Postgres-XC tutorial PDF - PGCon

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JOINs
Example: Join on distribution key
EXPLAIN VERBOSE SELECT * FROM tab1, tab2 WHERE tab1.val = tab2.val;
QUERY PLAN
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Nested Loop – Perform JOIN on coordinator.
Output: tab1.val, tab1.val2, tab2.val, tab2.val2
Join Filter: (tab1.val = tab2.val)
Queries to datanodes to fetch the rows from tab1 and tab2
­> Data Node Scan on tab1
Output: tab1.val, tab1.val2
Remote query: SELECT val, val2 FROM ONLY tab1 WHERE true
­> Data Node Scan on tab2
Output: tab2.val, tab2.val2
Remote query: SELECT val, val2 FROM ONLY tab2 WHERE true
May 16th, 2012 Postgres­XC 55