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Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/optimizer/README | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/src/backend/optimizer/README b/src/backend/optimizer/README index f341d9f303c..21c2db5a85c 100644 --- a/src/backend/optimizer/README +++ b/src/backend/optimizer/README @@ -143,7 +143,6 @@ For example: {1 2},{2 3},{3 4} {1 2 3},{2 3 4} {1 2 3 4} - (other possibilities will be excluded for lack of join clauses) SELECT * FROM tab1, tab2, tab3, tab4 @@ -156,6 +155,11 @@ For example: {1 2 3},{1 3 4},{1 2 4} {1 2 3 4} +In each of these examples, other join-order possibilities will be excluded +for lack of join clauses. (In reality, use of EquivalenceClasses would +allow us to deduce additional join clauses that allow more join orders, +but here we ignore that to preserve the simplicity of the examples.) + We consider left-handed plans (the outer rel of an upper join is a joinrel, but the inner is always a single list item); right-handed plans (outer rel is always a single item); and bushy plans (both inner and outer can be |