer EXECUTE DIRECT statement.

Syntax

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EXECUTE DIRECT ON ( nodename [, ... ] ) query ;

Parameter Description

• nodename

  Specifies the node name.

  Value range: An existing node.

• query

  Specifies the query SQL statement that you want to execute.

Examples

Query records in table tpcds.customer_address on the dn_6001_6002 node:

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CREATE TABLE IF NOT EXISTS customer_address(a int,b int);
EXECUTE DIRECT ON(dn_6001_6002) 'select count(*) from customer_address';